/* SPDX-License-Identifier: GPL-2.0 */ /* * BPF extensible scheduler class: Documentation/scheduler/sched-ext.rst * * Copyright (c) 2022 Meta Platforms, Inc. and affiliates. * Copyright (c) 2022 Tejun Heo * Copyright (c) 2022 David Vernet */ #include #include #include #include #include #include #include #include "../pelt.h" #include "internal.h" #include "cid.h" #include "arena.h" #include "idle.h" #include "sub.h" #include "inlines.h" DEFINE_RAW_SPINLOCK(scx_sched_lock); /* * NOTE: sched_ext is in the process of growing multiple scheduler support and * scx_root usage is in a transitional state. Naked dereferences are safe if the * caller is one of the tasks attached to SCX and explicit RCU dereference is * necessary otherwise. Naked scx_root dereferences trigger sparse warnings but * are used as temporary markers to indicate that the dereferences need to be * updated to point to the associated scheduler instances rather than scx_root. */ struct scx_sched __rcu *scx_root; /* * All scheds, writers must hold both scx_enable_mutex and scx_sched_lock. * Readers can hold either or rcu_read_lock(). */ LIST_HEAD(scx_sched_all); #ifdef CONFIG_EXT_SUB_SCHED const struct rhashtable_params scx_sched_hash_params = { .key_len = sizeof_field(struct scx_sched, ops.sub_cgroup_id), .key_offset = offsetof(struct scx_sched, ops.sub_cgroup_id), .head_offset = offsetof(struct scx_sched, hash_node), .insecure_elasticity = true, /* inserted under scx_sched_lock */ }; struct rhashtable scx_sched_hash; #endif /* see SCX_OPS_TID_TO_TASK */ static const struct rhashtable_params scx_tid_hash_params = { .key_len = sizeof_field(struct sched_ext_entity, tid), .key_offset = offsetof(struct sched_ext_entity, tid), .head_offset = offsetof(struct sched_ext_entity, tid_hash_node), .insecure_elasticity = true, /* inserted/removed under scx_tasks_lock */ }; static struct rhashtable scx_tid_hash; /* * During exit, a task may schedule after losing its PIDs. When disabling the * BPF scheduler, we need to be able to iterate tasks in every state to * guarantee system safety. Maintain a dedicated task list which contains every * task between its fork and eventual free. */ static DEFINE_RAW_SPINLOCK(scx_tasks_lock); static LIST_HEAD(scx_tasks); /* ops enable/disable */ DEFINE_MUTEX(scx_enable_mutex); DEFINE_STATIC_KEY_FALSE(__scx_enabled); DEFINE_PERCPU_RWSEM(scx_fork_rwsem); static atomic_t scx_enable_state_var = ATOMIC_INIT(SCX_DISABLED); static DEFINE_RAW_SPINLOCK(scx_bypass_lock); static bool scx_init_task_enabled; static bool scx_switching_all; DEFINE_STATIC_KEY_FALSE(__scx_switched_all); static DEFINE_STATIC_KEY_FALSE(__scx_tid_to_task_enabled); /* * Gates cgroup ops delivery. Set at the end of the cgroup init phase of root * enable and cleared before root disable starts tearing down tasks, both under * scx_cgroup_lock(). Holding cgroup_lock() and seeing %true guarantees no race * against root tearing down tasks. */ bool scx_cgroup_enabled; /* * True once SCX_OPS_TID_TO_TASK has been negotiated with the root scheduler * and the tid->task table is live. Wraps the static key so callers don't * take the address, and hints "likely enabled" for the common case where * the feature is in use. */ static inline bool scx_tid_to_task_enabled(void) { return static_branch_likely(&__scx_tid_to_task_enabled); } static atomic_long_t scx_nr_rejected = ATOMIC_LONG_INIT(0); static atomic_long_t scx_hotplug_seq = ATOMIC_LONG_INIT(0); /* Global cursor for the per-CPU tid allocator. Starts at 1; tid 0 is reserved. */ static atomic64_t scx_tid_cursor = ATOMIC64_INIT(1); /* is @dsq synchronized by the containing rq lock instead of dsq->lock? */ static bool dsq_is_rq_owned(struct scx_dispatch_q *dsq) { switch (dsq->id) { case SCX_DSQ_LOCAL: case SCX_DSQ_REJECT: case SCX_DSQ_RESCUE: return true; default: return false; } } /* Cursor for unique scx_sched instance ids. id 0 is reserved. */ static atomic64_t scx_sched_id_cursor = ATOMIC64_INIT(0); #ifdef CONFIG_EXT_SUB_SCHED /* * The sub sched being enabled. Used by scx_disable_and_exit_task() to exit * tasks for the sub-sched being enabled. Use a global variable instead of a * per-task field as all enables are serialized. */ struct scx_sched *scx_enabling_sub_sched; #else #define scx_enabling_sub_sched (struct scx_sched *)NULL #endif /* CONFIG_EXT_SUB_SCHED */ /* * A monotonically increasing sequence number that is incremented every time a * scheduler is enabled. This can be used to check if any custom sched_ext * scheduler has ever been used in the system. */ static atomic_long_t scx_enable_seq = ATOMIC_LONG_INIT(0); /* * Watchdog interval. All scx_sched's share a single watchdog timer and the * interval is half of the shortest sch->watchdog_timeout. */ static unsigned long scx_watchdog_interval; /* * The last time the delayed work was run. This delayed work relies on * ksoftirqd being able to run to service timer interrupts, so it's possible * that this work itself could get wedged. To account for this, we check that * it's not stalled in the timer tick, and trigger an error if it is. */ static unsigned long scx_watchdog_timestamp = INITIAL_JIFFIES; static struct delayed_work scx_watchdog_work; /* * For %SCX_KICK_WAIT: Each CPU has a pointer to an array of kick_sync sequence * numbers. The arrays are allocated with kvzalloc() as size can exceed percpu * allocator limits on large machines. O(nr_cpu_ids^2) allocation, allocated * lazily when enabling and freed when disabling to avoid waste when sched_ext * isn't active. */ struct scx_kick_syncs { struct rcu_head rcu; unsigned long syncs[]; }; static DEFINE_PER_CPU(struct scx_kick_syncs __rcu *, scx_kick_syncs); /* * Per-CPU buffered allocator state for p->scx.tid. Each CPU pulls a chunk of * SCX_TID_CHUNK ids from scx_tid_cursor and hands them out locally without * further synchronization. See scx_alloc_tid(). */ struct scx_tid_alloc { u64 next; u64 end; }; static DEFINE_PER_CPU(struct scx_tid_alloc, scx_tid_alloc); /* * Direct dispatch marker. * * Non-NULL values are used for direct dispatch from enqueue path. A valid * pointer points to the task currently being enqueued. An ERR_PTR value is used * to indicate that direct dispatch has already happened. */ static DEFINE_PER_CPU(struct task_struct *, direct_dispatch_task); static const struct rhashtable_params dsq_hash_params = { .key_len = sizeof_field(struct scx_dispatch_q, id), .key_offset = offsetof(struct scx_dispatch_q, id), .head_offset = offsetof(struct scx_dispatch_q, hash_node), }; static LLIST_HEAD(dsqs_to_free); /* ops debug dump */ static DEFINE_RAW_SPINLOCK(scx_dump_lock); struct scx_dump_data { s32 cpu; bool first; s32 cursor; struct seq_buf *s; const char *prefix; struct scx_bstr_buf buf; }; static struct scx_dump_data scx_dump_data = { .cpu = -1, }; /* /sys/kernel/sched_ext interface */ static struct kset *scx_kset; /* * Parameters that can be adjusted through /sys/module/sched_ext/parameters. * There usually is no reason to modify these as normal scheduler operation * shouldn't be affected by them. The knobs are primarily for debugging. */ static unsigned int scx_slice_bypass_us = SCX_SLICE_BYPASS / NSEC_PER_USEC; static unsigned int scx_bypass_lb_intv_us = SCX_BYPASS_LB_DFL_INTV_US; static int set_slice_us(const char *val, const struct kernel_param *kp) { return param_set_uint_minmax(val, kp, 100, 100 * USEC_PER_MSEC); } static const struct kernel_param_ops slice_us_param_ops = { .set = set_slice_us, .get = param_get_uint, }; static int set_bypass_lb_intv_us(const char *val, const struct kernel_param *kp) { return param_set_uint_minmax(val, kp, 0, 10 * USEC_PER_SEC); } static const struct kernel_param_ops bypass_lb_intv_us_param_ops = { .set = set_bypass_lb_intv_us, .get = param_get_uint, }; #undef MODULE_PARAM_PREFIX #define MODULE_PARAM_PREFIX "sched_ext." module_param_cb(slice_bypass_us, &slice_us_param_ops, &scx_slice_bypass_us, 0600); MODULE_PARM_DESC(slice_bypass_us, "bypass slice in microseconds, applied on [un]load (100us to 100ms)"); module_param_cb(bypass_lb_intv_us, &bypass_lb_intv_us_param_ops, &scx_bypass_lb_intv_us, 0600); MODULE_PARM_DESC(bypass_lb_intv_us, "bypass load balance interval in microseconds (0 (disable) to 10s)"); #undef MODULE_PARAM_PREFIX #define CREATE_TRACE_POINTS #include static void run_deferred(struct rq *rq); static bool task_dead_and_done(struct task_struct *p); static void scx_disable(struct scx_sched *sch, enum scx_exit_kind kind); __printf(5, 6) bool __scx_exit(struct scx_sched *sch, enum scx_exit_kind kind, s64 exit_code, s32 exit_cpu, const char *fmt, ...) { va_list args; bool ret; va_start(args, fmt); ret = scx_vexit(sch, kind, exit_code, exit_cpu, fmt, args); va_end(args); return ret; } static long jiffies_delta_msecs(unsigned long at, unsigned long now) { if (time_after(at, now)) return jiffies_to_msecs(at - now); else return -(long)jiffies_to_msecs(now - at); } static bool u32_before(u32 a, u32 b) { return (s32)(a - b) < 0; } /** * scx_is_descendant - Test whether sched is a descendant * @sch: sched to test * @ancestor: ancestor sched to test against * * Test whether @sch is a descendant of @ancestor. */ bool scx_is_descendant(struct scx_sched *sch, struct scx_sched *ancestor) { if (sch->level < ancestor->level) return false; return sch->ancestors[ancestor->level] == ancestor; } static struct scx_dispatch_q *find_global_dsq(struct scx_sched *sch, s32 cpu) { return &sch->pnode[cpu_to_node(cpu)]->global_dsq; } static struct scx_dispatch_q *find_user_dsq(struct scx_sched *sch, u64 dsq_id) { return rhashtable_lookup(&sch->dsq_hash, &dsq_id, dsq_hash_params); } static const struct sched_class *scx_setscheduler_class(struct task_struct *p) { if (p->sched_class == &stop_sched_class) return &stop_sched_class; return __setscheduler_class(p->policy, p->prio); } static struct scx_dispatch_q *bypass_enq_target_dsq(struct scx_sched *sch, s32 cpu) { #ifdef CONFIG_EXT_SUB_SCHED /* * If @sch is a sub-sched which is bypassing, its tasks should go into * the bypass DSQs of the nearest ancestor which is not bypassing. The * not-bypassing ancestor is responsible for scheduling all tasks from * bypassing sub-trees. If all ancestors including root are bypassing, * all tasks should go to the root's bypass DSQs. * * Whenever a sched starts bypassing, all runnable tasks in its subtree * are re-enqueued after scx_bypassing() is turned on, guaranteeing that * all tasks are transferred to the right DSQs. */ while (scx_parent(sch) && scx_bypassing(sch, cpu)) sch = scx_parent(sch); #endif /* CONFIG_EXT_SUB_SCHED */ return scx_bypass_dsq(sch, cpu); } /** * rq_is_open - Is the rq available for immediate execution of an SCX task? * @rq: rq to test * @enq_flags: optional %SCX_ENQ_* of the task being enqueued * * Returns %true if @rq is currently open for executing an SCX task. After a * %false return, @rq is guaranteed to invoke SCX dispatch path at least once * before going to idle and not inserting a task into @rq's local DSQ after a * %false return doesn't cause @rq to stall. */ static bool rq_is_open(struct rq *rq, u64 enq_flags) { lockdep_assert_rq_held(rq); /* * A higher-priority class task is either running or in the process of * waking up on @rq. */ if (sched_class_above(rq->next_class, &ext_sched_class)) return false; /* * @rq is either in transition to or in idle and there is no * higher-priority class task waking up on it. */ if (sched_class_above(&ext_sched_class, rq->next_class)) return true; /* * @rq is either picking, in transition to, or running an SCX task. */ /* * If we're in the dispatch path holding rq lock, $curr may or may not * be ready depending on whether the on-going dispatch decides to extend * $curr's slice. We say yes here and resolve it at the end of dispatch. * See dispatch_one(). */ if (rq->scx.flags & SCX_RQ_IN_DISPATCH) return true; /* * %SCX_ENQ_PREEMPT clears $curr's slice if on SCX and kicks dispatch, * so allow it to avoid spuriously triggering reenq on a combined * PREEMPT|IMMED insertion. */ if (enq_flags & SCX_ENQ_PREEMPT) { struct task_struct *curr = rq->curr; /* * A protected slice refuses the preemption and the cpu stays * occupied. See rq_owned_post_enq(). */ return curr->sched_class != &ext_sched_class || likely(!(curr->scx.flags & SCX_TASK_PROTECTED)); } /* * @rq is either in transition to or running an SCX task and can't go * idle without another SCX dispatch cycle. */ return false; } /* * Track the rq currently locked. * * This allows kfuncs to safely operate on rq from any scx ops callback, * knowing which rq is already locked. */ DEFINE_PER_CPU(struct rq *, scx_locked_rq_state); /* * Under core scheduling, a pick that releases the rq lock invalidates the * core-wide selection it is part of. Count the releases so that the core-sched * pick can tell whether one happened across dispatch. */ static void scx_rq_lock_drop(struct rq *rq) { lockdep_assert_rq_held(rq); #ifdef CONFIG_SCHED_CORE if (sched_core_enabled(rq)) rq->scx.lock_drop_seq++; #endif } static void switch_rq_lock(struct rq *from, struct rq *to) { bool tracked = scx_locked_rq() == from; if (tracked) update_locked_rq(NULL); scx_rq_lock_drop(from); raw_spin_rq_unlock(from); raw_spin_rq_lock(to); if (tracked) update_locked_rq(to); } /* * Flipped on enable per sch->is_cid_type. Declared in internal.h so * subsystem inlines can read it. */ DEFINE_STATIC_KEY_FALSE(__scx_is_cid_type); /** * scx_call_op_set_cpumask - invoke ops.set_cpumask / ops_cid.set_cmask for @task * @sch: scx_sched being invoked * @rq: rq to update as the currently-locked rq, or NULL * @task: task whose affinity is changing * @cpumask: new cpumask * * For cid-form schedulers, translate @cpumask to a cmask via the per-cpu * scratch in cid.c and dispatch through the ops_cid union view. Caller * must hold @rq's rq lock so this_cpu_ptr is stable across the call. */ static inline void scx_call_op_set_cpumask(struct scx_sched *sch, struct rq *rq, struct task_struct *task, const struct cpumask *cpumask) { if (scx_is_cid_type()) { struct scx_cmask *kern_va = *this_cpu_ptr(sch->set_cmask_scratch); struct scx_cmask_ref ref; /* * Build the per-cpu arena cmask from kernel geometry via @ref, * never reading its BPF-writable header. set_cmask()'s __arena * argument takes the kernel address and the struct_ops * trampoline rebases it into BPF's arena pointer form. The rq * lock makes this cpu the sole kernel writer. */ scx_cmask_ref_init_kern(sch, kern_va, 0, num_possible_cpus(), &ref); scx_cmask_ref_from_cpumask(&ref, cpumask); SCX_CALL_CID_OP_TASK(sch, set_cmask, rq, task, kern_va); } else { SCX_CALL_OP_TASK(sch, set_cpumask, rq, task, cpumask); } } enum scx_dsq_iter_flags { /* iterate in the reverse dispatch order */ SCX_DSQ_ITER_REV = 1U << 16, __SCX_DSQ_ITER_HAS_SLICE = 1U << 30, __SCX_DSQ_ITER_HAS_VTIME = 1U << 31, __SCX_DSQ_ITER_USER_FLAGS = SCX_DSQ_ITER_REV, __SCX_DSQ_ITER_ALL_FLAGS = __SCX_DSQ_ITER_USER_FLAGS | __SCX_DSQ_ITER_HAS_SLICE | __SCX_DSQ_ITER_HAS_VTIME, }; /** * nldsq_next_task - Iterate to the next task in a non-local DSQ * @dsq: non-local dsq being iterated * @cur: current position, %NULL to start iteration * @rev: walk backwards * * Returns %NULL when iteration is finished. */ static struct task_struct *nldsq_next_task(struct scx_dispatch_q *dsq, struct task_struct *cur, bool rev) { struct list_head *list_node; struct scx_dsq_list_node *dsq_lnode; lockdep_assert_held(&dsq->lock); if (cur) list_node = &cur->scx.dsq_list.node; else list_node = &dsq->list; /* find the next task, need to skip BPF iteration cursors */ do { if (rev) list_node = list_node->prev; else list_node = list_node->next; if (list_node == &dsq->list) return NULL; dsq_lnode = container_of(list_node, struct scx_dsq_list_node, node); } while (dsq_lnode->flags & SCX_DSQ_LNODE_ITER_CURSOR); return container_of(dsq_lnode, struct task_struct, scx.dsq_list); } #define nldsq_for_each_task(p, dsq) \ for ((p) = nldsq_next_task((dsq), NULL, false); (p); \ (p) = nldsq_next_task((dsq), (p), false)) /** * nldsq_cursor_next_task - Iterate to the next task given a cursor in a non-local DSQ * @cursor: scx_dsq_list_node initialized with INIT_DSQ_LIST_CURSOR() * @dsq: non-local dsq being iterated * * Find the next task in a cursor based iteration. The caller must have * initialized @cursor using INIT_DSQ_LIST_CURSOR() and can release the DSQ lock * between the iteration steps. * * Only tasks which were queued before @cursor was initialized are visible. This * bounds the iteration and guarantees that vtime never jumps in the other * direction while iterating. */ static struct task_struct *nldsq_cursor_next_task(struct scx_dsq_list_node *cursor, struct scx_dispatch_q *dsq) { bool rev = cursor->flags & SCX_DSQ_ITER_REV; struct task_struct *p; lockdep_assert_held(&dsq->lock); BUG_ON(!(cursor->flags & SCX_DSQ_LNODE_ITER_CURSOR)); if (list_empty(&cursor->node)) p = NULL; else p = container_of(cursor, struct task_struct, scx.dsq_list); /* skip cursors and tasks that were queued after @cursor init */ do { p = nldsq_next_task(dsq, p, rev); } while (p && unlikely(u32_before(cursor->priv, p->scx.dsq_seq))); if (p) { if (rev) list_move_tail(&cursor->node, &p->scx.dsq_list.node); else list_move(&cursor->node, &p->scx.dsq_list.node); } else { list_del_init(&cursor->node); } return p; } /** * nldsq_cursor_lost_task - Test whether someone else took the task since iteration * @cursor: scx_dsq_list_node initialized with INIT_DSQ_LIST_CURSOR() * @rq: rq @p was on * @dsq: dsq @p was on * @p: target task * * @p is a task returned by nldsq_cursor_next_task(). The locks may have been * dropped and re-acquired inbetween. Verify that no one else took or is in the * process of taking @p from @dsq. * * On %false return, the caller can assume full ownership of @p. */ static bool nldsq_cursor_lost_task(struct scx_dsq_list_node *cursor, struct rq *rq, struct scx_dispatch_q *dsq, struct task_struct *p) { lockdep_assert_rq_held(rq); lockdep_assert_held(&dsq->lock); /* * @p could have already left $src_dsq, got re-enqueud, or be in the * process of being consumed by someone else. */ if (unlikely(p->scx.dsq != dsq || u32_before(cursor->priv, p->scx.dsq_seq) || p->scx.holding_cpu >= 0)) return true; /* if @p has stayed on @dsq, its rq couldn't have changed */ if (WARN_ON_ONCE(rq != task_rq(p))) return true; return false; } /* * BPF DSQ iterator. Tasks in a non-local DSQ can be iterated in [reverse] * dispatch order. BPF-visible iterator is opaque and larger to allow future * changes without breaking backward compatibility. Can be used with * bpf_for_each(). See bpf_iter_scx_dsq_*(). */ struct bpf_iter_scx_dsq_kern { struct scx_dsq_list_node cursor; struct scx_dispatch_q *dsq; u64 slice; u64 vtime; } __attribute__((aligned(8))); struct bpf_iter_scx_dsq { u64 __opaque[6]; } __attribute__((aligned(8))); u32 scx_get_task_state(const struct task_struct *p) { return p->scx.flags & SCX_TASK_STATE_MASK; } void scx_set_task_state(struct task_struct *p, u32 state) { u32 prev_state = scx_get_task_state(p); bool warn = false; switch (state) { case SCX_TASK_NONE: warn = prev_state == SCX_TASK_DEAD; break; case SCX_TASK_INIT_BEGIN: warn = prev_state != SCX_TASK_NONE; break; case SCX_TASK_INIT: warn = prev_state != SCX_TASK_INIT_BEGIN; p->scx.flags |= SCX_TASK_RESET_RUNNABLE_AT; break; case SCX_TASK_READY: warn = !(prev_state == SCX_TASK_INIT || prev_state == SCX_TASK_ENABLED); break; case SCX_TASK_ENABLED: warn = prev_state != SCX_TASK_READY; break; case SCX_TASK_DEAD: warn = !(prev_state == SCX_TASK_NONE || prev_state == SCX_TASK_INIT_BEGIN); break; default: WARN_ONCE(1, "sched_ext: Invalid task state %d -> %d for %s[%d]", prev_state, state, p->comm, p->pid); return; } WARN_ONCE(warn, "sched_ext: Invalid task state transition 0x%x -> 0x%x for %s[%d]", prev_state, state, p->comm, p->pid); p->scx.flags &= ~SCX_TASK_STATE_MASK; p->scx.flags |= state; } /** * scx_task_iter_start - Lock scx_tasks_lock and start a task iteration * @iter: iterator to init * @cgrp: Optional root of cgroup subhierarchy to iterate * * Initialize @iter. Once initialized, @iter must eventually be stopped with * scx_task_iter_stop(). * * If @cgrp is %NULL, scx_tasks is used for iteration and this function returns * with scx_tasks_lock held and @iter->cursor inserted into scx_tasks. * * If @cgrp is not %NULL, @cgrp and its descendants' tasks are walked using * @iter->css_iter. The caller must be holding cgroup_lock() to prevent cgroup * task migrations. * * The two modes of iterations are largely independent and it's likely that * scx_tasks can be removed in favor of always using cgroup iteration if * CONFIG_SCHED_CLASS_EXT depends on CONFIG_CGROUPS. * * scx_tasks_lock and the rq lock may be released using scx_task_iter_unlock() * between this and the first next() call or between any two next() calls. If * the locks are released between two next() calls, the caller is responsible * for ensuring that the task being iterated remains accessible either through * RCU read lock or obtaining a reference count. * * All tasks which existed when the iteration started are guaranteed to be * visited as long as they are not dead. */ void scx_task_iter_start(struct scx_task_iter *iter, struct cgroup *cgrp) { memset(iter, 0, sizeof(*iter)); #ifdef CONFIG_EXT_SUB_SCHED if (cgrp) { lockdep_assert_held(&cgroup_mutex); iter->cgrp = cgrp; iter->css_pos = css_next_descendant_pre(NULL, &iter->cgrp->self); css_task_iter_start(iter->css_pos, CSS_TASK_ITER_WITH_DEAD, &iter->css_iter); return; } #endif raw_spin_lock_irq(&scx_tasks_lock); iter->cursor = (struct sched_ext_entity){ .flags = SCX_TASK_CURSOR }; list_add(&iter->cursor.tasks_node, &scx_tasks); iter->list_locked = true; } static void __scx_task_iter_rq_unlock(struct scx_task_iter *iter) { if (iter->locked_task) { __balance_callbacks(iter->rq, &iter->rf); task_rq_unlock(iter->rq, iter->locked_task, &iter->rf); iter->locked_task = NULL; } } /** * scx_task_iter_unlock - Unlock rq and scx_tasks_lock held by a task iterator * @iter: iterator to unlock * * If @iter is in the middle of a locked iteration, it may be locking the rq of * the task currently being visited in addition to scx_tasks_lock. Unlock both. * This function can be safely called anytime during an iteration. The next * iterator operation will automatically restore the necessary locking. */ void scx_task_iter_unlock(struct scx_task_iter *iter) { __scx_task_iter_rq_unlock(iter); if (iter->list_locked) { iter->list_locked = false; raw_spin_unlock_irq(&scx_tasks_lock); } } static void __scx_task_iter_maybe_relock(struct scx_task_iter *iter) { if (!iter->list_locked) { raw_spin_lock_irq(&scx_tasks_lock); iter->list_locked = true; } } /** * scx_task_iter_relock - Re-acquire scx_tasks_lock and, optionally, @p's rq * @iter: iterator to relock * @p: task whose rq to lock, or %NULL for scx_tasks_lock only * * Counterpart to scx_task_iter_unlock(). Locking @p's rq is optional. Once * re-acquired, both locks are managed by the iterator from here on. */ static void scx_task_iter_relock(struct scx_task_iter *iter, struct task_struct *p) { __scx_task_iter_maybe_relock(iter); if (p) { iter->rq = task_rq_lock(p, &iter->rf); iter->locked_task = p; } } /** * scx_task_iter_stop - Stop a task iteration and unlock scx_tasks_lock * @iter: iterator to exit * * Exit a previously initialized @iter. Must be called with scx_tasks_lock held * which is released on return. If the iterator holds a task's rq lock, that rq * lock is also released. See scx_task_iter_start() for details. */ void scx_task_iter_stop(struct scx_task_iter *iter) { #ifdef CONFIG_EXT_SUB_SCHED if (iter->cgrp) { if (iter->css_pos) css_task_iter_end(&iter->css_iter); __scx_task_iter_rq_unlock(iter); return; } #endif __scx_task_iter_maybe_relock(iter); list_del_init(&iter->cursor.tasks_node); scx_task_iter_unlock(iter); } /** * scx_task_iter_next - Next task * @iter: iterator to walk * * Visit the next task. See scx_task_iter_start() for details. Locks are dropped * and re-acquired every %SCX_TASK_ITER_BATCH iterations to avoid causing stalls * by holding scx_tasks_lock for too long. */ static struct task_struct *scx_task_iter_next(struct scx_task_iter *iter) { struct list_head *cursor = &iter->cursor.tasks_node; struct sched_ext_entity *pos; if (!(++iter->cnt % SCX_TASK_ITER_BATCH)) { scx_task_iter_unlock(iter); cond_resched(); } #ifdef CONFIG_EXT_SUB_SCHED if (iter->cgrp) { while (iter->css_pos) { struct task_struct *p; p = css_task_iter_next(&iter->css_iter); if (p) return p; css_task_iter_end(&iter->css_iter); iter->css_pos = css_next_descendant_pre(iter->css_pos, &iter->cgrp->self); if (iter->css_pos) css_task_iter_start(iter->css_pos, CSS_TASK_ITER_WITH_DEAD, &iter->css_iter); } return NULL; } #endif __scx_task_iter_maybe_relock(iter); list_for_each_entry(pos, cursor, tasks_node) { if (&pos->tasks_node == &scx_tasks) return NULL; if (!(pos->flags & SCX_TASK_CURSOR)) { list_move(cursor, &pos->tasks_node); return container_of(pos, struct task_struct, scx); } } /* can't happen, should always terminate at scx_tasks above */ BUG(); } /** * scx_task_iter_next_locked - Next non-idle task with its rq locked * @iter: iterator to walk * * Visit the non-idle task with its rq lock held. Allows callers to specify * whether they would like to filter out dead tasks. See scx_task_iter_start() * for details. */ struct task_struct *scx_task_iter_next_locked(struct scx_task_iter *iter) { struct task_struct *p; __scx_task_iter_rq_unlock(iter); while ((p = scx_task_iter_next(iter))) { /* * scx_task_iter is used to prepare and move tasks into SCX * while loading the BPF scheduler and vice-versa while * unloading. The init_tasks ("swappers") should be excluded * from the iteration because: * * - It's unsafe to use __setschduler_prio() on an init_task to * determine the sched_class to use as it won't preserve its * idle_sched_class. * * - ops.init/exit_task() can easily be confused if called with * init_tasks as they, e.g., share PID 0. * * As init_tasks are never scheduled through SCX, they can be * skipped safely. Note that is_idle_task() which tests %PF_IDLE * doesn't work here: * * - %PF_IDLE may not be set for an init_task whose CPU hasn't * yet been onlined. * * - %PF_IDLE can be set on tasks that are not init_tasks. See * play_idle_precise() used by CONFIG_IDLE_INJECT. * * Test for idle_sched_class as only init_tasks are on it. */ if (p->sched_class == &idle_sched_class) continue; iter->rq = task_rq_lock(p, &iter->rf); iter->locked_task = p; /* * cgroup_task_dead() removes the dead tasks from cset->tasks * after sched_ext_dead() and cgroup iteration may see tasks * which already finished sched_ext_dead(). %SCX_TASK_DEAD is * set by sched_ext_dead() under @p's rq lock. Test it to * avoid visiting tasks which are already dead from SCX POV. */ if (scx_get_task_state(p) == SCX_TASK_DEAD) { __scx_task_iter_rq_unlock(iter); continue; } return p; } return NULL; } /** * scx_dump_event - Dump an event 'kind' in 'events' to 's' * @s: output seq_buf * @events: event stats * @kind: a kind of event to dump */ #define scx_dump_event(s, events, kind) do { \ scx_dump_line(&(s), "%40s: %16lld", #kind, (events)->kind); \ } while (0) static void scx_read_events(struct scx_sched *sch, struct scx_event_stats *events); static enum scx_enable_state scx_enable_state(void) { return atomic_read(&scx_enable_state_var); } static enum scx_enable_state scx_set_enable_state(enum scx_enable_state to) { return atomic_xchg(&scx_enable_state_var, to); } static bool scx_tryset_enable_state(enum scx_enable_state to, enum scx_enable_state from) { int from_v = from; return atomic_try_cmpxchg(&scx_enable_state_var, &from_v, to); } /** * wait_ops_state - Busy-wait the specified ops state to end * @p: target task * @opss: state to wait the end of * * Busy-wait for @p to transition out of @opss. This can only be used when the * state part of @opss is %SCX_QUEUEING or %SCX_DISPATCHING. This function also * has load_acquire semantics to ensure that the caller can see the updates made * in the enqueueing and dispatching paths. */ static void wait_ops_state(struct task_struct *p, unsigned long opss) { do { cpu_relax(); } while (atomic_long_read_acquire(&p->scx.ops_state) == opss); } static inline bool __cpu_valid(s32 cpu) { return likely(cpu >= 0 && cpu < nr_cpu_ids && cpu_possible(cpu)); } /** * scx_cpu_valid - Verify a cpu number, to be used on ops input args * @sch: scx_sched to abort on error * @cpu: cpu number which came from a BPF ops * @where: extra information reported on error * * @cpu is a cpu number which came from the BPF scheduler and can be any value. * Verify that it is in range and one of the possible cpus. If invalid, trigger * an ops error. */ bool scx_cpu_valid(struct scx_sched *sch, s32 cpu, const char *where) { if (__cpu_valid(cpu)) { return true; } else { scx_error(sch, "invalid CPU %d%s%s", cpu, where ? " " : "", where ?: ""); return false; } } static void deferred_bal_cb_workfn(struct rq *rq) { run_deferred(rq); } static void deferred_irq_workfn(struct irq_work *irq_work) { struct rq *rq = container_of(irq_work, struct rq, scx.deferred_irq_work); raw_spin_rq_lock(rq); run_deferred(rq); scx_rq_lock_drop(rq); raw_spin_rq_unlock(rq); } /** * schedule_deferred - Schedule execution of deferred actions on an rq * @rq: target rq * * Schedule execution of deferred actions on @rq. Deferred actions are executed * with @rq locked but unpinned, and thus can unlock @rq to e.g. migrate tasks * to other rqs. */ static void schedule_deferred(struct rq *rq) { /* * This is the fallback when schedule_deferred_locked() can't use * the cheaper balance callback or wakeup hook paths (the target * CPU is not in dispatch or wakeup). Currently, this is primarily * hit by reenqueue operations targeting a remote CPU. * * Queue on the target CPU. The deferred work can run from any CPU * correctly - the _locked() path already processes remote rqs from * the calling CPU - but targeting the owning CPU allows IPI delivery * without waiting for the calling CPU to re-enable IRQs and is * cheaper as the reenqueue runs locally. */ irq_work_queue_on(&rq->scx.deferred_irq_work, cpu_of(rq)); } /** * schedule_deferred_locked - Schedule execution of deferred actions on an rq * @rq: target rq * * Schedule execution of deferred actions on @rq. Equivalent to * schedule_deferred() but requires @rq to be locked and can be more efficient. */ static void schedule_deferred_locked(struct rq *rq) { lockdep_assert_rq_held(rq); /* * If in the middle of waking up a task, task_woken_scx() will be called * afterwards which will then run the deferred actions, no need to * schedule anything. */ if (rq->scx.flags & SCX_RQ_IN_WAKEUP) return; /* Don't do anything if there already is a deferred operation. */ if (rq->scx.flags & SCX_RQ_BAL_CB_PENDING) return; /* * If in dispatch, the balance callbacks will be called before rq lock * is released. Schedule one. * * * We can't directly insert the callback into the * rq's list: The call can drop its lock and make the pending balance * callback visible to unrelated code paths that call rq_pin_lock(). * * Just let dispatch_one() know that it must do it itself. */ if (rq->scx.flags & SCX_RQ_IN_DISPATCH) { rq->scx.flags |= SCX_RQ_BAL_CB_PENDING; return; } /* * No scheduler hooks available. Use the generic irq_work path. The * above WAKEUP and DISPATCH paths should cover most of the cases and * the time to IRQ re-enable shouldn't be long. */ schedule_deferred(rq); } void schedule_dsq_reenq(struct scx_sched *sch, struct scx_dispatch_q *dsq, u64 reenq_flags, struct rq *locked_rq) { struct rq *rq; /* * Allowing reenqueues doesn't make sense while bypassing. This also * blocks from new reenqueues to be scheduled on dead scheds. */ if (unlikely(READ_ONCE(sch->bypass_depth))) return; if (dsq->id == SCX_DSQ_LOCAL) { rq = container_of(dsq, struct rq, scx.local_dsq); /* * A sub-sched lacking baseline access on the target cid has no * business triggering IPIs. The lockless test is fine: slipping * through right after a revoke is harmless and a wrong denial * can't happen - if the caller has seen its ownership, so does * this test. */ if (unlikely(scx_missing_caps(sch, cpu_of(rq), SCX_CAP_BASE))) { __scx_add_event(sch, SCX_EV_SUB_REENQ_DENIED, 1); return; } struct scx_sched_pcpu *sch_pcpu = per_cpu_ptr(sch->pcpu, cpu_of(rq)); struct scx_deferred_reenq_local *drl = &sch_pcpu->deferred_reenq_local; /* * Pairs with smp_mb() in process_deferred_reenq_locals() and * guarantees that there is a reenq_local() afterwards. */ smp_mb(); if (list_empty(&drl->node) || (READ_ONCE(drl->flags) & reenq_flags) != reenq_flags) { guard(raw_spinlock_irqsave)(&rq->scx.deferred_reenq_lock); if (list_empty(&drl->node)) list_move_tail(&drl->node, &rq->scx.deferred_reenq_locals); WRITE_ONCE(drl->flags, drl->flags | reenq_flags); } } else if (!(dsq->id & SCX_DSQ_FLAG_BUILTIN)) { rq = this_rq(); struct scx_dsq_pcpu *dsq_pcpu = per_cpu_ptr(dsq->pcpu, cpu_of(rq)); struct scx_deferred_reenq_user *dru = &dsq_pcpu->deferred_reenq_user; /* * Pairs with smp_mb() in process_deferred_reenq_users() and * guarantees that there is a reenq_user() afterwards. */ smp_mb(); if (list_empty(&dru->node) || (READ_ONCE(dru->flags) & reenq_flags) != reenq_flags) { guard(raw_spinlock_irqsave)(&rq->scx.deferred_reenq_lock); if (list_empty(&dru->node)) list_move_tail(&dru->node, &rq->scx.deferred_reenq_users); WRITE_ONCE(dru->flags, dru->flags | reenq_flags); } } else { scx_error(sch, "DSQ 0x%llx not allowed for reenq", dsq->id); return; } if (rq == locked_rq) schedule_deferred_locked(rq); else schedule_deferred(rq); } /* * p->scx.slice_oob packs an out-of-band slice request into one atomic64. A zero * word means no request. Otherwise the fields are: * * 63 SCX_SLICE_OOB_PENDING, set on every request * 62-43 lower bits of issuing scheduler's id * 42-0 requested slice duration in nsecs * * A duration of SCX_SLICE_OOB_DUR_MASK means SCX_SLICE_INF. A finite dur * saturates at SCX_SLICE_OOB_DUR_MASK - 1. The id is used to detect and ignore * a request that outlived a task ownership change. * * Only the low 20 bits of sch->id are packed, which is enough to make * collisions practically impossible. A theoretical collision just lets a stale * request through once. */ enum scx_slice_oob_consts { SCX_SLICE_OOB_DUR_BITS = 43, SCX_SLICE_OOB_ID_BITS = 64 - SCX_SLICE_OOB_DUR_BITS - 1, SCX_SLICE_OOB_DUR_MASK = (1LLU << SCX_SLICE_OOB_DUR_BITS) - 1, SCX_SLICE_OOB_ID_SHIFT = SCX_SLICE_OOB_DUR_BITS, SCX_SLICE_OOB_ID_MASK = (1LLU << SCX_SLICE_OOB_ID_BITS) - 1, SCX_SLICE_OOB_PENDING = 1LLU << 63, }; /* * Slice and dsq_vtime write rules * * While @p is running, sleeping or queued on an rq-owned DSQ, both fields are * protected by the rq lock. While running, the rq lock is required because * update_curr_scx() RMWs the slice and the cap check for slice extension is * only reliable under the rq lock. * * While @p is queued on a user DSQ or on the BPF side, the kernel neither * consumes nor decides on the fields. Synchronizing the writers is the BPF * scheduler's responsibility. An rq-locked scx_bpf_task_set_slice() write and a * concurrent DSQ insertion commit can race each other and whichever lands last * wins. * * A DSQ insert kfunc doesn't update the fields directly. The verdict carries * the values and apply_slice_vtime() commits them at the insertion. * * scx_bpf_task_set_slice() may be called from any context and writes directly * only if @p's rq lock is already held, otherwise it bounces through * p->scx.slice_oob, applied under @p's rq lock at the next slice consideration. * * While %SCX_TASK_PROTECTED is set, every scheduler-reachable slice update is * refused. See set_task_slice_keep_oob(). * * dsq_vtime orders the next PRIQ insertion and has no running-side consumer, so * scx_bpf_task_set_dsq_vtime() writes it directly. Fork-time init and direct * BPF stores from non-cid-form schedulers are outside these rules. */ /* clear a pending slice request */ static void clear_task_slice_oob(struct task_struct *p) { if (unlikely(atomic64_read(&p->scx.slice_oob))) atomic64_set(&p->scx.slice_oob, 0); } /** * dsq_insert_head - FIFO head insertion honoring %SCX_TASK_PROTECTED * @dsq: DSQ to insert into * @p: task being inserted * * A HEAD insert should land behind any leading protected tasks. Return %true * indicates whether @p became the first entry. */ static bool dsq_insert_head(struct scx_dispatch_q *dsq, struct task_struct *p) { struct list_head *pos = &dsq->list; struct scx_dsq_list_node *node; /* * Only rq-owned DSQs can hold protected tasks and the associated rq * lock keeps their flags stable. */ if (!dsq_is_rq_owned(dsq)) { list_add(&p->scx.dsq_list.node, &dsq->list); return true; } list_for_each_entry(node, &dsq->list, node) { struct task_struct *q; if (WARN_ON_ONCE(node->flags & SCX_DSQ_LNODE_ITER_CURSOR)) continue; q = container_of(node, struct task_struct, scx.dsq_list); if (!(q->scx.flags & SCX_TASK_PROTECTED)) break; pos = &node->node; } list_add(&p->scx.dsq_list.node, pos); return pos == &dsq->list; } /** * set_task_slice_keep_oob - Set @p's slice, leaving any pending oob request * @p: task of interest * @slice: slice to set * * While %SCX_TASK_PROTECTED is set, BPF schedulers may not modify the slice. * Refuse and return %false. */ static bool set_task_slice_keep_oob(struct task_struct *p, u64 slice) { lockdep_assert_rq_held(task_rq(p)); if (unlikely(p->scx.flags & SCX_TASK_PROTECTED)) return false; p->scx.slice = slice; return true; } /* set @p's slice, superseding any pending out-of-band request */ bool scx_set_task_slice(struct task_struct *p, u64 slice) { if (!set_task_slice_keep_oob(p, slice)) return false; clear_task_slice_oob(p); return true; } /** * scx_task_slice_ended - @p's slice is consumed or given up * @rq: rq @p is on * @p: task of interest * * End what rides on the slice - the protection, and the rescue if @p is being * rescued. * * A dequeue normally ends the slice too. The exception is a save/restore pair * on the running task. Attribute changes like renice cycle the task through * dequeue and enqueue while it keeps executing, so the slice continues. A * queued task instead loses its DSQ position on any dequeue and the slice ends * with it. */ void scx_task_slice_ended(struct rq *rq, struct task_struct *p) { lockdep_assert_rq_held(rq); p->scx.flags &= ~SCX_TASK_PROTECTED; if (unlikely(p == scx_rescuee(rq))) scx_rescue_end(rq); } /* request @p's slice to be set to @slice, see the write rules above */ static void set_task_slice_oob(struct scx_sched *sch, struct task_struct *p, u64 slice) { u64 dur; if (slice == SCX_SLICE_INF) { dur = SCX_SLICE_OOB_DUR_MASK; } else if (unlikely(slice >= SCX_SLICE_OOB_DUR_MASK)) { dur = SCX_SLICE_OOB_DUR_MASK - 1; scx_add_event(sch, SCX_EV_SLICE_CLAMPED, 1); } else { dur = slice; } atomic64_set(&p->scx.slice_oob, SCX_SLICE_OOB_PENDING | ((sch->id & SCX_SLICE_OOB_ID_MASK) << SCX_SLICE_OOB_ID_SHIFT) | dur); } /* * Apply a pending out-of-band slice request under @rq's lock. A request whose * packed id no longer matches @p's current owner is dropped. An extension needs * baseline cpu access on @p's cid, shortening is always allowed, and a * protected slice refuses both. %SCX_EV_SLICE_DENIED counts the denials. See * the write rules above. */ static void apply_task_slice_oob(struct rq *rq, struct task_struct *p) { u64 oob, dur, slice; lockdep_assert_rq_held(rq); if (likely(!atomic64_read(&p->scx.slice_oob))) return; oob = atomic64_xchg(&p->scx.slice_oob, 0); if (unlikely(!oob)) return; /* the issuing scheduler no longer owns @p, drop the request */ if (unlikely(((oob >> SCX_SLICE_OOB_ID_SHIFT) & SCX_SLICE_OOB_ID_MASK) != (scx_task_sched(p)->id & SCX_SLICE_OOB_ID_MASK))) return; dur = oob & SCX_SLICE_OOB_DUR_MASK; slice = dur == SCX_SLICE_OOB_DUR_MASK ? SCX_SLICE_INF : dur; if (slice > p->scx.slice && unlikely(scx_missing_caps(scx_task_sched(p), cpu_of(rq), SCX_CAP_BASE))) { __scx_add_event(scx_task_sched(p), SCX_EV_SLICE_DENIED, 1); return; } if (unlikely(!set_task_slice_keep_oob(p, slice))) __scx_add_event(scx_task_sched(p), SCX_EV_SLICE_DENIED, 1); } /* * A dsq insert kfunc doesn't write slice or dsq_vtime. The verdict carries them * and they are committed here, at the insertion. A zero @slice keeps the * current value, floored at 1 so the task isn't treated as expired. */ static void apply_slice_vtime(struct task_struct *p, u64 slice, u64 vtime, u64 enq_flags) { if (slice) { p->scx.slice = slice; /* * An explicit slice supersedes a pending oob request. A carried * default refill is not an explicit request and must keep it. */ if (!(enq_flags & SCX_ENQ_SLICE_DFL)) clear_task_slice_oob(p); } else if (!p->scx.slice) { p->scx.slice = 1; } if (enq_flags & SCX_ENQ_DSQ_PRIQ) p->scx.dsq_vtime = vtime; } static void update_curr_scx(struct rq *rq) { struct task_struct *curr = rq->curr; s64 delta_exec; /* apply even on 0 delta_exec, callers may still act on the slice */ apply_task_slice_oob(rq, curr); delta_exec = update_curr_common(rq); if (unlikely(delta_exec <= 0)) return; if (curr->scx.slice != SCX_SLICE_INF) curr->scx.slice -= min_t(u64, curr->scx.slice, delta_exec); if (unlikely(curr == scx_rescuee(rq))) scx_rescue_charge(rq, delta_exec); dl_server_update(&rq->ext_server, delta_exec); } static bool scx_dsq_priq_less(struct rb_node *node_a, const struct rb_node *node_b) { const struct task_struct *a = container_of(node_a, struct task_struct, scx.dsq_priq); const struct task_struct *b = container_of(node_b, struct task_struct, scx.dsq_priq); return time_before64(a->scx.dsq_vtime, b->scx.dsq_vtime); } static void dsq_inc_nr(struct scx_dispatch_q *dsq, struct task_struct *p, u64 enq_flags) { /* scx_bpf_dsq_nr_queued() reads ->nr without locking, use WRITE_ONCE() */ WRITE_ONCE(dsq->nr, dsq->nr + 1); /* * Once @p reaches a local DSQ, it can only leave it by being dispatched * to the CPU or dequeued. In both cases, the only way @p can go back to * the BPF sched is through enqueueing. If being inserted into a local * DSQ with IMMED, persist the state until the next enqueueing event in * scx_do_enqueue_task() so that we can maintain IMMED protection * through e.g. SAVE/RESTORE cycles and slice extensions. */ if (enq_flags & SCX_ENQ_IMMED) { if (unlikely(dsq->id != SCX_DSQ_LOCAL)) { WARN_ON_ONCE(!(enq_flags & SCX_ENQ_GDSQ_FALLBACK)); return; } p->scx.flags |= SCX_TASK_IMMED; } if (p->scx.flags & SCX_TASK_IMMED) { struct rq *rq = container_of(dsq, struct rq, scx.local_dsq); if (WARN_ON_ONCE(dsq->id != SCX_DSQ_LOCAL)) return; rq->scx.nr_immed++; /* * If @rq already had other tasks or the current task is not * done yet, @p can't go on the CPU immediately. Re-enqueue. */ if (unlikely(dsq->nr > 1 || !rq_is_open(rq, enq_flags))) scx_schedule_reenq_local(rq, 0); } } static void dsq_dec_nr(struct scx_dispatch_q *dsq, struct task_struct *p) { /* see dsq_inc_nr() */ WRITE_ONCE(dsq->nr, dsq->nr - 1); if (p->scx.flags & SCX_TASK_IMMED) { struct rq *rq = container_of(dsq, struct rq, scx.local_dsq); if (WARN_ON_ONCE(dsq->id != SCX_DSQ_LOCAL) || WARN_ON_ONCE(rq->scx.nr_immed <= 0)) return; rq->scx.nr_immed--; } } static void refill_task_slice_dfl(struct scx_sched *sch, struct task_struct *p) { /* * A default refill is not an explicit request, so it must not drop a * pending out-of-band one, which is applied when @p next runs. */ set_task_slice_keep_oob(p, READ_ONCE(sch->slice_dfl)); __scx_add_event(sch, SCX_EV_REFILL_SLICE_DFL, 1); } /* * Return true if @p is moving due to an internal SCX migration, false * otherwise. */ static inline bool task_scx_migrating(struct task_struct *p) { /* * We only need to check sticky_cpu: it is set to the destination * CPU in move_remote_task_to_local_dsq() before deactivate_task() * and cleared when the task is enqueued on the destination, so it * is only non-negative during an internal SCX migration. */ return p->scx.sticky_cpu >= 0; } /* * Call ops.dequeue() if the task is in BPF custody and not migrating. * Clears %SCX_TASK_IN_CUSTODY when the callback is invoked. */ static void call_task_dequeue(struct scx_sched *sch, struct rq *rq, struct task_struct *p, u64 deq_flags) { if (!(p->scx.flags & SCX_TASK_IN_CUSTODY) || task_scx_migrating(p)) return; if (SCX_HAS_OP(sch, dequeue)) SCX_CALL_OP_TASK(sch, dequeue, rq, p, deq_flags); p->scx.flags &= ~SCX_TASK_IN_CUSTODY; } static void rq_owned_post_enq(struct scx_sched *sch, struct rq *rq, struct scx_dispatch_q *dsq, struct task_struct *p, u64 enq_flags) { call_task_dequeue(sch, rq, p, 0); /* * Only local inserts get the wakeup treatment below. Rejects kick the * deferred reenq and rescue parks are paced by the rescue timer. */ if (unlikely(dsq->id != SCX_DSQ_LOCAL)) { if (dsq->id == SCX_DSQ_REJECT) schedule_deferred_locked(rq); return; } /* * Note that @rq's lock may be dropped between this enqueue and @p * actually getting on CPU. This gives higher-class tasks (e.g. RT) * an opportunity to wake up on @rq and prevent @p from running. * Here are some concrete examples: * * Example 1: * * We dispatch two tasks from a single ops.dispatch(): * - First, a local task to this CPU's local DSQ; * - Second, a local/remote task to a remote CPU's local DSQ. * We must drop the local rq lock in order to finish the second * dispatch. In that time, an RT task can wake up on the local rq. * * Example 2: * * We dispatch a local/remote task to a remote CPU's local DSQ. * We must drop the remote rq lock before the dispatched task can run, * which gives an RT task an opportunity to wake up on the remote rq. * * Both examples work the same if we replace dispatching with moving * the tasks from a user-created DSQ. * * We must detect these wakeups so that we can re-enqueue IMMED tasks * from @rq's local DSQ. scx_wakeup_preempt() serves exactly this * purpose, but for it to be invoked, we must ensure that we bump * @rq->next_class to &ext_sched_class if it's currently idle. * * wakeup_preempt() does the bumping, and since we only invoke it if * @rq->next_class is below &ext_sched_class, it will also * resched_curr(rq). */ if (sched_class_above(p->sched_class, rq->next_class)) wakeup_preempt(rq, p, 0); /* * If @rq is in dispatch, the CPU is already vacant and looking for the * next task to run. No need to preempt or trigger resched after moving * @p into its local DSQ. * Note that the wakeup_preempt() above may have already triggered * a resched if @rq->next_class was idle. It's harmless, since * need_resched is cleared immediately after task pick. */ if (rq->scx.flags & SCX_RQ_IN_DISPATCH) return; if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->curr && rq->curr->sched_class == &ext_sched_class) { if (likely(scx_set_task_slice(rq->curr, 0))) resched_curr(rq); else __scx_add_event(sch, SCX_EV_SLICE_DENIED, 1); } } static void scx_dispatch_enqueue(struct scx_sched *sch, struct rq *rq, struct scx_dispatch_q *dsq, struct task_struct *p, u64 slice, u64 vtime, u64 enq_flags) { bool is_rq_owned = false; if (dsq->id == SCX_DSQ_LOCAL) { dsq = scx_resolve_local_dsq(sch, rq, p, &enq_flags); is_rq_owned = true; } WARN_ON_ONCE(p->scx.dsq || !list_empty(&p->scx.dsq_list.node)); WARN_ON_ONCE((p->scx.dsq_flags & SCX_TASK_DSQ_ON_PRIQ) || !RB_EMPTY_NODE(&p->scx.dsq_priq)); if (!is_rq_owned) { raw_spin_lock_nested(&dsq->lock, (enq_flags & SCX_ENQ_NESTED) ? SINGLE_DEPTH_NESTING : 0); if (unlikely(dsq->id == SCX_DSQ_INVALID)) { scx_error(sch, "attempting to dispatch to a destroyed dsq"); /* fall back to the global dsq */ raw_spin_unlock(&dsq->lock); dsq = find_global_dsq(sch, task_cpu(p)); raw_spin_lock(&dsq->lock); } } if (unlikely((dsq->id & SCX_DSQ_FLAG_BUILTIN) && (enq_flags & SCX_ENQ_DSQ_PRIQ))) { /* * SCX_DSQ_LOCAL and SCX_DSQ_GLOBAL DSQs always consume from * their FIFO queues. To avoid confusion and accidentally * starving vtime-dispatched tasks by FIFO-dispatched tasks, we * disallow any internal DSQ from doing vtime ordering of * tasks. */ scx_error(sch, "cannot use vtime ordering for built-in DSQs"); enq_flags &= ~SCX_ENQ_DSQ_PRIQ; } /* * @dsq is locked and @enq_flags is sanitized. Commit the carried slice * and vtime before the PRIQ insertion below reads the new dsq_vtime. */ if (enq_flags & SCX_ENQ_APPLY_SLICE) apply_slice_vtime(p, slice, vtime, enq_flags); if (enq_flags & SCX_ENQ_DSQ_PRIQ) { struct rb_node *rbp; /* * A PRIQ DSQ shouldn't be using FIFO enqueueing. As tasks are * linked to both the rbtree and list on PRIQs, this can only be * tested easily when adding the first task. */ if (unlikely(RB_EMPTY_ROOT(&dsq->priq) && nldsq_next_task(dsq, NULL, false))) scx_error(sch, "DSQ ID 0x%016llx already had FIFO-enqueued tasks", dsq->id); p->scx.dsq_flags |= SCX_TASK_DSQ_ON_PRIQ; rb_add(&p->scx.dsq_priq, &dsq->priq, scx_dsq_priq_less); /* * Find the previous task and insert after it on the list so * that @dsq->list is vtime ordered. */ rbp = rb_prev(&p->scx.dsq_priq); if (rbp) { struct task_struct *prev = container_of(rbp, struct task_struct, scx.dsq_priq); list_add(&p->scx.dsq_list.node, &prev->scx.dsq_list.node); /* first task unchanged - no update needed */ } else { list_add(&p->scx.dsq_list.node, &dsq->list); /* not builtin and new task is at head - use fastpath */ rcu_assign_pointer(dsq->first_task, p); } } else { /* a FIFO DSQ shouldn't be using PRIQ enqueuing */ if (unlikely(!RB_EMPTY_ROOT(&dsq->priq))) scx_error(sch, "DSQ ID 0x%016llx already had PRIQ-enqueued tasks", dsq->id); if (enq_flags & (SCX_ENQ_HEAD | SCX_ENQ_PREEMPT)) { /* new task inserted at head - use fastpath */ if (dsq_insert_head(dsq, p) && !(dsq->id & SCX_DSQ_FLAG_BUILTIN)) rcu_assign_pointer(dsq->first_task, p); } else { /* * dsq->list can contain parked BPF iterator cursors, so * list_empty() here isn't a reliable proxy for "no real * task in the DSQ". Test dsq->first_task directly. */ list_add_tail(&p->scx.dsq_list.node, &dsq->list); if (!dsq->first_task && !(dsq->id & SCX_DSQ_FLAG_BUILTIN)) rcu_assign_pointer(dsq->first_task, p); } } /* seq records the order tasks are queued, used by BPF DSQ iterator */ WRITE_ONCE(dsq->seq, dsq->seq + 1); p->scx.dsq_seq = dsq->seq; dsq_inc_nr(dsq, p, enq_flags); p->scx.dsq = dsq; /* * Update custody and call ops.dequeue() before clearing ops_state: * once ops_state is cleared, waiters in ops_dequeue() can proceed * and dequeue_task_scx() will RMW p->scx.flags. If we clear * ops_state first, both sides would modify p->scx.flags * concurrently in a non-atomic way. */ if (is_rq_owned) { rq_owned_post_enq(sch, rq, dsq, p, enq_flags); } else { /* * Global and bypass DSQs are terminal - the task leaves the * scheduler's custody, so ops.dequeue() fires here. It can run * without @p's rq lock (finish_dispatch() passes the dispatch * rq); that's safe because dequeue_task_scx() waits on * SCX_OPSS_DISPATCHING (see the ops_state note above) and so * can't race it. A non-terminal DSQ keeps the task in custody. */ if (dsq->id == SCX_DSQ_GLOBAL || dsq->id == SCX_DSQ_BYPASS) call_task_dequeue(sch, rq, p, 0); else p->scx.flags |= SCX_TASK_IN_CUSTODY; raw_spin_unlock(&dsq->lock); } /* * We're transitioning out of QUEUEING or DISPATCHING. store_release to * match waiters' load_acquire. */ if (enq_flags & SCX_ENQ_CLEAR_OPSS) atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE); } void scx_task_unlink_from_dsq(struct task_struct *p, struct scx_dispatch_q *dsq) { WARN_ON_ONCE(list_empty(&p->scx.dsq_list.node)); if (p->scx.dsq_flags & SCX_TASK_DSQ_ON_PRIQ) { rb_erase(&p->scx.dsq_priq, &dsq->priq); RB_CLEAR_NODE(&p->scx.dsq_priq); p->scx.dsq_flags &= ~SCX_TASK_DSQ_ON_PRIQ; } list_del_init(&p->scx.dsq_list.node); dsq_dec_nr(dsq, p); if (!(dsq->id & SCX_DSQ_FLAG_BUILTIN) && rcu_access_pointer(dsq->first_task) == p) { struct task_struct *first_task; first_task = nldsq_next_task(dsq, NULL, false); rcu_assign_pointer(dsq->first_task, first_task); } } void scx_dispatch_dequeue(struct rq *rq, struct task_struct *p) { struct scx_dispatch_q *dsq = p->scx.dsq; bool is_rq_owned = dsq && dsq_is_rq_owned(dsq); lockdep_assert_rq_held(rq); if (!dsq) { /* * If !dsq && on-list, @p is on @rq's ddsp_deferred_locals. * Unlinking is all that's needed to cancel. */ if (unlikely(!list_empty(&p->scx.dsq_list.node))) list_del_init(&p->scx.dsq_list.node); /* * When dispatching directly from the BPF scheduler to a local * DSQ, the task isn't associated with any DSQ but * @p->scx.holding_cpu may be set under the protection of * %SCX_OPSS_DISPATCHING. */ if (p->scx.holding_cpu >= 0) p->scx.holding_cpu = -1; return; } if (!is_rq_owned) raw_spin_lock(&dsq->lock); /* * Now that we hold @dsq->lock, @p->holding_cpu and @p->scx.dsq_* can't * change underneath us. */ if (p->scx.holding_cpu < 0) { /* @p must still be on @dsq, dequeue */ scx_task_unlink_from_dsq(p, dsq); } else { /* * We're racing against dispatch_to_local_dsq() which already * removed @p from @dsq and set @p->scx.holding_cpu. Clear the * holding_cpu which tells dispatch_to_local_dsq() that it lost * the race. */ WARN_ON_ONCE(!list_empty(&p->scx.dsq_list.node)); p->scx.holding_cpu = -1; } p->scx.dsq = NULL; if (!is_rq_owned) raw_spin_unlock(&dsq->lock); } /* * Abbreviated version of scx_dispatch_dequeue() that can be used when both * @p's rq and dsq are locked. */ static void dispatch_dequeue_locked(struct task_struct *p, struct scx_dispatch_q *dsq) { lockdep_assert_rq_held(task_rq(p)); lockdep_assert_held(&dsq->lock); scx_task_unlink_from_dsq(p, dsq); p->scx.dsq = NULL; } static struct scx_dispatch_q *find_dsq_for_dispatch(struct scx_sched *sch, struct rq *rq, u64 dsq_id, s32 tcpu) { struct scx_dispatch_q *dsq; if (dsq_id == SCX_DSQ_LOCAL) return &rq->scx.local_dsq; if ((dsq_id & SCX_DSQ_LOCAL_ON) == SCX_DSQ_LOCAL_ON) { s32 cpu = scx_cpu_ret(sch, dsq_id & SCX_DSQ_LOCAL_CPU_MASK); if (!scx_cpu_valid(sch, cpu, "in SCX_DSQ_LOCAL_ON dispatch verdict")) return find_global_dsq(sch, tcpu); return &cpu_rq(cpu)->scx.local_dsq; } if (dsq_id == SCX_DSQ_GLOBAL) dsq = find_global_dsq(sch, tcpu); else dsq = find_user_dsq(sch, dsq_id); /* * Built-in DSQs are never inserted into dsq_hash, so REJECT and RESCUE * hit the error below. They cannot be reached with an ID. */ if (unlikely(!dsq)) { scx_error(sch, "non-existent DSQ 0x%llx", dsq_id); return find_global_dsq(sch, tcpu); } return dsq; } static void mark_direct_dispatch(struct scx_sched *sch, struct task_struct *ddsp_task, struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) { /* * Mark that dispatch already happened from ops.select_cpu() or * ops.enqueue() by spoiling direct_dispatch_task with a non-NULL value * which can never match a valid task pointer. */ __this_cpu_write(direct_dispatch_task, ERR_PTR(-ESRCH)); /* @p must match the task on the enqueue path */ if (unlikely(p != ddsp_task)) { if (IS_ERR(ddsp_task)) scx_error(sch, "%s[%d] already direct-dispatched", p->comm, p->pid); else scx_error(sch, "scheduling for %s[%d] but trying to direct-dispatch %s[%d]", ddsp_task->comm, ddsp_task->pid, p->comm, p->pid); return; } WARN_ON_ONCE(p->scx.ddsp_dsq_id != SCX_DSQ_INVALID); WARN_ON_ONCE(p->scx.ddsp_enq_flags); p->scx.ddsp_slice = slice; p->scx.ddsp_vtime = vtime; p->scx.ddsp_dsq_id = dsq_id; p->scx.ddsp_enq_flags = enq_flags; } /* * Clear @p direct dispatch state when leaving the scheduler. * * Direct dispatch state must be cleared in the following cases: * - direct_dispatch(): cleared on the synchronous enqueue path, deferred * dispatch keeps the state until consumed * - process_ddsp_deferred_locals(): cleared after consuming deferred state, * - scx_do_enqueue_task(): cleared on enqueue fallbacks where the dispatch * verdict is ignored (local/global/bypass) * - dequeue_task_scx(): cleared after scx_dispatch_dequeue(), covering * deferred cancellation and holding_cpu races * - scx_disable_task(): cleared for queued wakeup tasks, which are excluded by * the scx_bypass() loop, so that stale state is not reused by a subsequent * scheduler instance */ static inline void clear_direct_dispatch(struct task_struct *p) { p->scx.ddsp_dsq_id = SCX_DSQ_INVALID; p->scx.ddsp_enq_flags = 0; } static void direct_dispatch(struct scx_sched *sch, struct task_struct *p, u64 enq_flags) { struct rq *rq = task_rq(p); struct scx_dispatch_q *dsq = find_dsq_for_dispatch(sch, rq, p->scx.ddsp_dsq_id, task_cpu(p)); u64 ddsp_enq_flags, slice, vtime; p->scx.ddsp_enq_flags |= enq_flags; /* * We are in the enqueue path with @rq locked and pinned, and thus can't * double lock a remote rq and enqueue to its local DSQ. For * DSQ_LOCAL_ON verdicts targeting the local DSQ of a remote CPU, defer * the enqueue so that it's executed when @rq can be unlocked. */ if (dsq->id == SCX_DSQ_LOCAL && dsq != &rq->scx.local_dsq) { unsigned long opss; opss = atomic_long_read(&p->scx.ops_state) & SCX_OPSS_STATE_MASK; switch (opss & SCX_OPSS_STATE_MASK) { case SCX_OPSS_NONE: break; case SCX_OPSS_QUEUEING: /* * As @p was never passed to the BPF side, _release is * not strictly necessary. Still do it for consistency. */ atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE); break; default: WARN_ONCE(true, "sched_ext: %s[%d] has invalid ops state 0x%lx in direct_dispatch()", p->comm, p->pid, opss); atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE); break; } WARN_ON_ONCE(p->scx.dsq || !list_empty(&p->scx.dsq_list.node)); list_add_tail(&p->scx.dsq_list.node, &rq->scx.ddsp_deferred_locals); schedule_deferred_locked(rq); return; } ddsp_enq_flags = p->scx.ddsp_enq_flags; slice = p->scx.ddsp_slice; vtime = p->scx.ddsp_vtime; clear_direct_dispatch(p); scx_dispatch_enqueue(sch, rq, dsq, p, slice, vtime, ddsp_enq_flags | SCX_ENQ_APPLY_SLICE | SCX_ENQ_CLEAR_OPSS); } bool scx_rq_online(struct rq *rq) { /* * Test both cpu_active() and %SCX_RQ_ONLINE. %SCX_RQ_ONLINE indicates * the online state as seen from the BPF scheduler. cpu_active() test * guarantees that, if this function returns %true, %SCX_RQ_ONLINE will * stay set until the current scheduling operation is complete even if * we aren't locking @rq. */ return likely((rq->scx.flags & SCX_RQ_ONLINE) && cpu_active(cpu_of(rq))); } void scx_do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags, int sticky_cpu) { struct scx_sched *sch = scx_task_sched(p); struct task_struct **ddsp_taskp; struct scx_dispatch_q *dsq; unsigned long qseq; WARN_ON_ONCE(!(p->scx.flags & SCX_TASK_QUEUED)); /* internal movements - rq migration / RESTORE */ if (sticky_cpu == cpu_of(rq)) goto local_norefill; /* * Clear persistent TASK_IMMED for fresh enqueues, see dsq_inc_nr(). * Note that exiting and migration-disabled tasks that skip * ops.enqueue() below will lose IMMED protection unless * %SCX_OPS_ENQ_EXITING / %SCX_OPS_ENQ_MIGRATION_DISABLED are set. */ p->scx.flags &= ~SCX_TASK_IMMED; /* * A task reenqueued too many times without running means the scheduler * keeps re-deciding a placement it can't honor, e.g. re-inserting to a * cid it lacks caps on. Eject the owning scheduler and strand the task * to be picked up during sched exit. */ if (enq_flags & SCX_ENQ_REENQ) { if (++p->scx.reenq_cnt > 1) __scx_add_event(sch, SCX_EV_REENQ_REPEAT, 1); if (unlikely(p->scx.reenq_cnt > SCX_REENQ_MAX_REPEAT)) { __scx_exit(sch, SCX_EXIT_ERROR_REENQ, 0, cpu_of(rq), "%s[%d] reenqueued %u times without running", p->comm, p->pid, p->scx.reenq_cnt); return; } } /* * If !scx_rq_online(), we already told the BPF scheduler that the CPU * is offline and are just running the hotplug path. Don't bother the * BPF scheduler. */ if (!scx_rq_online(rq)) goto local; if (scx_bypassing(sch, cpu_of(rq))) { __scx_add_event(sch, SCX_EV_BYPASS_DISPATCH, 1); goto bypass; } if (p->scx.ddsp_dsq_id != SCX_DSQ_INVALID) goto direct; /* see %SCX_OPS_ENQ_EXITING */ if (!(sch->ops.flags & SCX_OPS_ENQ_EXITING) && unlikely(p->flags & PF_EXITING)) { __scx_add_event(sch, SCX_EV_ENQ_SKIP_EXITING, 1); enq_flags |= SCX_ENQ_RESCUE; /* avoid looping on cap rejection */ goto local; } /* see %SCX_OPS_ENQ_MIGRATION_DISABLED */ if (!(sch->ops.flags & SCX_OPS_ENQ_MIGRATION_DISABLED) && is_migration_disabled(p)) { __scx_add_event(sch, SCX_EV_ENQ_SKIP_MIGRATION_DISABLED, 1); goto local; } if (unlikely(!SCX_HAS_OP(sch, enqueue))) goto global; /* DSQ bypass didn't trigger, enqueue on the BPF scheduler */ qseq = rq->scx.ops_qseq++ << SCX_OPSS_QSEQ_SHIFT; WARN_ON_ONCE(atomic_long_read(&p->scx.ops_state) != SCX_OPSS_NONE); atomic_long_set(&p->scx.ops_state, SCX_OPSS_QUEUEING | qseq); ddsp_taskp = this_cpu_ptr(&direct_dispatch_task); WARN_ON_ONCE(*ddsp_taskp); *ddsp_taskp = p; SCX_CALL_OP_TASK(sch, enqueue, rq, p, enq_flags); *ddsp_taskp = NULL; if (p->scx.ddsp_dsq_id != SCX_DSQ_INVALID) goto direct; /* * Task is now in BPF scheduler's custody. Set %SCX_TASK_IN_CUSTODY * so ops.dequeue() is called when it leaves custody. */ p->scx.flags |= SCX_TASK_IN_CUSTODY; /* * If not directly dispatched, QUEUEING isn't clear yet and dispatch or * dequeue may be waiting. The store_release matches their load_acquire. */ atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_QUEUED | qseq); return; direct: direct_dispatch(sch, p, enq_flags); return; local_norefill: scx_dispatch_enqueue(sch, rq, &rq->scx.local_dsq, p, 0, 0, enq_flags); return; local: dsq = &rq->scx.local_dsq; goto enqueue; global: dsq = find_global_dsq(sch, task_cpu(p)); goto enqueue; bypass: dsq = bypass_enq_target_dsq(sch, task_cpu(p)); goto enqueue; enqueue: refill_task_slice_dfl(sch, p); clear_direct_dispatch(p); scx_dispatch_enqueue(sch, rq, dsq, p, 0, 0, enq_flags); } static bool task_runnable(const struct task_struct *p) { return !list_empty(&p->scx.runnable_node); } static void set_task_runnable(struct rq *rq, struct task_struct *p) { lockdep_assert_rq_held(rq); if (p->scx.flags & SCX_TASK_RESET_RUNNABLE_AT) { p->scx.runnable_at = jiffies; p->scx.flags &= ~SCX_TASK_RESET_RUNNABLE_AT; } /* * list_add_tail() must be used. scx_bypass() depends on tasks being * appended to the runnable_list. */ list_add_tail(&p->scx.runnable_node, &rq->scx.runnable_list); /* * Record the rq @p is runnable on, maintained under the rq lock so it * stays valid unlike task_cpu(), which a remote wakeup can move under * pi_lock alone. */ WRITE_ONCE(p->scx.runnable_cpu, cpu_of(rq)); } static void clr_task_runnable(struct task_struct *p, bool reset_runnable_at) { list_del_init(&p->scx.runnable_node); WRITE_ONCE(p->scx.runnable_cpu, -1); if (reset_runnable_at) { p->scx.flags |= SCX_TASK_RESET_RUNNABLE_AT; p->scx.reenq_cnt = 0; } } static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int core_enq_flags) { struct scx_sched *sch = scx_task_sched(p); int sticky_cpu = p->scx.sticky_cpu; u64 enq_flags = core_enq_flags | rq->scx.remote_activate_enq_flags; if (enq_flags & ENQUEUE_WAKEUP) rq->scx.flags |= SCX_RQ_IN_WAKEUP; /* * Restoring a running task will be immediately followed by * set_next_task_scx() which expects the task to not be on the BPF * scheduler as tasks can only start running through local DSQs. Force * direct-dispatch into the local DSQ by setting the sticky_cpu. Mark * IGNORE_CAPS to force entry into the local DSQ. */ if (unlikely(enq_flags & ENQUEUE_RESTORE) && task_current(rq, p)) { sticky_cpu = cpu_of(rq); enq_flags |= SCX_ENQ_IGNORE_CAPS; } if (p->scx.flags & SCX_TASK_QUEUED) { WARN_ON_ONCE(!task_runnable(p)); goto out; } set_task_runnable(rq, p); p->scx.flags |= SCX_TASK_QUEUED; rq->scx.nr_running++; add_nr_running(rq, 1); if (SCX_HAS_OP(sch, runnable) && !task_on_rq_migrating(p)) SCX_CALL_OP_TASK(sch, runnable, rq, p, enq_flags); /* Start dl_server if this is the first task being enqueued */ if (rq->scx.nr_running == 1) dl_server_start(&rq->ext_server); scx_do_enqueue_task(rq, p, enq_flags, sticky_cpu); if (sticky_cpu >= 0) p->scx.sticky_cpu = -1; out: rq->scx.flags &= ~SCX_RQ_IN_WAKEUP; if ((enq_flags & SCX_ENQ_CPU_SELECTED) && unlikely(cpu_of(rq) != p->scx.selected_cpu)) __scx_add_event(sch, SCX_EV_SELECT_CPU_FALLBACK, 1); } static void ops_dequeue(struct rq *rq, struct task_struct *p, u64 deq_flags) { struct scx_sched *sch = scx_task_sched(p); unsigned long opss; /* dequeue is always temporary, don't reset runnable_at */ clr_task_runnable(p, false); retry: /* acquire ensures that we see the preceding updates on QUEUED */ opss = atomic_long_read_acquire(&p->scx.ops_state); switch (opss & SCX_OPSS_STATE_MASK) { case SCX_OPSS_NONE: break; case SCX_OPSS_QUEUEING: /* * QUEUEING is started and finished while holding @p's rq lock. * As we're holding the rq lock now, we shouldn't see QUEUEING. */ BUG(); case SCX_OPSS_QUEUED: /* * A queued task must always be in BPF scheduler's custody. If * SCX_TASK_IN_CUSTODY is clear, finish_dispatch() on another * CPU has already passed call_task_dequeue() (which clears the * flag), but has not yet written SCX_OPSS_NONE. That final * store does not require this rq's lock, so retrying with * cpu_relax() is bounded: we will observe NONE (or DISPATCHING, * handled by the fallthrough) on a subsequent iteration. */ if (unlikely(!(READ_ONCE(p->scx.flags) & SCX_TASK_IN_CUSTODY))) { cpu_relax(); goto retry; } if (atomic_long_try_cmpxchg(&p->scx.ops_state, &opss, SCX_OPSS_NONE)) break; fallthrough; case SCX_OPSS_DISPATCHING: /* * If @p is being dispatched from the BPF scheduler to a DSQ, * wait for the transfer to complete so that @p doesn't get * added to its DSQ after dequeueing is complete. * * As we're waiting on DISPATCHING with the rq locked, the * dispatching side shouldn't try to lock the rq while * DISPATCHING is set. See dispatch_to_local_dsq(). * * DISPATCHING shouldn't have qseq set and control can reach * here with NONE @opss from the above QUEUED case block. * Explicitly wait on %SCX_OPSS_DISPATCHING instead of @opss. */ wait_ops_state(p, SCX_OPSS_DISPATCHING); BUG_ON(atomic_long_read(&p->scx.ops_state) != SCX_OPSS_NONE); break; } /* * Call ops.dequeue() if the task is still in BPF custody. * * The code that clears ops_state to %SCX_OPSS_NONE does not always * clear %SCX_TASK_IN_CUSTODY: in dispatch_to_local_dsq(), when * we're moving a task that was in %SCX_OPSS_DISPATCHING to a * remote CPU's local DSQ, we only set ops_state to %SCX_OPSS_NONE * so that a concurrent dequeue can proceed, but we clear * %SCX_TASK_IN_CUSTODY only when we later enqueue or move the * task. So we can see NONE + IN_CUSTODY here and we must handle * it. Similarly, after waiting on %SCX_OPSS_DISPATCHING we see * NONE but the task may still have %SCX_TASK_IN_CUSTODY set until * it is enqueued on the destination. */ call_task_dequeue(sch, rq, p, deq_flags); } static bool dequeue_task_scx(struct rq *rq, struct task_struct *p, int core_deq_flags) { struct scx_sched *sch = scx_task_sched(p); u64 deq_flags = core_deq_flags; /* * Set %SCX_DEQ_SCHED_CHANGE when the dequeue is due to a property * change (not sleep). */ if (!(deq_flags & DEQUEUE_SLEEP)) deq_flags |= SCX_DEQ_SCHED_CHANGE; if (!(p->scx.flags & SCX_TASK_QUEUED)) { WARN_ON_ONCE(task_runnable(p)); return true; } ops_dequeue(rq, p, deq_flags); /* * A currently running task which is going off @rq first gets dequeued * and then stops running. As we want running <-> stopping transitions * to be contained within runnable <-> quiescent transitions, trigger * ->stopping() early here instead of in put_prev_task_scx(). * * @p may go through multiple stopping <-> running transitions between * here and put_prev_task_scx() if task attribute changes occur while * dispatch_one() leaves @rq unlocked. However, they don't contain any * information meaningful to the BPF scheduler and can be suppressed by * skipping the callbacks if the task is !QUEUED. */ if (task_current(rq, p) && (SCX_HAS_OP(sch, stopping) || unlikely(p == scx_rescuee(rq)))) { update_curr_scx(rq); if (SCX_HAS_OP(sch, stopping)) SCX_CALL_OP_TASK(sch, stopping, rq, p, false); } if (SCX_HAS_OP(sch, quiescent) && !task_on_rq_migrating(p)) SCX_CALL_OP_TASK(sch, quiescent, rq, p, deq_flags); if (deq_flags & SCX_DEQ_SLEEP) p->scx.flags |= SCX_TASK_DEQD_FOR_SLEEP; else p->scx.flags &= ~SCX_TASK_DEQD_FOR_SLEEP; p->scx.flags &= ~SCX_TASK_QUEUED; rq->scx.nr_running--; sub_nr_running(rq, 1); scx_dispatch_dequeue(rq, p); /* see scx_task_slice_ended() for the save/restore exception */ if (!((deq_flags & DEQUEUE_SAVE) && task_current(rq, p))) scx_task_slice_ended(rq, p); clear_direct_dispatch(p); return true; } static void yield_task_scx(struct rq *rq) { struct task_struct *p = rq->donor; struct scx_sched *sch = scx_task_sched(p); /* a yield gives the slice up */ scx_task_slice_ended(rq, p); if (SCX_HAS_OP(sch, yield)) SCX_CALL_OP_2TASKS_RET(sch, yield, rq, p, NULL); else scx_set_task_slice(p, 0); } static bool yield_to_task_scx(struct rq *rq, struct task_struct *to) { struct task_struct *from = rq->donor; struct scx_sched *sch = scx_task_sched(from); /* like a plain yield, giving the slice up ends the protection */ scx_task_slice_ended(rq, from); if (SCX_HAS_OP(sch, yield) && sch == scx_task_sched(to)) return SCX_CALL_OP_2TASKS_RET(sch, yield, rq, from, to); else return false; } static void wakeup_preempt_scx(struct rq *rq, struct task_struct *p, int wake_flags) { /* * Preemption between SCX tasks is implemented by resetting the victim * task's slice to 0 and triggering reschedule on the target CPU. * Nothing to do. */ if (p->sched_class == &ext_sched_class) return; /* * Getting preempted by a higher-priority class. Reenqueue IMMED tasks. * This captures all preemption cases including: * * - A SCX task is currently running. * * - @rq is waking from idle due to a SCX task waking to it. * * - A higher-priority wakes up while SCX dispatch is in progress. */ if (rq->scx.nr_immed) scx_schedule_reenq_local(rq, 0); } void scx_move_local_task_to_local_dsq(struct scx_sched *sch, struct task_struct *p, u64 enq_flags, struct scx_dispatch_q *src_dsq, struct rq *dst_rq) { struct scx_dispatch_q *dst_dsq = scx_resolve_local_dsq(sch, dst_rq, p, &enq_flags); /* @p is on @dst_rq, an rq-owned @src_dsq is covered by the rq lock */ if (!dsq_is_rq_owned(src_dsq)) lockdep_assert_held(&src_dsq->lock); lockdep_assert_rq_held(dst_rq); WARN_ON_ONCE(p->scx.holding_cpu >= 0); if (enq_flags & (SCX_ENQ_HEAD | SCX_ENQ_PREEMPT)) dsq_insert_head(dst_dsq, p); else list_add_tail(&p->scx.dsq_list.node, &dst_dsq->list); dsq_inc_nr(dst_dsq, p, enq_flags); p->scx.dsq = dst_dsq; rq_owned_post_enq(sch, dst_rq, dst_dsq, p, enq_flags); } /** * move_remote_task_to_local_dsq - Move a task from a foreign rq to a local DSQ * @sch: scheduler placing @p * @p: task to move * @enq_flags: %SCX_ENQ_* * @src_rq: rq to move the task from, locked on entry, released on return * @dst_rq: rq to move the task into, locked on return * * Move @p which is currently on @src_rq to @dst_rq's local DSQ. */ static void move_remote_task_to_local_dsq(struct scx_sched *sch, struct task_struct *p, u64 enq_flags, struct rq *src_rq, struct rq *dst_rq) { lockdep_assert_rq_held(src_rq); /* * Set sticky_cpu before deactivate_task() to properly mark the * beginning of an SCX-internal migration. */ p->scx.sticky_cpu = cpu_of(dst_rq); deactivate_task(src_rq, p, 0); set_task_cpu(p, cpu_of(dst_rq)); switch_rq_lock(src_rq, dst_rq); /* * activate_task() below truncates enq_flags to 32 bits and re-derives * @p's owner, dropping our scx flags and the placing @sch. We own @rq, * so stash both across the call. The enqueue reads them back, keeping * the scx flags and checking caps against the placer, not the owner. */ WARN_ON_ONCE(!cpumask_test_cpu(cpu_of(dst_rq), p->cpus_ptr)); WARN_ON_ONCE(dst_rq->scx.remote_activate_enq_flags || dst_rq->scx.remote_activate_sch); dst_rq->scx.remote_activate_enq_flags = enq_flags; dst_rq->scx.remote_activate_sch = sch; activate_task(dst_rq, p, 0); dst_rq->scx.remote_activate_enq_flags = 0; dst_rq->scx.remote_activate_sch = NULL; } /* * Similar to kernel/sched/core.c::is_cpu_allowed(). However, there are two * differences: * * - is_cpu_allowed() asks "Can this task run on this CPU?" while * task_can_run_on_remote_rq() asks "Can the BPF scheduler migrate the task to * this CPU?". * * While migration is disabled, is_cpu_allowed() has to say "yes" as the task * must be allowed to finish on the CPU that it's currently on regardless of * the CPU state. However, task_can_run_on_remote_rq() must say "no" as the * BPF scheduler shouldn't attempt to migrate a task which has migration * disabled. * * - The BPF scheduler is bypassed while the rq is offline and we can always say * no to the BPF scheduler initiated migrations while offline. * * The caller must ensure that @p and @rq are on different CPUs. * If enforce == true, caller must hold @p's rq lock. */ static bool task_can_run_on_remote_rq(struct scx_sched *sch, struct task_struct *p, struct rq *rq, bool enforce) { s32 cpu = cpu_of(rq); /* * To prevent races with @p still running on its old CPU while switching * out, make sure we're holding @p's rq lock so as not to risk * erroneously killing the BPF scheduler. */ if (enforce) lockdep_assert_rq_held(task_rq(p)); WARN_ON_ONCE(task_cpu(p) == cpu); /* * If @p has migration disabled, @p->cpus_ptr is updated to contain only * the pinned CPU in migrate_disable_switch() while @p is being switched * out. However, put_prev_task_scx() is called before @p->cpus_ptr is * updated and thus another CPU may see @p on a DSQ inbetween leading to * @p passing the below task_allowed_on_cpu() check while migration is * disabled. * * Test the migration disabled state first as the race window is narrow * and the BPF scheduler failing to check migration disabled state can * easily be masked if task_allowed_on_cpu() is done first. */ if (unlikely(is_migration_disabled(p))) { if (enforce) scx_error(sch, "SCX_DSQ_LOCAL[_ON] cannot move migration disabled %s[%d] from CPU %d to %d", p->comm, p->pid, task_cpu(p), cpu); return false; } /* * We don't require the BPF scheduler to avoid dispatching to offline * CPUs mostly for convenience but also because CPUs can go offline * between scx_bpf_dsq_insert() calls and here. Trigger error iff the * picked CPU is outside the allowed mask. */ if (!task_allowed_on_cpu(p, cpu)) { if (enforce) scx_error(sch, "SCX_DSQ_LOCAL[_ON] target CPU %d not allowed for %s[%d]", cpu, p->comm, p->pid); return false; } if (!scx_rq_online(rq)) { if (enforce) __scx_add_event(sch, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE, 1); return false; } return true; } /** * unlink_dsq_and_switch_rq_lock() - Unlink task and switch to its rq lock * @p: target task * @dsq: locked DSQ @p is currently on * @locked_rq: currently locked rq * @src_rq: rq @p is currently on, stable with @dsq locked * * Called with @dsq and @locked_rq locked. We want to move @p to a different DSQ, * including any local DSQ, but are not locking @src_rq. Locking @src_rq is * required when transferring into a local DSQ. Even when transferring into a * non-local DSQ, it's better to use the same mechanism to protect against * dequeues and maintain the invariant that @p->scx.dsq can only change while * @src_rq is locked, which e.g. scx_dump_task() depends on. * * We want to grab @src_rq but that can deadlock if we try while locking @dsq, * so we want to unlink @p from @dsq, drop its lock and then lock @src_rq. As * this may race with dequeue, which can't drop the rq lock or fail, do a little * dancing from our side. * * @p->scx.holding_cpu is set to this CPU before @dsq is unlocked. If @p gets * dequeued after we unlock @dsq but before locking @src_rq, the holding_cpu * would be cleared to -1. While other cpus may have updated it to different * values afterwards, as this operation can't be preempted or recurse, the * holding_cpu can never become this CPU again before we're done. Thus, we can * tell whether we lost to dequeue by testing whether the holding_cpu still * points to this CPU. See scx_dispatch_dequeue() for the counterpart. * * On return, @dsq is unlocked and @src_rq is locked. Returns %true if @p is * still valid. %false if lost to dequeue. */ static bool unlink_dsq_and_switch_rq_lock(struct task_struct *p, struct scx_dispatch_q *dsq, struct rq *locked_rq, struct rq *src_rq) { s32 cpu = raw_smp_processor_id(); lockdep_assert_held(&dsq->lock); lockdep_assert_rq_held(locked_rq); WARN_ON_ONCE(p->scx.holding_cpu >= 0); scx_task_unlink_from_dsq(p, dsq); p->scx.holding_cpu = cpu; raw_spin_unlock(&dsq->lock); switch_rq_lock(locked_rq, src_rq); /* task_rq couldn't have changed if we're still the holding cpu */ return likely(p->scx.holding_cpu == cpu) && !WARN_ON_ONCE(src_rq != task_rq(p)); } static bool consume_remote_task(struct scx_sched *sch, struct rq *this_rq, struct task_struct *p, u64 enq_flags, struct scx_dispatch_q *dsq, struct rq *src_rq) { if (unlink_dsq_and_switch_rq_lock(p, dsq, this_rq, src_rq)) { move_remote_task_to_local_dsq(sch, p, enq_flags, src_rq, this_rq); return true; } else { switch_rq_lock(src_rq, this_rq); return false; } } /** * move_task_between_dsqs() - Move a task from one DSQ to another * @sch: scx_sched being operated on * @p: target task * @enq_flags: %SCX_ENQ_* * @src_dsq: DSQ @p is currently on, must not be a local DSQ * @dst_dsq: DSQ @p is being moved to, can be any DSQ * * Must be called with @p's task_rq and @src_dsq locked. If @dst_dsq is a local * DSQ and @p is on a different CPU, @p will be migrated and thus its task_rq * will change. As @p's task_rq is locked, this function doesn't need to use the * holding_cpu mechanism. * * On return, @src_dsq is unlocked and only @p's new task_rq, which is the * return value, is locked. */ static struct rq *move_task_between_dsqs(struct scx_sched *sch, struct task_struct *p, u64 enq_flags, struct scx_dispatch_q *src_dsq, struct scx_dispatch_q *dst_dsq) { struct rq *src_rq = task_rq(p), *dst_rq; BUG_ON(src_dsq->id == SCX_DSQ_LOCAL); lockdep_assert_held(&src_dsq->lock); lockdep_assert_rq_held(src_rq); if (dst_dsq->id == SCX_DSQ_LOCAL) { dst_rq = container_of(dst_dsq, struct rq, scx.local_dsq); if (src_rq != dst_rq && unlikely(!task_can_run_on_remote_rq(sch, p, dst_rq, true))) { dst_dsq = find_global_dsq(sch, task_cpu(p)); dst_rq = src_rq; enq_flags |= SCX_ENQ_GDSQ_FALLBACK; } } else { /* no need to migrate if destination is a non-local DSQ */ dst_rq = src_rq; } /* * Move @p into $dst_dsq. If $dst_dsq is the local DSQ of a different * CPU, @p will be migrated. */ if (dst_dsq->id == SCX_DSQ_LOCAL) { /* @p is going from a non-local DSQ to a local DSQ */ if (src_rq == dst_rq) { scx_task_unlink_from_dsq(p, src_dsq); scx_move_local_task_to_local_dsq(sch, p, enq_flags, src_dsq, dst_rq); raw_spin_unlock(&src_dsq->lock); } else { raw_spin_unlock(&src_dsq->lock); move_remote_task_to_local_dsq(sch, p, enq_flags, src_rq, dst_rq); } } else { /* * @p is going from a non-local DSQ to a non-local DSQ. As * $src_dsq is already locked, do an abbreviated dequeue. */ dispatch_dequeue_locked(p, src_dsq); raw_spin_unlock(&src_dsq->lock); scx_dispatch_enqueue(sch, dst_rq, dst_dsq, p, 0, 0, enq_flags); } return dst_rq; } bool scx_consume_dispatch_q(struct scx_sched *sch, struct rq *rq, struct scx_dispatch_q *dsq, u64 enq_flags) { struct task_struct *p; retry: /* * The caller can't expect to successfully consume a task if the task's * addition to @dsq isn't guaranteed to be visible somehow. Test * @dsq->list without locking and skip if it seems empty. */ if (list_empty(&dsq->list)) return false; raw_spin_lock(&dsq->lock); nldsq_for_each_task(p, dsq) { struct rq *task_rq = task_rq(p); /* * This loop can lead to multiple lockup scenarios, e.g. the BPF * scheduler can put an enormous number of affinitized tasks into * a contended DSQ, or the outer retry loop can repeatedly race * against scx_bypass() dequeueing tasks from @dsq trying to put * the system into the bypass mode. This can easily live-lock the * machine. If aborting, exit from all non-bypass DSQs. */ if (unlikely(READ_ONCE(sch->aborting)) && dsq->id != SCX_DSQ_BYPASS) break; if (rq == task_rq) { scx_task_unlink_from_dsq(p, dsq); scx_move_local_task_to_local_dsq(sch, p, enq_flags, dsq, rq); raw_spin_unlock(&dsq->lock); return true; } if (task_can_run_on_remote_rq(sch, p, rq, false)) { if (likely(consume_remote_task(sch, rq, p, enq_flags, dsq, task_rq))) return true; goto retry; } } raw_spin_unlock(&dsq->lock); return false; } bool scx_consume_global_dsq(struct scx_sched *sch, struct rq *rq) { int node = cpu_to_node(cpu_of(rq)); return scx_consume_dispatch_q(sch, rq, &sch->pnode[node]->global_dsq, 0); } /** * dispatch_to_local_dsq - Dispatch a task to a local dsq * @sch: scx_sched being operated on * @rq: current rq which is locked * @dst_dsq: destination DSQ * @p: task to dispatch * @slice: slice carried by the insert verdict, 0 keeps the current value * @vtime: vtime carried by the insert verdict, committed on PRIQ inserts * @enq_flags: %SCX_ENQ_* * * We're holding @rq lock and want to dispatch @p to @dst_dsq which is a local * DSQ. This function performs all the synchronization dancing needed because * local DSQs are protected with rq locks. * * The caller must have exclusive ownership of @p (e.g. through * %SCX_OPSS_DISPATCHING). */ static void dispatch_to_local_dsq(struct scx_sched *sch, struct rq *rq, struct scx_dispatch_q *dst_dsq, struct task_struct *p, u64 slice, u64 vtime, u64 enq_flags) { struct rq *src_rq = task_rq(p); struct rq *dst_rq = container_of(dst_dsq, struct rq, scx.local_dsq); struct rq *locked_rq = rq; /* * We're synchronized against dequeue through DISPATCHING. As @p can't * be dequeued, its task_rq and cpus_allowed are stable too. * * If dispatching to @rq that @p is already on, no lock dancing needed. */ if (rq == src_rq && rq == dst_rq) { scx_dispatch_enqueue(sch, rq, dst_dsq, p, slice, vtime, enq_flags | SCX_ENQ_APPLY_SLICE | SCX_ENQ_CLEAR_OPSS); return; } /* * @p is on a possibly remote @src_rq which we need to lock to move the * task. If dequeue is in progress, it'd be locking @src_rq and waiting * on DISPATCHING, so we can't grab @src_rq lock while holding * DISPATCHING. * * As DISPATCHING guarantees that @p is wholly ours, we can pretend that * we're moving from a DSQ and use the same mechanism - mark the task * under transfer with holding_cpu, release DISPATCHING and then follow * the same protocol. See unlink_dsq_and_switch_rq_lock(). */ p->scx.holding_cpu = raw_smp_processor_id(); /* store_release ensures that dequeue sees the above */ atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE); /* switch to @src_rq lock */ if (locked_rq != src_rq) { switch_rq_lock(locked_rq, src_rq); locked_rq = src_rq; } /* task_rq couldn't have changed if we're still the holding cpu */ if (likely(p->scx.holding_cpu == raw_smp_processor_id()) && !WARN_ON_ONCE(src_rq != task_rq(p))) { bool fallback = false; /* * If @p is staying on the same rq, there's no need to go * through the full deactivate/activate cycle. Optimize by * abbreviating move_remote_task_to_local_dsq(). */ if (src_rq == dst_rq) { p->scx.holding_cpu = -1; scx_dispatch_enqueue(sch, dst_rq, &dst_rq->scx.local_dsq, p, slice, vtime, enq_flags | SCX_ENQ_APPLY_SLICE); } else if (unlikely(!task_can_run_on_remote_rq(sch, p, dst_rq, true))) { p->scx.holding_cpu = -1; fallback = true; scx_dispatch_enqueue(sch, src_rq, find_global_dsq(sch, task_cpu(p)), p, slice, vtime, enq_flags | SCX_ENQ_APPLY_SLICE | SCX_ENQ_GDSQ_FALLBACK); } else { apply_slice_vtime(p, slice, vtime, enq_flags); move_remote_task_to_local_dsq(sch, p, enq_flags, src_rq, dst_rq); /* task has been moved to dst_rq, which is now locked */ locked_rq = dst_rq; } /* if the destination CPU is idle, wake it up */ if (!fallback && sched_class_above(p->sched_class, dst_rq->curr->sched_class)) resched_curr(dst_rq); } /* switch back to @rq lock */ if (locked_rq != rq) switch_rq_lock(locked_rq, rq); } /** * finish_dispatch - Asynchronously finish dispatching a task * @sch: the scheduler * @rq: current rq which is locked * @p: task to finish dispatching * @qseq_at_dispatch: qseq when @p started getting dispatched * @dsq_id: destination DSQ ID * @enq_flags: %SCX_ENQ_* * * Dispatching to local DSQs may need to wait for queueing to complete or * require rq lock dancing. As we don't wanna do either while inside * ops.dispatch() to avoid locking order inversion, we split dispatching into * two parts. scx_bpf_dsq_insert() which is called by ops.dispatch() records the * task and its qseq. Once ops.dispatch() returns, this function is called to * finish up. * * There is no guarantee that @p is still valid for dispatching or even that it * was valid in the first place. Make sure that the task is still owned by the * BPF scheduler and claim the ownership before dispatching. */ static void finish_dispatch(struct scx_sched *sch, struct rq *rq, struct task_struct *p, unsigned long qseq_at_dispatch, u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) { struct scx_dispatch_q *dsq; unsigned long opss; retry: /* * No need for _acquire here. @p is accessed only after a successful * try_cmpxchg to DISPATCHING. */ opss = atomic_long_read(&p->scx.ops_state); switch (opss & SCX_OPSS_STATE_MASK) { case SCX_OPSS_DISPATCHING: case SCX_OPSS_NONE: /* someone else already got to it */ return; case SCX_OPSS_QUEUED: /* * If qseq doesn't match, @p has gone through at least one * dispatch/dequeue and re-enqueue cycle between * scx_bpf_dsq_insert() and here and we have no claim on it. */ if ((opss & SCX_OPSS_QSEQ_MASK) != qseq_at_dispatch) return; /* see SCX_EV_INSERT_NOT_OWNED definition */ if (unlikely(!scx_task_on_sched(sch, p))) { __scx_add_event(sch, SCX_EV_INSERT_NOT_OWNED, 1); return; } /* * While we know @p is accessible, we don't yet have a claim on * it - the BPF scheduler is allowed to dispatch tasks * spuriously and there can be a racing dequeue attempt. Let's * claim @p by atomically transitioning it from QUEUED to * DISPATCHING. */ if (likely(atomic_long_try_cmpxchg(&p->scx.ops_state, &opss, SCX_OPSS_DISPATCHING))) break; goto retry; case SCX_OPSS_QUEUEING: /* * scx_do_enqueue_task() is in the process of transferring the * task to the BPF scheduler while holding @p's rq lock. As we * aren't holding any kernel or BPF resource that the enqueue * path may depend upon, it's safe to wait. */ wait_ops_state(p, opss); goto retry; } BUG_ON(!(p->scx.flags & SCX_TASK_QUEUED)); dsq = find_dsq_for_dispatch(sch, rq, dsq_id, task_cpu(p)); if (dsq->id == SCX_DSQ_LOCAL) dispatch_to_local_dsq(sch, rq, dsq, p, slice, vtime, enq_flags); else scx_dispatch_enqueue(sch, rq, dsq, p, slice, vtime, enq_flags | SCX_ENQ_APPLY_SLICE | SCX_ENQ_CLEAR_OPSS); } void scx_flush_dispatch_buf(struct scx_sched *sch, struct rq *rq) { struct scx_dsp_ctx *dspc = &this_cpu_ptr(sch->pcpu)->dsp_ctx; u32 u; for (u = 0; u < dspc->cursor; u++) { struct scx_dsp_buf_ent *ent = &dspc->buf[u]; finish_dispatch(sch, rq, ent->task, ent->qseq, ent->dsq_id, ent->slice, ent->vtime, ent->enq_flags); } dspc->nr_tasks += dspc->cursor; dspc->cursor = 0; } static inline void maybe_queue_balance_callback(struct rq *rq) { lockdep_assert_rq_held(rq); if (!(rq->scx.flags & SCX_RQ_BAL_CB_PENDING)) return; queue_balance_callback(rq, &rq->scx.deferred_bal_cb, deferred_bal_cb_workfn); rq->scx.flags &= ~SCX_RQ_BAL_CB_PENDING; } static enum scx_dsp_verdict dispatch_one(struct rq *rq, struct task_struct *prev) { struct scx_sched *sch = scx_root_protected_live(); enum scx_dsp_verdict verdict; s32 cpu = cpu_of(rq); lockdep_assert_rq_held(rq); rq->scx.flags |= SCX_RQ_IN_DISPATCH; scx_process_sync_ecaps(rq, prev); if ((sch->ops.flags & SCX_OPS_HAS_CPU_PREEMPT) && unlikely(rq->scx.cpu_released)) { /* * If the previous sched_class for the current CPU was not SCX, * notify the BPF scheduler that it again has control of the * core. This callback complements ->cpu_release(), which is * emitted in switch_class(). */ if (sch->ops.cpu_acquire) SCX_CALL_OP(sch, cpu_acquire, rq, cpu, NULL); rq->scx.cpu_released = false; } if (prev->sched_class == &ext_sched_class) { update_curr_scx(rq); /* * If @prev is runnable & has slice left, it has priority and * fetching more just increases latency for the fetched tasks. * Tell pick_task_scx() to keep running @prev. If the BPF * scheduler wants to handle this explicitly, it should * implement ->cpu_release(). * * See scx_disable_workfn() for the explanation on the bypassing * test. */ if ((prev->scx.flags & SCX_TASK_QUEUED) && prev->scx.slice && !scx_bypassing(sch, cpu)) { verdict = SCX_DSP_PREV; goto has_tasks; } } /* if there already are tasks to run, nothing to do */ if (rq->scx.local_dsq.nr) { verdict = SCX_DSP_LOCAL; goto has_tasks; } verdict = scx_dispatch_sched(sch, rq, prev, false); if (verdict != SCX_DSP_NONE) goto has_tasks; /* * Didn't find another task to run. Keep running @prev unless * %SCX_OPS_ENQ_LAST is in effect. */ if ((prev->scx.flags & SCX_TASK_QUEUED) && (!(sch->ops.flags & SCX_OPS_ENQ_LAST) || scx_bypassing(sch, cpu)) && scx_task_can_stay_on_cpu(rq, prev)) { __scx_add_event(sch, SCX_EV_DISPATCH_KEEP_LAST, 1); verdict = SCX_DSP_PREV; goto has_tasks; } rq->scx.flags &= ~SCX_RQ_IN_DISPATCH; return SCX_DSP_NONE; has_tasks: /* * @rq may have extra IMMED tasks without reenq scheduled: * * - rq_is_open() can't reliably tell when and how slice is going to be * modified for $curr and allows IMMED tasks to be queued while * dispatch is in progress. * * - A non-IMMED HEAD task can get queued in front of an IMMED task * between the IMMED queueing and the subsequent scheduling event. */ if (unlikely(rq->scx.local_dsq.nr > 1 && rq->scx.nr_immed)) scx_schedule_reenq_local(rq, 0); rq->scx.flags &= ~SCX_RQ_IN_DISPATCH; return verdict; } static void set_next_task_scx(struct rq *rq, struct task_struct *p, bool first) { struct scx_sched *sch = scx_task_sched(p); if (p->scx.flags & SCX_TASK_QUEUED) { /* * Core-sched might decide to execute @p before it is * dispatched. Call ops_dequeue() to notify the BPF scheduler. */ ops_dequeue(rq, p, SCX_DEQ_CORE_SCHED_EXEC); scx_dispatch_dequeue(rq, p); } p->se.exec_start = rq_clock_task(rq); /* see dequeue_task_scx() on why we skip when !QUEUED */ if (SCX_HAS_OP(sch, running) && (p->scx.flags & SCX_TASK_QUEUED)) SCX_CALL_OP_TASK(sch, running, rq, p); clr_task_runnable(p, true); /* apply any pending out-of-band slice request before the tick decision */ apply_task_slice_oob(rq, p); /* * @p is getting newly scheduled or got kicked after someone updated its * slice. Update SCX_RQ_CAN_STOP_TICK to reflect whether the tick can be * stopped. See scx_can_stop_tick(). * * Moreover, refresh the load_avgs just when transitioning in and out of * nohz. In the future, we might want to add a mechanism to update * load_avgs periodically on tick-stopped CPUs. */ if (p->scx.slice == SCX_SLICE_INF) { if (!(rq->scx.flags & SCX_RQ_CAN_STOP_TICK)) { /* * Bypass mode always assigns finite slices, so @p * can't have an infinite slice while bypassing. * Therefore, sched_update_tick_dependency() can safely * evaluate the outgoing task. */ rq->scx.flags |= SCX_RQ_CAN_STOP_TICK; sched_update_tick_dependency(rq); update_other_load_avgs(rq); } } else { if (rq->scx.flags & SCX_RQ_CAN_STOP_TICK) { rq->scx.flags &= ~SCX_RQ_CAN_STOP_TICK; update_other_load_avgs(rq); } /* * @rq still references the outgoing scheduling context. A finite * slice is sufficient by itself to require the tick. */ if (tick_nohz_full_cpu(cpu_of(rq))) tick_nohz_dep_set_cpu(cpu_of(rq), TICK_DEP_BIT_SCHED); } } static enum scx_cpu_preempt_reason preempt_reason_from_class(const struct sched_class *class) { if (class == &stop_sched_class) return SCX_CPU_PREEMPT_STOP; if (class == &dl_sched_class) return SCX_CPU_PREEMPT_DL; if (class == &rt_sched_class) return SCX_CPU_PREEMPT_RT; return SCX_CPU_PREEMPT_UNKNOWN; } static void switch_class(struct rq *rq, struct task_struct *next) { struct scx_sched *sch = scx_root_protected_live(); const struct sched_class *next_class = next->sched_class; if (!(sch->ops.flags & SCX_OPS_HAS_CPU_PREEMPT)) return; /* * The callback is conceptually meant to convey that the CPU is no * longer under the control of SCX. Therefore, don't invoke the callback * if the next class is below SCX (in which case the BPF scheduler has * actively decided not to schedule any tasks on the CPU). */ if (sched_class_above(&ext_sched_class, next_class)) return; /* * At this point we know that SCX was preempted by a higher priority * sched_class, so invoke the ->cpu_release() callback if we have not * done so already. We only send the callback once between SCX being * preempted, and it regaining control of the CPU. * * ->cpu_release() complements ->cpu_acquire(), which is emitted the * next time that dispatch_one() is invoked. */ if (!rq->scx.cpu_released) { if (sch->ops.cpu_release) { struct scx_cpu_release_args args = { .reason = preempt_reason_from_class(next_class), .task = next, }; SCX_CALL_OP(sch, cpu_release, rq, cpu_of(rq), &args); } rq->scx.cpu_released = true; } } static void put_prev_task_scx(struct rq *rq, struct task_struct *p, struct task_struct *next) { struct scx_sched *sch = scx_task_sched(p); bool rescue_keep = false; /* see kick_sync_wait_bal_cb() */ smp_store_release(&rq->scx.kick_sync, rq->scx.kick_sync + 1); update_curr_scx(rq); /* * If the slice is consumed, protection ends with it. A rescuee * preempted beforehand keeps going, see scx_rescue_keep(). */ if (!p->scx.slice) { if (unlikely(p == scx_rescuee(rq))) rescue_keep = scx_rescue_keep(rq, p); if (!rescue_keep) scx_task_slice_ended(rq, p); } /* see dequeue_task_scx() on why we skip when !QUEUED */ if (SCX_HAS_OP(sch, stopping) && (p->scx.flags & SCX_TASK_QUEUED)) SCX_CALL_OP_TASK(sch, stopping, rq, p, true); if (p->scx.flags & SCX_TASK_QUEUED) { set_task_runnable(rq, p); /* * If @p has slice left and is being put, @p is getting * preempted by a higher priority scheduler class or core-sched * forcing a different task. Leave it at the head of the local * DSQ unless it was an IMMED task. IMMED tasks should not * linger on a busy CPU, reenqueue them to the BPF scheduler. * * An open rescue must keep @p on the local DSQ even if the * scheduler zeroed the slice in ops.stopping() above. */ if ((p->scx.slice || unlikely(p == scx_rescuee(rq))) && !scx_bypassing(sch, cpu_of(rq))) { if (p->scx.flags & SCX_TASK_IMMED) { p->scx.flags |= SCX_TASK_REENQ_PREEMPTED; scx_do_enqueue_task(rq, p, SCX_ENQ_REENQ, -1); p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK; } else { u64 enq_flags = 0; /* * Keep a preempted rescue going. If preempted * by another SCX task, append to the local DSQ, * see scx_rescue_keep(). */ if (unlikely(p == scx_rescuee(rq))) { enq_flags |= SCX_ENQ_IGNORE_CAPS; if (!rescue_keep) enq_flags |= SCX_ENQ_HEAD; } else { enq_flags |= SCX_ENQ_HEAD; } scx_dispatch_enqueue(sch, rq, &rq->scx.local_dsq, p, 0, 0, enq_flags); } goto switch_class; } /* * If @p is runnable but we're about to enter a lower * sched_class, %SCX_OPS_ENQ_LAST must be set. Tell * ops.enqueue() that @p is the only one available for this cpu, * which should trigger an explicit follow-up scheduling event. * This doesn't apply if the baseline access on the CPU is lost. * * Under core scheduling, a pick dispatches only when nothing is * locally runnable and can legitimately go idle with @p still * runnable (see do_pick_task_scx()). */ if (next && sched_class_above(&ext_sched_class, next->sched_class) && scx_task_can_stay_on_cpu(rq, p)) { WARN_ON_ONCE(!sched_core_enabled(rq) && !(sch->ops.flags & SCX_OPS_ENQ_LAST)); scx_do_enqueue_task(rq, p, SCX_ENQ_LAST, -1); } else { scx_do_enqueue_task(rq, p, 0, -1); } } switch_class: if (next && next->sched_class != &ext_sched_class) switch_class(rq, next); } static void kick_sync_wait_bal_cb(struct rq *rq) { struct scx_kick_syncs __rcu *ks; unsigned long *ksyncs; bool waited; s32 cpu; /* * This callback is queued and normally flushed within @rq's own * scheduling pass. However, dispatch can drop the rq lock while it sits * queued, and lock takers in that window (the sched class change paths, * the scx task iterator) flush pending balance callbacks on release, * running this one on a foreign CPU whose snapshots are unrelated. The * kicked CPUs are already on their way to advance the kick_syncs being * waited on. Don't get in the way. */ if (unlikely(cpu_of(rq) != smp_processor_id())) return; ks = __this_cpu_read(scx_kick_syncs); ksyncs = rcu_dereference_sched(ks)->syncs; /* * Drop rq lock and enable IRQs while waiting. IRQs must be enabled * — a target CPU may be waiting for us to process an IPI (e.g. TLB * flush) while we wait for its kick_sync to advance. * * Also, keep advancing our own kick_sync so that new kick_sync waits * targeting us, which can start after we drop the lock, cannot form * cyclic dependencies. */ retry: waited = false; for_each_cpu(cpu, rq->scx.cpus_to_sync) { /* * smp_load_acquire() pairs with smp_store_release() on * kick_sync updates on the target CPUs. */ if (cpu == cpu_of(rq) || smp_load_acquire(&cpu_rq(cpu)->scx.kick_sync) != ksyncs[cpu]) { cpumask_clear_cpu(cpu, rq->scx.cpus_to_sync); continue; } scx_rq_lock_drop(rq); raw_spin_rq_unlock_irq(rq); while (READ_ONCE(cpu_rq(cpu)->scx.kick_sync) == ksyncs[cpu]) { smp_store_release(&rq->scx.kick_sync, rq->scx.kick_sync + 1); cpu_relax(); } raw_spin_rq_lock_irq(rq); waited = true; } if (waited) goto retry; } static struct task_struct *first_local_task(struct rq *rq) { return list_first_entry_or_null(&rq->scx.local_dsq.list, struct task_struct, scx.dsq_list.node); } /* * Run dispatch and queue the follow-up work for a pick. */ static enum scx_dsp_verdict dispatch_pick(struct rq *rq, struct rq_flags *rf, struct task_struct *prev) { enum scx_dsp_verdict verdict; rq_unpin_lock(rq, rf); verdict = dispatch_one(rq, prev); rq_repin_lock(rq, rf); maybe_queue_balance_callback(rq); /* * Defer to a balance callback which can drop rq lock and enable IRQs. * Waiting directly in the pick path would deadlock against CPUs sending * us IPIs (e.g. TLB flushes) while we wait for them. */ if (unlikely(rq->scx.kick_sync_pending)) { rq->scx.kick_sync_pending = false; queue_balance_callback(rq, &rq->scx.kick_sync_bal_cb, kick_sync_wait_bal_cb); } return verdict; } #ifdef CONFIG_SCHED_CORE /* * Dispatch for a pick when core scheduling is enabled. The selection picks for * all SMT siblings and the rq_i->core_pick state it builds must stay atomic * throughout. If the dispatch released the rq lock, anything can have happened * in between - return %SCX_DSP_RETRY to restart the selection against current * state. */ static enum scx_dsp_verdict dispatch_core_pick(struct rq *rq, struct rq_flags *rf, struct task_struct *prev) { enum scx_dsp_verdict verdict; u32 seq = rq->scx.lock_drop_seq; /* another dispatch is in flight on @rq, let that handle it */ if (rq->scx.flags & SCX_RQ_IN_DISPATCH) return SCX_DSP_NONE; rq_unpin_lock(rq, rf); verdict = dispatch_one(rq, prev); if (cpu_of(rq) == smp_processor_id()) { maybe_queue_balance_callback(rq); /* see dispatch_pick() */ if (unlikely(rq->scx.kick_sync_pending)) { rq->scx.kick_sync_pending = false; queue_balance_callback(rq, &rq->scx.kick_sync_bal_cb, kick_sync_wait_bal_cb); } } else if (unlikely(rq->scx.flags & SCX_RQ_BAL_CB_PENDING)) { /* * Balance callbacks must run in the context that queued them, * so they can't be queued on another CPU's rq. Run the deferred * work directly instead. */ rq->scx.flags &= ~SCX_RQ_BAL_CB_PENDING; run_deferred(rq); } rq_repin_lock(rq, rf); /* if dispatch_one() released the rq lock, restart the selection */ if (rq->scx.lock_drop_seq != seq) return SCX_DSP_RETRY; return verdict; } #else /* CONFIG_SCHED_CORE */ static enum scx_dsp_verdict dispatch_core_pick(struct rq *rq, struct rq_flags *rf, struct task_struct *prev) { return SCX_DSP_NONE; } #endif /* CONFIG_SCHED_CORE */ static struct task_struct * do_pick_task_scx(struct rq *rq, struct rq_flags *rf, bool force_scx) { struct task_struct *prev = rq->curr; enum scx_dsp_verdict verdict; struct task_struct *p; /* see kick_sync_wait_bal_cb() */ smp_store_release(&rq->scx.kick_sync, rq->scx.kick_sync + 1); rq_modified_begin(rq, &ext_sched_class); if (sched_core_enabled(rq)) verdict = dispatch_core_pick(rq, rf, prev); else verdict = dispatch_pick(rq, rf, prev); if (verdict == SCX_DSP_RETRY) return RETRY_TASK; /* * If any higher-priority sched class enqueued a runnable task on this * rq during dispatch_one(), abort and return RETRY_TASK, so that the * scheduler loop can restart. * * If @force_scx is true, always try to pick a SCHED_EXT task, * regardless of any higher-priority sched classes activity. */ if (!force_scx && rq_modified_above(rq, &ext_sched_class)) return RETRY_TASK; /* * If we're keeping @prev, replenish slice if necessary and keep running * @prev. Otherwise, pop the first one from the local DSQ. */ if (verdict == SCX_DSP_PREV) { p = prev; if (!p->scx.slice) { /* the slice is consumed, protection ends */ scx_task_slice_ended(rq, p); refill_task_slice_dfl(scx_task_sched(p), p); } } else { p = first_local_task(rq); if (!p) return NULL; if (unlikely(!p->scx.slice) && scx_task_can_stay_on_cpu(rq, p)) { struct scx_sched *sch = scx_task_sched(p); if (!scx_bypassing(sch, cpu_of(rq)) && !sch->warned_zero_slice) { printk_deferred(KERN_WARNING "sched_ext: %s[%d] has zero slice in %s()\n", p->comm, p->pid, __func__); sch->warned_zero_slice = true; } refill_task_slice_dfl(sch, p); } } return p; } static struct task_struct *pick_task_scx(struct rq *rq, struct rq_flags *rf) { return do_pick_task_scx(rq, rf, false); } /* * Select the next task to run from the ext scheduling class. * * Use do_pick_task_scx() directly with @force_scx enabled, since the * dl_server must always select a sched_ext task. */ static struct task_struct * ext_server_pick_task(struct sched_dl_entity *dl_se, struct rq_flags *rf) { if (!scx_enabled()) return NULL; return do_pick_task_scx(dl_se->rq, rf, true); } /* * Initialize the ext server deadline entity. */ void ext_server_init(struct rq *rq) { struct sched_dl_entity *dl_se = &rq->ext_server; init_dl_entity(dl_se); dl_server_init(dl_se, rq, ext_server_pick_task); } #ifdef CONFIG_SCHED_CORE /** * scx_prio_less - Task ordering for core-sched * @a: task A * @b: task B * @in_fi: in forced idle state * * Core-sched is implemented as an additional scheduling layer on top of the * usual sched_class'es and needs to find out the expected task ordering. For * SCX, core-sched calls this function to interrogate the task ordering. * * A pair of tasks owned by one scheduler is ordered by the owner's * ops.core_sched_before(). A pair spanning two schedulers is ordered by their * nearest common ancestor which implements the op - the one case where the op * is called on tasks that the scheduler delegated to its sub-schedulers and may * not be scheduling anymore. * * When neither applies, or the deciding scheduler is bypassing on either task's * CPU, the default ordering runs the task which has been waiting longer first. * A running task counts as the most recently serviced and orders after every * waiting task. Waiting tasks are compared by @p->scx.runnable_at. * * Return: %true if @a should run after @b. */ bool scx_prio_less(const struct task_struct *a, const struct task_struct *b, bool in_fi) { struct scx_sched *sch_a = scx_task_sched(a); struct scx_sched *sch_b = scx_task_sched(b); struct scx_sched *sch = NULL; bool a_running, b_running; if (sch_a == sch_b) { if (SCX_HAS_OP(sch_a, core_sched_before)) sch = sch_a; } else { s32 level; for (level = min(sch_a->level, sch_b->level); level >= 0; level--) { struct scx_sched *anc = sch_a->ancestors[level]; if (anc == sch_b->ancestors[level] && SCX_HAS_OP(anc, core_sched_before)) { sch = anc; break; } } } /* * scx_prio_less() returns whether @a should run after @b while * ops.core_sched_before() returns whether its first argument should run * before the second. Swap the arguments. * * The const qualifiers are dropped from task_struct pointers when * calling ops.core_sched_before(). Accesses are controlled by the * verifier. */ if (sch && !scx_bypassing(sch, task_cpu(a)) && !scx_bypassing(sch, task_cpu(b))) return SCX_CALL_OP_2TASKS_RET(sch, core_sched_before, task_rq(a), (struct task_struct *)b, (struct task_struct *)a); /* * runnable_at is refreshed only on enqueue, so a task which keeps * occupying its CPU carries a stale stamp. A running task is the most * recently serviced whatever its stamp says. Order it after every * waiting task. */ a_running = a->on_cpu; b_running = b->on_cpu; if (a_running != b_running) return a_running; return time_after(a->scx.runnable_at, b->scx.runnable_at); } #endif /* CONFIG_SCHED_CORE */ static int select_task_rq_scx(struct task_struct *p, int prev_cpu, int wake_flags) { struct scx_sched *sch = scx_task_sched(p); bool bypassing; /* * sched_exec() calls with %WF_EXEC when @p is about to exec(2) as it * can be a good migration opportunity with low cache and memory * footprint. Returning a CPU different than @prev_cpu triggers * immediate rq migration. However, for SCX, as the current rq * association doesn't dictate where the task is going to run, this * doesn't fit well. If necessary, we can later add a dedicated method * which can decide to preempt self to force it through the regular * scheduling path. */ if (unlikely(wake_flags & WF_EXEC)) return prev_cpu; bypassing = scx_bypassing(sch, task_cpu(p)); if (likely(SCX_HAS_OP(sch, select_cpu)) && !bypassing) { s32 cpu; struct task_struct **ddsp_taskp; ddsp_taskp = this_cpu_ptr(&direct_dispatch_task); WARN_ON_ONCE(*ddsp_taskp); *ddsp_taskp = p; this_rq()->scx.in_select_cpu = true; cpu = SCX_CALL_OP_TASK_RET(sch, select_cpu, NULL, p, scx_cpu_arg(prev_cpu), wake_flags); cpu = scx_cpu_ret(sch, cpu); this_rq()->scx.in_select_cpu = false; p->scx.selected_cpu = cpu; *ddsp_taskp = NULL; if (scx_cpu_valid(sch, cpu, "from ops.select_cpu()")) return cpu; else return prev_cpu; } else { s32 cpu; /* * While bypassing, the enqueue path routes @p to a bypass DSQ * without consulting the direct-dispatch target, making the * default selection pointless. It doesn't work anyway when the * scheduler does its own idle tracking and the built-in idle * cpumasks are not updated. Leave @p on @prev_cpu. */ if (bypassing) { __scx_add_event(sch, SCX_EV_BYPASS_DISPATCH, 1); p->scx.selected_cpu = prev_cpu; return prev_cpu; } cpu = scx_select_cpu_dfl(p, prev_cpu, wake_flags, NULL, 0); if (cpu >= 0) { /* * Carry the slice refill and let the insertion commit * it under rq lock. See the write rules. */ __scx_add_event(sch, SCX_EV_REFILL_SLICE_DFL, 1); p->scx.ddsp_slice = READ_ONCE(sch->slice_dfl); p->scx.ddsp_enq_flags = SCX_ENQ_SLICE_DFL; p->scx.ddsp_dsq_id = SCX_DSQ_LOCAL; } else { cpu = prev_cpu; } p->scx.selected_cpu = cpu; return cpu; } } static void task_woken_scx(struct rq *rq, struct task_struct *p) { run_deferred(rq); } static void set_cpus_allowed_scx(struct task_struct *p, struct affinity_context *ac) { struct scx_sched *sch = scx_task_sched(p); set_cpus_allowed_common(p, ac); if (task_dead_and_done(p)) return; /* * The effective cpumask is stored in @p->cpus_ptr which may temporarily * differ from the configured one in @p->cpus_mask. Always tell the bpf * scheduler the effective one. * * Fine-grained memory write control is enforced by BPF making the const * designation pointless. Cast it away when calling the operation. */ if (SCX_HAS_OP(sch, set_cpumask)) scx_call_op_set_cpumask(sch, task_rq(p), p, (struct cpumask *)p->cpus_ptr); } static void handle_hotplug(struct rq *rq, bool online) { struct scx_sched *sch = scx_root_protected(); s32 cpu = cpu_of(rq); s32 cpu_or_cid = cpu; atomic_long_inc(&scx_hotplug_seq); /* * scx_root updates are protected by cpus_read_lock() and will stay * stable here. Note that we can't depend on scx_enabled() test as the * hotplug ops need to be enabled before __scx_enabled is set. */ if (unlikely(!sch)) return; if (scx_enabled()) scx_idle_update_selcpu_topology(&sch->ops); if (online) scx_online_ecaps(rq); else scx_offline_ecaps(rq); /* * The tables can't be retired while this function is running as the * retirement is inside cpus_read_lock. However, scx_cpu_arg() is * awkward here as the tables can be NULL after root enable failure and * lockdep would trigger without surrounding rcu_read_lock(). Open code * the translation. If the table is NULL, the ops are also cleared and * @cpu_or_cid goes unused. */ if (scx_is_cid_type()) { s16 *tbl = rcu_dereference_check(scx_cpu_to_cid_tbl, lockdep_is_cpus_held()); if (tbl) cpu_or_cid = tbl[cpu]; } if (online && SCX_HAS_OP(sch, cpu_online)) SCX_CALL_OP(sch, cpu_online, NULL, cpu_or_cid); else if (!online && SCX_HAS_OP(sch, cpu_offline)) SCX_CALL_OP(sch, cpu_offline, NULL, cpu_or_cid); else scx_exit(sch, SCX_EXIT_UNREG_KERN, SCX_ECODE_ACT_RESTART | SCX_ECODE_RSN_HOTPLUG, "cpu %d going %s, exiting scheduler", cpu, online ? "online" : "offline"); } void scx_rq_activate(struct rq *rq) { handle_hotplug(rq, true); } void scx_rq_deactivate(struct rq *rq) { handle_hotplug(rq, false); } static void rq_online_scx(struct rq *rq) { rq->scx.flags |= SCX_RQ_ONLINE; } static void rq_offline_scx(struct rq *rq) { rq->scx.flags &= ~SCX_RQ_ONLINE; scx_rescue_flush(rq); } static bool check_rq_for_timeouts(struct rq *rq) { struct scx_sched *sch; struct task_struct *p; struct rq_flags rf; bool timed_out = false; rq_lock_irqsave(rq, &rf); sch = rcu_dereference_bh(scx_root); if (unlikely(!sch)) goto out_unlock; list_for_each_entry(p, &rq->scx.runnable_list, scx.runnable_node) { struct scx_sched *sch = scx_task_sched(p); unsigned long last_runnable = p->scx.runnable_at; if (unlikely(time_after(jiffies, last_runnable + READ_ONCE(sch->watchdog_timeout)))) { struct scx_dispatch_q *dsq = READ_ONCE(p->scx.dsq); u32 dur_ms = jiffies_to_msecs(jiffies - last_runnable); /* * A task can be stuck on a DSQ that a sched other than * its owner is responsible for draining, e.g. an * ancestor's bypass DSQ while the owner is bypassing. * Blame the drainer. The local DSQ is consumed by the * cpu itself and keeps blame on the owner. */ if (dsq && dsq->sched && dsq->id != SCX_DSQ_LOCAL) sch = dsq->sched; __scx_exit(sch, SCX_EXIT_ERROR_STALL, 0, cpu_of(rq), "%s[%d] failed to run for %u.%03us", p->comm, p->pid, dur_ms / 1000, dur_ms % 1000); timed_out = true; break; } } out_unlock: rq_unlock_irqrestore(rq, &rf); return timed_out; } static void scx_watchdog_workfn(struct work_struct *work) { unsigned long intv; int cpu; WRITE_ONCE(scx_watchdog_timestamp, jiffies); for_each_online_cpu(cpu) { if (unlikely(check_rq_for_timeouts(cpu_rq(cpu)))) break; cond_resched(); } intv = READ_ONCE(scx_watchdog_interval); if (intv < ULONG_MAX) queue_delayed_work(system_dfl_wq, to_delayed_work(work), intv); } void scx_tick(struct rq *rq) { struct scx_sched *root; unsigned long last_check; if (!scx_enabled()) return; root = rcu_dereference_bh(scx_root); if (unlikely(!root)) return; last_check = READ_ONCE(scx_watchdog_timestamp); if (unlikely(time_after(jiffies, last_check + READ_ONCE(root->watchdog_timeout)))) { u32 dur_ms = jiffies_to_msecs(jiffies - last_check); scx_exit(root, SCX_EXIT_ERROR_STALL, 0, "watchdog failed to check in for %u.%03us", dur_ms / 1000, dur_ms % 1000); } update_other_load_avgs(rq); } static void task_tick_scx(struct rq *rq, struct task_struct *curr, int queued) { struct scx_sched *sch = scx_task_sched(curr); update_curr_scx(rq); /* * While disabling, always resched as we can't trust the slice * management. */ if (scx_bypassing(sch, cpu_of(rq))) scx_set_task_slice(curr, 0); else if (SCX_HAS_OP(sch, tick)) SCX_CALL_OP_TASK(sch, tick, rq, curr); if (!curr->scx.slice) resched_curr(rq); } #ifdef CONFIG_EXT_GROUP_SCHED static struct cgroup *tg_cgrp(struct task_group *tg) { /* * If CGROUP_SCHED is disabled, @tg is NULL. If @tg is an autogroup, * @tg->css.cgroup is NULL. In both cases, @tg can be treated as the * root cgroup. */ if (tg && tg->css.cgroup) return tg->css.cgroup; else return &cgrp_dfl_root.cgrp; } #define SCX_INIT_TASK_ARGS_CGROUP(cgrp) .cgroup = (cgrp), #else /* CONFIG_EXT_GROUP_SCHED */ #define SCX_INIT_TASK_ARGS_CGROUP(cgrp) #endif /* CONFIG_EXT_GROUP_SCHED */ /** * __scx_init_task - Initialize a task for a sched * @sch: sched to initialize @p for * @p: task of interest * @cgrp: cgroup @p is joining, %NULL for @p's current task_group's cgroup * @fork: %true if @p is being forked * * Pre-commit cgroup migration passes @cgrp explicitly as @p's task_group * still reflects the source. * * Return 0 on success, -errno on failure. */ int __scx_init_task(struct scx_sched *sch, struct task_struct *p, struct cgroup *cgrp, bool fork) { int ret; p->scx.disallow = false; if (SCX_HAS_OP(sch, init_task)) { struct scx_init_task_args args = { SCX_INIT_TASK_ARGS_CGROUP(cgrp ?: tg_cgrp(task_group(p))) .fork = fork, }; ret = SCX_CALL_OP_RET(sch, init_task, NULL, p, &args); if (unlikely(ret)) { ret = scx_ops_sanitize_err(sch, "init_task", ret); return ret; } } if (p->scx.disallow) { if (unlikely(scx_parent(sch))) { scx_error(sch, "non-root ops.init_task() set task->scx.disallow for %s[%d]", p->comm, p->pid); } else if (unlikely(fork)) { scx_error(sch, "ops.init_task() set task->scx.disallow for %s[%d] during fork", p->comm, p->pid); } else if (unlikely(scx_enable_state() != SCX_ENABLING)) { scx_error(sch, "ops.init_task() set task->scx.disallow for %s[%d] outside the enable path", p->comm, p->pid); } else { struct rq *rq; struct rq_flags rf; rq = task_rq_lock(p, &rf); /* * We're in the load path and @p->policy will be applied * right after. Reverting @p->policy here and rejecting * %SCHED_EXT transitions from scx_check_setscheduler() * guarantees that if ops.init_task() sets @p->disallow, * @p can never be in SCX. */ if (p->policy == SCHED_EXT) { p->policy = SCHED_NORMAL; atomic_long_inc(&scx_nr_rejected); } task_rq_unlock(rq, p, &rf); } } return 0; } static void __scx_enable_task(struct scx_sched *sch, struct task_struct *p) { struct rq *rq = task_rq(p); u32 weight; lockdep_assert_rq_held(rq); /* * Verify the task is not in BPF scheduler's custody. If flag * transitions are consistent, the flag should always be clear * here. */ WARN_ON_ONCE(p->scx.flags & SCX_TASK_IN_CUSTODY); /* * Set the weight before calling ops.enable() so that the scheduler * doesn't see a stale value if they inspect the task struct. */ if (task_has_idle_policy(p)) weight = WEIGHT_IDLEPRIO; else weight = sched_prio_to_weight[p->static_prio - MAX_RT_PRIO]; p->scx.weight = sched_weight_to_cgroup(weight); if (SCX_HAS_OP(sch, enable)) SCX_CALL_OP_TASK(sch, enable, rq, p); if (SCX_HAS_OP(sch, set_weight)) SCX_CALL_OP_TASK(sch, set_weight, rq, p, p->scx.weight); } void scx_enable_task(struct scx_sched *sch, struct task_struct *p) { __scx_enable_task(sch, p); scx_set_task_state(p, SCX_TASK_ENABLED); } static void scx_disable_task(struct scx_sched *sch, struct task_struct *p) { struct rq *rq = task_rq(p); lockdep_assert_rq_held(rq); WARN_ON_ONCE(scx_get_task_state(p) != SCX_TASK_ENABLED); clear_direct_dispatch(p); if (SCX_HAS_OP(sch, disable)) SCX_CALL_OP_TASK(sch, disable, rq, p); scx_set_task_state(p, SCX_TASK_READY); /* * Reset the SCX-managed fields when @p leaves the BPF scheduler's * control, after ops.disable() has observed their final values. */ p->scx.dsq_vtime = 0; scx_task_slice_ended(rq, p); scx_set_task_slice(p, 0); p->scx.reenq_cnt = 0; /* * Verify the task is not in BPF scheduler's custody. If flag * transitions are consistent, the flag should always be clear * here. */ WARN_ON_ONCE(p->scx.flags & SCX_TASK_IN_CUSTODY); } void __scx_disable_and_exit_task(struct scx_sched *sch, struct task_struct *p) { struct scx_exit_task_args args = { .cancelled = false, }; lockdep_assert_held(&p->pi_lock); lockdep_assert_rq_held(task_rq(p)); switch (scx_get_task_state(p)) { case SCX_TASK_NONE: return; case SCX_TASK_INIT: args.cancelled = true; break; case SCX_TASK_READY: break; case SCX_TASK_ENABLED: scx_disable_task(sch, p); break; default: WARN_ON_ONCE(true); return; } if (SCX_HAS_OP(sch, exit_task)) SCX_CALL_OP_TASK(sch, exit_task, task_rq(p), p, &args); } /* * Undo a completed __scx_init_task(sch, p, false) when scx_enable_task() never * ran. The task state has not been transitioned, so this mirrors the * SCX_TASK_INIT branch in __scx_disable_and_exit_task(). */ void scx_sub_init_cancel_task(struct scx_sched *sch, struct task_struct *p) { struct scx_exit_task_args args = { .cancelled = true }; lockdep_assert_held(&p->pi_lock); lockdep_assert_rq_held(task_rq(p)); /* @p was never associated with @sch, dispatch on the explicit @sch */ if (SCX_HAS_OP(sch, exit_task)) __SCX_CALL_OP_TASK(sch, ops, exit_task, task_rq(p), p, &args); } void scx_disable_and_exit_task(struct scx_sched *sch, struct task_struct *p) { __scx_disable_and_exit_task(sch, p); /* * If set, @p exited between __scx_init_task() and scx_enable_task() in * scx_sub_enable() and is initialized for both the associated sched and * its parent. Exit for the child too - scx_enable_task() never ran for * it, so undo only init_task. The flag is only set on the sub-enable * path, so it's always clear when @p arrives here in %SCX_TASK_NONE. */ if (p->scx.flags & SCX_TASK_SUB_INIT) { if (!WARN_ON_ONCE(!scx_enabling_sub_sched)) scx_sub_init_cancel_task(scx_enabling_sub_sched, p); p->scx.flags &= ~SCX_TASK_SUB_INIT; } scx_set_task_sched(p, NULL); scx_set_task_state(p, SCX_TASK_NONE); } void init_scx_entity(struct sched_ext_entity *scx) { memset(scx, 0, sizeof(*scx)); INIT_LIST_HEAD(&scx->dsq_list.node); RB_CLEAR_NODE(&scx->dsq_priq); scx->sticky_cpu = -1; scx->holding_cpu = -1; scx->runnable_cpu = -1; INIT_LIST_HEAD(&scx->runnable_node); scx->runnable_at = jiffies; scx->ddsp_dsq_id = SCX_DSQ_INVALID; scx->slice = SCX_SLICE_DFL; } /* See scx_tid_alloc / scx_tid_cursor. */ static u64 scx_alloc_tid(void) { struct scx_tid_alloc *ta; guard(preempt)(); ta = this_cpu_ptr(&scx_tid_alloc); if (unlikely(ta->next >= ta->end)) { ta->next = atomic64_fetch_add(SCX_TID_CHUNK, &scx_tid_cursor); ta->end = ta->next + SCX_TID_CHUNK; } return ta->next++; } static void scx_tid_hash_insert(struct task_struct *p) { int ret; lockdep_assert_held(&scx_tasks_lock); ret = rhashtable_lookup_insert_fast(&scx_tid_hash, &p->scx.tid_hash_node, scx_tid_hash_params); WARN_ON_ONCE(ret); } void scx_pre_fork(struct task_struct *p) { /* * BPF scheduler enable/disable paths want to be able to iterate and * update all tasks which can become complex when racing forks. As * enable/disable are very cold paths, let's use a percpu_rwsem to * exclude forks. */ percpu_down_read(&scx_fork_rwsem); } int scx_fork(struct task_struct *p, struct kernel_clone_args *kargs) { s32 ret; percpu_rwsem_assert_held(&scx_fork_rwsem); p->scx.tid = scx_alloc_tid(); if (scx_init_task_enabled) { #ifdef CONFIG_EXT_SUB_SCHED struct scx_sched *sch = scx_cgroup_sched(kargs->cset->dfl_cgrp); #else struct scx_sched *sch = scx_root_protected_live(); #endif scx_set_task_state(p, SCX_TASK_INIT_BEGIN); ret = __scx_init_task(sch, p, NULL, true); if (unlikely(ret)) { scx_set_task_state(p, SCX_TASK_NONE); return ret; } scx_set_task_state(p, SCX_TASK_INIT); scx_set_task_sched(p, sch); } return 0; } void scx_post_fork(struct task_struct *p) { if (scx_init_task_enabled) { scx_set_task_state(p, SCX_TASK_READY); /* * Enable the task immediately if it's running on sched_ext. * Otherwise, it'll be enabled in switching_to_scx() if and * when it's ever configured to run with a SCHED_EXT policy. */ if (p->sched_class == &ext_sched_class) { struct rq_flags rf; struct rq *rq; rq = task_rq_lock(p, &rf); scx_enable_task(scx_task_sched(p), p); task_rq_unlock(rq, p, &rf); } } scoped_guard(raw_spinlock_irq, &scx_tasks_lock) { list_add_tail(&p->scx.tasks_node, &scx_tasks); if (scx_tid_to_task_enabled()) scx_tid_hash_insert(p); } percpu_up_read(&scx_fork_rwsem); } void scx_cancel_fork(struct task_struct *p) { if (scx_init_task_enabled) { struct rq *rq; struct rq_flags rf; rq = task_rq_lock(p, &rf); WARN_ON_ONCE(scx_get_task_state(p) >= SCX_TASK_READY); scx_disable_and_exit_task(scx_task_sched(p), p); task_rq_unlock(rq, p, &rf); } percpu_up_read(&scx_fork_rwsem); } /** * task_dead_and_done - Is a task dead and done running? * @p: target task * * Once sched_ext_dead() removes the dead task from scx_tasks and exits it, the * task no longer exists from SCX's POV. However, certain sched_class ops may be * invoked on these dead tasks leading to failures - e.g. sched_setscheduler() * may try to switch a task which finished sched_ext_dead() back into SCX * triggering invalid SCX task state transitions and worse. * * Once a task has finished the final switch, sched_ext_dead() is the only thing * that needs to happen on the task. Use this test to short-circuit sched_class * operations which may be called on dead tasks. */ static bool task_dead_and_done(struct task_struct *p) { struct rq *rq = task_rq(p); lockdep_assert_rq_held(rq); /* * In do_task_dead(), a dying task sets %TASK_DEAD with preemption * disabled and __schedule(). If @p has %TASK_DEAD set and off CPU, @p * won't ever run again. */ return unlikely(READ_ONCE(p->__state) == TASK_DEAD) && !task_on_cpu(rq, p); } void sched_ext_dead(struct task_struct *p) { /* * By the time control reaches here, @p has %TASK_DEAD set, switched out * for the last time and then dropped the rq lock - task_dead_and_done() * should be returning %true nullifying the straggling sched_class ops. * Remove from scx_tasks and exit @p. */ scoped_guard(raw_spinlock_irqsave, &scx_tasks_lock) { list_del_init(&p->scx.tasks_node); if (scx_tid_to_task_enabled()) rhashtable_remove_fast(&scx_tid_hash, &p->scx.tid_hash_node, scx_tid_hash_params); } /* * @p is off scx_tasks and wholly ours. scx_root_enable()'s READY -> * ENABLED transitions can't race us. Disable ops for @p. * * %SCX_TASK_DEAD synchronizes against cgroup task iteration - see * scx_task_iter_next_locked(). NONE tasks need no marking: cgroup * iteration is only used from sub-sched paths, which require root * enabled. Root enable transitions every live task to at least READY. * * %INIT_BEGIN means ops.init_task() is running for @p. Don't call * into ops; transition to %DEAD so the post-init recheck unwinds * via scx_sub_init_cancel_task(). */ if (scx_get_task_state(p) != SCX_TASK_NONE) { struct rq_flags rf; struct rq *rq; rq = task_rq_lock(p, &rf); if (scx_get_task_state(p) != SCX_TASK_INIT_BEGIN) scx_disable_and_exit_task(scx_task_sched(p), p); scx_set_task_state(p, SCX_TASK_DEAD); task_rq_unlock(rq, p, &rf); } } static void reweight_task_scx(struct rq *rq, struct task_struct *p, const struct load_weight *lw) { struct scx_sched *sch = scx_task_sched(p); lockdep_assert_rq_held(task_rq(p)); if (task_dead_and_done(p)) return; /* * When switching sched_class away from SCX, reweight_task_scx() * is called _after_ scx_disable_task(). Skip calling ops.set_weight() * since the BPF scheduler may have already forgotten the task in * ops.disable(). * p->scx.weight will be recalculated in scx_enable_task() if the task * ever returns to SCX class. */ if (scx_get_task_state(p) != SCX_TASK_ENABLED) return; p->scx.weight = sched_weight_to_cgroup(scale_load_down(lw->weight)); if (SCX_HAS_OP(sch, set_weight)) SCX_CALL_OP_TASK(sch, set_weight, rq, p, p->scx.weight); } static void prio_changed_scx(struct rq *rq, struct task_struct *p, u64 oldprio) { } static void switching_to_scx(struct rq *rq, struct task_struct *p) { struct scx_sched *sch = scx_task_sched(p); if (task_dead_and_done(p)) return; scx_enable_task(sch, p); /* * set_cpus_allowed_scx() is not called while @p is associated with a * different scheduler class. Keep the BPF scheduler up-to-date. */ if (SCX_HAS_OP(sch, set_cpumask)) scx_call_op_set_cpumask(sch, rq, p, (struct cpumask *)p->cpus_ptr); } static void switched_from_scx(struct rq *rq, struct task_struct *p) { if (task_dead_and_done(p)) return; /* * %NONE means SCX is no longer tracking @p at the task level (e.g. * scx_fail_parent() handed @p back to the parent at NONE pending the * parent's own teardown). There is nothing to disable; calling * scx_disable_task() would WARN on the non-%ENABLED state and trigger a * NONE -> READY validation failure. */ if (scx_get_task_state(p) == SCX_TASK_NONE) return; scx_disable_task(scx_task_sched(p), p); } static void switched_to_scx(struct rq *rq, struct task_struct *p) {} int scx_check_setscheduler(struct task_struct *p, int policy) { lockdep_assert_rq_held(task_rq(p)); /* if disallow, reject transitioning into SCX */ if (scx_enabled() && READ_ONCE(p->scx.disallow) && p->policy != policy && policy == SCHED_EXT) return -EACCES; return 0; } static void process_ddsp_deferred_locals(struct rq *rq) { struct task_struct *p; lockdep_assert_rq_held(rq); /* * Now that @rq can be unlocked, execute the deferred enqueueing of * tasks directly dispatched to the local DSQs of other CPUs. See * direct_dispatch(). Keep popping from the head instead of using * list_for_each_entry_safe() as dispatch_local_dsq() may unlock @rq * temporarily. */ while ((p = list_first_entry_or_null(&rq->scx.ddsp_deferred_locals, struct task_struct, scx.dsq_list.node))) { struct scx_sched *sch = scx_task_sched(p); struct scx_dispatch_q *dsq; u64 dsq_id = p->scx.ddsp_dsq_id; u64 enq_flags = p->scx.ddsp_enq_flags; u64 slice = p->scx.ddsp_slice; u64 vtime = p->scx.ddsp_vtime; list_del_init(&p->scx.dsq_list.node); clear_direct_dispatch(p); dsq = find_dsq_for_dispatch(sch, rq, dsq_id, task_cpu(p)); if (!WARN_ON_ONCE(dsq->id != SCX_DSQ_LOCAL)) dispatch_to_local_dsq(sch, rq, dsq, p, slice, vtime, enq_flags); } } /* * Determine whether @p should be reenqueued from a local DSQ. * * @reenq_flags is mutable and accumulates state across the DSQ walk: * * - %SCX_REENQ_TSR_NOT_FIRST: Set after the first task is visited. "First" * tracks position in the DSQ list, not among IMMED tasks. A non-IMMED task at * the head consumes the first slot. * * - %SCX_REENQ_TSR_RQ_OPEN: Set by reenq_local() before the walk if * rq_is_open() is true. * * An IMMED task is kept (returns %false) only if it's the first task in the DSQ * AND the current task is done — i.e. it will execute immediately. All other * IMMED tasks are reenqueued. This means if a non-IMMED task sits at the head, * every IMMED task behind it gets reenqueued. * * Reenqueued tasks go through ops.enqueue() with %SCX_ENQ_REENQ | * %SCX_TASK_REENQ_IMMED. If the BPF scheduler dispatches back to the same local * DSQ with %SCX_ENQ_IMMED while the CPU is still unavailable, this triggers * another reenq cycle. Repetitions are bounded by %SCX_REENQ_MAX_REPEAT in * scx_do_enqueue_task(), which ejects the task's owning scheduler. */ static bool local_task_should_reenq(struct rq *rq, struct task_struct *p, u64 *reenq_flags, u32 *reason) { bool first; first = !(*reenq_flags & SCX_REENQ_TSR_NOT_FIRST); *reenq_flags |= SCX_REENQ_TSR_NOT_FIRST; if (unlikely((p->scx.flags & SCX_TASK_PROTECTED) || p == scx_rescuee(rq))) return false; *reason = SCX_TASK_REENQ_KFUNC; if ((p->scx.flags & SCX_TASK_IMMED) && (!first || !(*reenq_flags & SCX_REENQ_TSR_RQ_OPEN))) { __scx_add_event(scx_task_sched(p), SCX_EV_REENQ_IMMED, 1); *reason = SCX_TASK_REENQ_IMMED; return true; } if ((*reenq_flags & SCX_REENQ_CAP_REVOKE) && scx_task_reenq_on_cap_revoke(rq, p)) { *reason = SCX_TASK_REENQ_CAP; return true; } return *reenq_flags & SCX_REENQ_ANY; } static u32 reenq_local(struct scx_sched *sch, struct rq *rq, u64 reenq_flags) { LIST_HEAD(tasks); u32 nr_enqueued = 0; struct task_struct *p, *n; lockdep_assert_rq_held(rq); if (WARN_ON_ONCE(reenq_flags & __SCX_REENQ_TSR_MASK)) reenq_flags &= ~__SCX_REENQ_TSR_MASK; if (rq_is_open(rq, 0)) reenq_flags |= SCX_REENQ_TSR_RQ_OPEN; /* * The BPF scheduler may choose to dispatch tasks back to * @rq->scx.local_dsq. Move all candidate tasks off to a private list * first to avoid processing the same tasks repeatedly. */ list_for_each_entry_safe(p, n, &rq->scx.local_dsq.list, scx.dsq_list.node) { struct scx_sched *task_sch = scx_task_sched(p); u32 reason; /* * If @p is being migrated, @p's current CPU may not agree with * its allowed CPUs and the migration_cpu_stop is about to * deactivate and re-activate @p anyway. Skip re-enqueueing. * * While racing sched property changes may also dequeue and * re-enqueue a migrating task while its current CPU and allowed * CPUs disagree, they use %ENQUEUE_RESTORE which is bypassed to * the current local DSQ for running tasks and thus are not * visible to the BPF scheduler. */ if (p->migration_pending) continue; if (!scx_is_descendant(task_sch, sch)) continue; if (!local_task_should_reenq(rq, p, &reenq_flags, &reason)) continue; scx_dispatch_dequeue(rq, p); if (WARN_ON_ONCE(p->scx.flags & SCX_TASK_REENQ_REASON_MASK)) p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK; p->scx.flags |= reason; list_add_tail(&p->scx.dsq_list.node, &tasks); } list_for_each_entry_safe(p, n, &tasks, scx.dsq_list.node) { list_del_init(&p->scx.dsq_list.node); scx_do_enqueue_task(rq, p, SCX_ENQ_REENQ, -1); p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK; nr_enqueued++; } /* * The revoke that scheduled this scan may have raced the pick: curr * may be a now-capless task, either one that kept running or one * promoted off the local DSQ between the ecaps sync and this scan. * Zero the slice to evict it. The enqueue gate blocks new capless * inserts, so no later pick can slip through after the scan. */ if ((reenq_flags & SCX_REENQ_CAP_REVOKE) && rq->curr->sched_class == &ext_sched_class && scx_task_reenq_on_cap_revoke(rq, rq->curr)) { scx_set_task_slice(rq->curr, 0); resched_curr(rq); } return nr_enqueued; } static void process_deferred_reenq_locals(struct rq *rq) { lockdep_assert_rq_held(rq); /* * A task can be re-queued within this loop when a reenqueued task * bounces straight back to the local DSQ. That recursion is bounded by * the per-task reenqueue cap in scx_do_enqueue_task(). */ while (true) { struct scx_sched *sch; u64 reenq_flags; scoped_guard (raw_spinlock, &rq->scx.deferred_reenq_lock) { struct scx_deferred_reenq_local *drl = list_first_entry_or_null(&rq->scx.deferred_reenq_locals, struct scx_deferred_reenq_local, node); struct scx_sched_pcpu *sch_pcpu; if (!drl) return; sch_pcpu = container_of(drl, struct scx_sched_pcpu, deferred_reenq_local); sch = sch_pcpu->sch; reenq_flags = drl->flags; WRITE_ONCE(drl->flags, 0); list_del_init(&drl->node); } /* see schedule_dsq_reenq() */ smp_mb(); reenq_local(sch, rq, reenq_flags); } } static bool user_task_should_reenq(struct task_struct *p, u64 reenq_flags, u32 *reason) { *reason = SCX_TASK_REENQ_KFUNC; return reenq_flags & SCX_REENQ_ANY; } static void reenq_user(struct rq *rq, struct scx_dispatch_q *dsq, u64 reenq_flags) { struct rq *locked_rq = rq; struct scx_sched *sch = dsq->sched; struct scx_dsq_list_node cursor = INIT_DSQ_LIST_CURSOR(cursor, dsq, 0); struct task_struct *p; s32 nr_enqueued = 0; lockdep_assert_rq_held(rq); raw_spin_lock(&dsq->lock); while (likely(!READ_ONCE(sch->bypass_depth))) { struct rq *task_rq; u32 reason; p = nldsq_cursor_next_task(&cursor, dsq); if (!p) break; if (!user_task_should_reenq(p, reenq_flags, &reason)) continue; task_rq = task_rq(p); if (locked_rq != task_rq) { if (locked_rq) { scx_rq_lock_drop(locked_rq); raw_spin_rq_unlock(locked_rq); } if (unlikely(!raw_spin_rq_trylock(task_rq))) { raw_spin_unlock(&dsq->lock); raw_spin_rq_lock(task_rq); raw_spin_lock(&dsq->lock); } locked_rq = task_rq; /* did we lose @p while switching locks? */ if (nldsq_cursor_lost_task(&cursor, task_rq, dsq, p)) continue; } /* @p is on @dsq, its rq and @dsq are locked */ dispatch_dequeue_locked(p, dsq); raw_spin_unlock(&dsq->lock); if (WARN_ON_ONCE(p->scx.flags & SCX_TASK_REENQ_REASON_MASK)) p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK; p->scx.flags |= reason; scx_do_enqueue_task(task_rq, p, SCX_ENQ_REENQ, -1); p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK; if (!(++nr_enqueued % SCX_TASK_ITER_BATCH)) { scx_rq_lock_drop(locked_rq); raw_spin_rq_unlock(locked_rq); locked_rq = NULL; cpu_relax(); } raw_spin_lock(&dsq->lock); } list_del_init(&cursor.node); raw_spin_unlock(&dsq->lock); if (locked_rq != rq) { if (locked_rq) { scx_rq_lock_drop(locked_rq); raw_spin_rq_unlock(locked_rq); } raw_spin_rq_lock(rq); } } static void process_deferred_reenq_users(struct rq *rq) { lockdep_assert_rq_held(rq); while (true) { struct scx_dispatch_q *dsq; u64 dsq_id, reenq_flags; scoped_guard (raw_spinlock, &rq->scx.deferred_reenq_lock) { struct scx_deferred_reenq_user *dru = list_first_entry_or_null(&rq->scx.deferred_reenq_users, struct scx_deferred_reenq_user, node); struct scx_dsq_pcpu *dsq_pcpu; if (!dru) return; dsq_pcpu = container_of(dru, struct scx_dsq_pcpu, deferred_reenq_user); dsq = dsq_pcpu->dsq; reenq_flags = dru->flags; WRITE_ONCE(dru->flags, 0); list_del_init(&dru->node); } /* see schedule_dsq_reenq() */ smp_mb(); /* destroy_dsq() may have raced and invalidated @dsq, nothing to reenq */ dsq_id = READ_ONCE(dsq->id); if (unlikely(dsq_id == SCX_DSQ_INVALID)) continue; BUG_ON(dsq_id & SCX_DSQ_FLAG_BUILTIN); reenq_user(rq, dsq, reenq_flags); } } static void run_deferred(struct rq *rq) { process_ddsp_deferred_locals(rq); if (!list_empty(&rq->scx.deferred_reenq_locals)) process_deferred_reenq_locals(rq); if (!list_empty(&rq->scx.deferred_reenq_users)) process_deferred_reenq_users(rq); scx_reenq_reject(rq); } #ifdef CONFIG_NO_HZ_FULL bool scx_can_stop_tick(struct rq *rq) { struct task_struct *p = rq->curr; struct scx_sched *sch = scx_task_sched(p); if (p->sched_class != &ext_sched_class) return true; /* * @rq->curr may still reference an outgoing EXT task after it has been * dequeued. If no EXT tasks are accounted on @rq, ignore its stale * slice state. If another task is dispatched from a DSQ, * set_next_task_scx() will update the dependency for the incoming task. */ if (!rq->scx.nr_running) return true; if (scx_bypassing(sch, cpu_of(rq))) return false; /* * A running rescuee's charging and expiry are tick-driven, see * scx_rescue_charge(). Keep the tick while rescue is in progress. */ if (unlikely(p == scx_rescuee(rq))) return false; /* * @rq can dispatch from different DSQs, so we can't tell whether it * needs the tick or not by looking at nr_running. Allow stopping ticks * iff the BPF scheduler indicated so. See set_next_task_scx(). */ return rq->scx.flags & SCX_RQ_CAN_STOP_TICK; } #endif #ifdef CONFIG_EXT_GROUP_SCHED DEFINE_STATIC_PERCPU_RWSEM(scx_cgroup_ops_rwsem); void scx_tg_init(struct task_group *tg) { tg->scx.weight = CGROUP_WEIGHT_DFL; tg->scx.bw_period_us = default_bw_period_us(); tg->scx.bw_quota_us = RUNTIME_INF; tg->scx.idle = false; } /** * scx_tg_sched - Resolve a task_group's sched * @tg: task_group of interest * * Return the sched that @tg's ops.cgroup_init() succeeded on, %NULL if @tg * isn't inited. An autogroup tg has no cgroup of its own and resolves to the * root sched. * * When a child sched exits, its task_groups are moved to the parent and * re-inited on it. A failed re-init fails the parent in turn and leaves the * task_group without a sched it's inited on, resolving to %NULL. See * scx_cgroup_return_subtree(). * * Safe for callers read-locking the ops rwsem. tg->scx.sched rewrites * write-lock it, and tg on/offline can't overlap such callers as a css's files * are created after online and drained before offline. */ static struct scx_sched *scx_tg_sched(struct task_group *tg) { lockdep_assert(lockdep_is_held(&cgroup_mutex) || lockdep_is_held(&scx_cgroup_ops_rwsem)); if (!tg->css.cgroup) tg = &root_task_group; /* INITED means ops.cgroup_init() succeeded on @tg->scx.sched */ return (tg->scx.flags & SCX_TG_INITED) ? tg->scx.sched : NULL; } /** * scx_tg_knob_sched - Resolve the sched receiving a task_group's knob updates * @tg: task_group of interest * * Knobs of a cgroup belong to the parent. Deliver the set_* ops to the * parent task_group's sched, which equals @tg's own sched everywhere except * at a sub-scheduler attach point, where the sub's parent sched receives * them. * * Return %NULL if the parent task_group has no sched. That can happen when the * parent's ops.cgroup_init() fails while a sub-scheduler is being disabled. * * The callers sit in @tg's cgroup file writes holding the ops rwsem read * side. That extends scx_tg_sched()'s file-write argument to the parent's * sched read: a parent css outlives its children's files. */ static struct scx_sched *scx_tg_knob_sched(struct task_group *tg) { lockdep_assert(lockdep_is_held(&cgroup_mutex) || lockdep_is_held(&scx_cgroup_ops_rwsem)); if (!tg->css.cgroup || !tg->css.parent) return scx_tg_sched(&root_task_group); return scx_tg_sched(css_tg(tg->css.parent)); } int scx_tg_online(struct task_group *tg) { int ret = 0; WARN_ON_ONCE(tg->scx.flags & (SCX_TG_ONLINE | SCX_TG_INITED)); if (scx_cgroup_enabled) { struct scx_sched *sch; /* * The cgroup lifetime notifier populates cgrp->scx_sched before * css_online, but only on the default hierarchy. Sub-scheds are * attached to the cgroup2 hierarchy, so a cgroup1 task_group * always belongs to the root sched. */ if (cgroup_on_dfl(tg->css.cgroup)) sch = scx_cgroup_sched(tg->css.cgroup); else sch = scx_tg_sched(&root_task_group); if (SCX_HAS_OP(sch, cgroup_init)) { struct scx_cgroup_init_args args = { .weight = tg->scx.weight, .bw_period_us = tg->scx.bw_period_us, .bw_quota_us = tg->scx.bw_quota_us, .bw_burst_us = tg->scx.bw_burst_us }; ret = SCX_CALL_OP_RET(sch, cgroup_init, NULL, tg->css.cgroup, &args); if (ret) ret = scx_ops_sanitize_err(sch, "cgroup_init", ret); } if (ret == 0) { tg->scx.sched = sch; tg->scx.flags |= SCX_TG_ONLINE | SCX_TG_INITED; } } else { tg->scx.flags |= SCX_TG_ONLINE; } return ret; } void scx_tg_offline(struct task_group *tg) { struct scx_sched *sch = tg->scx.sched; WARN_ON_ONCE(!(tg->scx.flags & SCX_TG_ONLINE)); /* INITED implies non-NULL @sch, test before SCX_HAS_OP() derefs */ if (scx_cgroup_enabled && (tg->scx.flags & SCX_TG_INITED) && SCX_HAS_OP(sch, cgroup_exit)) SCX_CALL_OP(sch, cgroup_exit, NULL, tg->css.cgroup); tg->scx.sched = NULL; tg->scx.flags &= ~(SCX_TG_ONLINE | SCX_TG_INITED); } /* * @p's sched for the cgroup migration paths. Stable as re-homes happen either * at CGROUP_TASK_MIGRATED of the same migration or under scx_cgroup_lock(), * both while holding cgroup_mutex. */ static struct scx_sched *scx_cgroup_task_sched(struct task_struct *p) { return rcu_dereference_protected(p->scx.sched, lockdep_is_held(&cgroup_mutex)); } int scx_cgroup_can_attach(struct cgroup_taskset *tset) { struct cgroup_subsys_state *css; struct task_struct *p; int ret; if (!scx_cgroup_enabled) return 0; cgroup_taskset_for_each(p, css, tset) { struct scx_sched *sch = scx_cgroup_task_sched(p); struct cgroup *from = tg_cgrp(task_group(p)); struct cgroup *to = tg_cgrp(css_tg(css)); WARN_ON_ONCE(p->scx.cgrp_moving_from); /* * sched_move_task() omits identity migrations. Let's match the * behavior so that ops.cgroup_prep_move() and ops.cgroup_move() * always match one-to-one. */ if (from == to) continue; /* * The cgroup_move ops are delivered to @p's sched, and only for * moves that don't re-home @p. A re-homing move changes the dfl * cgroup's sched and is reported through the * exit_task/init_task pair that the re-homing generates. */ if (!sch || sch != scx_cgroup_sched(task_css_set(p)->mg_dst_cset->dfl_cgrp)) continue; if (SCX_HAS_OP(sch, cgroup_prep_move)) { ret = SCX_CALL_OP_RET(sch, cgroup_prep_move, NULL, p, from, css->cgroup); if (ret) { ret = scx_ops_sanitize_err(sch, "cgroup_prep_move", ret); goto err; } } p->scx.cgrp_moving_from = from; } return 0; err: cgroup_taskset_for_each(p, css, tset) { struct scx_sched *sch = scx_cgroup_task_sched(p); /* cgrp_moving_from implies non-NULL @sch, test it first */ if (p->scx.cgrp_moving_from && SCX_HAS_OP(sch, cgroup_cancel_move)) SCX_CALL_OP(sch, cgroup_cancel_move, NULL, p, p->scx.cgrp_moving_from, css->cgroup); p->scx.cgrp_moving_from = NULL; } return ret; } void scx_cgroup_move_task(struct task_struct *p) { struct scx_sched *sch; if (!scx_cgroup_enabled) return; /* * Migration keys off css rather than cgroup identity, so it can hand an * unchanged-cgroup task here with cgrp_moving_from NULL. Nothing to * report to the BPF scheduler then, so skip it and keep prep_move and * move paired. */ sch = scx_cgroup_task_sched(p); if (p->scx.cgrp_moving_from && SCX_HAS_OP(sch, cgroup_move)) SCX_CALL_OP_TASK(sch, cgroup_move, task_rq(p), p, p->scx.cgrp_moving_from, tg_cgrp(task_group(p))); p->scx.cgrp_moving_from = NULL; } void scx_cgroup_cancel_attach(struct cgroup_taskset *tset) { struct cgroup_subsys_state *css; struct task_struct *p; if (!scx_cgroup_enabled) return; cgroup_taskset_for_each(p, css, tset) { struct scx_sched *sch = scx_cgroup_task_sched(p); /* cgrp_moving_from implies non-NULL @sch, test it first */ if (p->scx.cgrp_moving_from && SCX_HAS_OP(sch, cgroup_cancel_move)) SCX_CALL_OP(sch, cgroup_cancel_move, NULL, p, p->scx.cgrp_moving_from, css->cgroup); p->scx.cgrp_moving_from = NULL; } } void scx_group_set_weight(struct task_group *tg, unsigned long weight) { struct scx_sched *sch; percpu_down_read(&scx_cgroup_ops_rwsem); sch = scx_tg_knob_sched(tg); if (scx_cgroup_enabled && sch && SCX_HAS_OP(sch, cgroup_set_weight) && tg->scx.weight != weight) SCX_CALL_OP(sch, cgroup_set_weight, NULL, tg_cgrp(tg), weight); tg->scx.weight = weight; percpu_up_read(&scx_cgroup_ops_rwsem); } void scx_group_set_idle(struct task_group *tg, bool idle) { struct scx_sched *sch; percpu_down_read(&scx_cgroup_ops_rwsem); sch = scx_tg_knob_sched(tg); if (scx_cgroup_enabled && sch && SCX_HAS_OP(sch, cgroup_set_idle)) SCX_CALL_OP(sch, cgroup_set_idle, NULL, tg_cgrp(tg), idle); /* Update the task group's idle state */ tg->scx.idle = idle; percpu_up_read(&scx_cgroup_ops_rwsem); } void scx_group_set_bandwidth(struct task_group *tg, u64 period_us, u64 quota_us, u64 burst_us) { struct scx_sched *sch; percpu_down_read(&scx_cgroup_ops_rwsem); sch = scx_tg_knob_sched(tg); if (scx_cgroup_enabled && sch && SCX_HAS_OP(sch, cgroup_set_bandwidth) && (tg->scx.bw_period_us != period_us || tg->scx.bw_quota_us != quota_us || tg->scx.bw_burst_us != burst_us)) SCX_CALL_OP(sch, cgroup_set_bandwidth, NULL, tg_cgrp(tg), period_us, quota_us, burst_us); tg->scx.bw_period_us = period_us; tg->scx.bw_quota_us = quota_us; tg->scx.bw_burst_us = burst_us; percpu_up_read(&scx_cgroup_ops_rwsem); } #endif /* CONFIG_EXT_GROUP_SCHED */ #if defined(CONFIG_EXT_GROUP_SCHED) || defined(CONFIG_EXT_SUB_SCHED) static struct cgroup *root_cgroup(void) { return &cgrp_dfl_root.cgrp; } /* * cgroup_lock() must nest outside the rwsem write side: a writer waiting * for cgroup_mutex deadlocks with cgroup teardown, which holds it while * draining a set_* file write blocked on the rwsem behind the writer. */ void scx_cgroup_lock(void) { cgroup_lock(); #ifdef CONFIG_EXT_GROUP_SCHED percpu_down_write(&scx_cgroup_ops_rwsem); #endif } void scx_cgroup_unlock(void) { #ifdef CONFIG_EXT_GROUP_SCHED percpu_up_write(&scx_cgroup_ops_rwsem); #endif cgroup_unlock(); } #else /* CONFIG_EXT_GROUP_SCHED || CONFIG_EXT_SUB_SCHED */ static inline struct cgroup *root_cgroup(void) { return NULL; } static inline void scx_cgroup_lock(void) {} static inline void scx_cgroup_unlock(void) {} #endif /* CONFIG_EXT_GROUP_SCHED || CONFIG_EXT_SUB_SCHED */ /* * Omitted operations: * * - migrate_task_rq: Unnecessary as task to cpu mapping is transient. * * - task_fork/dead: We need fork/dead notifications for all tasks regardless of * their current sched_class. Call them directly from sched core instead. */ DEFINE_SCHED_CLASS(ext) = { .enqueue_task = enqueue_task_scx, .dequeue_task = dequeue_task_scx, .yield_task = yield_task_scx, .yield_to_task = yield_to_task_scx, .wakeup_preempt = wakeup_preempt_scx, .pick_task = pick_task_scx, .put_prev_task = put_prev_task_scx, .set_next_task = set_next_task_scx, .select_task_rq = select_task_rq_scx, .task_woken = task_woken_scx, .set_cpus_allowed = set_cpus_allowed_scx, .rq_online = rq_online_scx, .rq_offline = rq_offline_scx, .task_tick = task_tick_scx, .switching_to = switching_to_scx, .switched_from = switched_from_scx, .switched_to = switched_to_scx, .reweight_task = reweight_task_scx, .prio_changed = prio_changed_scx, .update_curr = update_curr_scx, #ifdef CONFIG_UCLAMP_TASK .uclamp_enabled = 1, #endif }; s32 scx_init_dsq(struct scx_dispatch_q *dsq, u64 dsq_id, struct scx_sched *sch) { s32 cpu; memset(dsq, 0, sizeof(*dsq)); raw_spin_lock_init(&dsq->lock); INIT_LIST_HEAD(&dsq->list); dsq->id = dsq_id; dsq->sched = sch; dsq->pcpu = alloc_percpu(struct scx_dsq_pcpu); if (!dsq->pcpu) return -ENOMEM; for_each_possible_cpu(cpu) { struct scx_dsq_pcpu *pcpu = per_cpu_ptr(dsq->pcpu, cpu); pcpu->dsq = dsq; INIT_LIST_HEAD(&pcpu->deferred_reenq_user.node); } return 0; } static void exit_dsq(struct scx_dispatch_q *dsq) { s32 cpu; for_each_possible_cpu(cpu) { struct scx_dsq_pcpu *pcpu = per_cpu_ptr(dsq->pcpu, cpu); struct scx_deferred_reenq_user *dru = &pcpu->deferred_reenq_user; struct rq *rq = cpu_rq(cpu); /* * There must have been a RCU grace period since the last * insertion and @dsq should be off the deferred list by now. */ if (WARN_ON_ONCE(!list_empty(&dru->node))) { guard(raw_spinlock_irqsave)(&rq->scx.deferred_reenq_lock); list_del_init(&dru->node); } } free_percpu(dsq->pcpu); } static void free_dsq_rcufn(struct rcu_head *rcu) { struct scx_dispatch_q *dsq = container_of(rcu, struct scx_dispatch_q, rcu); exit_dsq(dsq); kfree(dsq); } static void free_dsq_irq_workfn(struct irq_work *irq_work) { struct llist_node *to_free = llist_del_all(&dsqs_to_free); struct scx_dispatch_q *dsq, *tmp_dsq; llist_for_each_entry_safe(dsq, tmp_dsq, to_free, free_node) call_rcu(&dsq->rcu, free_dsq_rcufn); } static DEFINE_IRQ_WORK(free_dsq_irq_work, free_dsq_irq_workfn); static void destroy_dsq(struct scx_sched *sch, u64 dsq_id) { struct scx_dispatch_q *dsq; unsigned long flags; rcu_read_lock(); dsq = find_user_dsq(sch, dsq_id); if (!dsq) goto out_unlock_rcu; raw_spin_lock_irqsave(&dsq->lock, flags); if (dsq->nr) { scx_error(sch, "attempting to destroy in-use dsq 0x%016llx (nr=%u)", dsq->id, dsq->nr); goto out_unlock_dsq; } if (rhashtable_remove_fast(&sch->dsq_hash, &dsq->hash_node, dsq_hash_params)) goto out_unlock_dsq; /* * Mark dead by invalidating ->id to prevent scx_dispatch_enqueue() from * queueing more tasks. As this function can be called from anywhere, * freeing is bounced through an irq work to avoid nesting RCU * operations inside scheduler locks. */ dsq->id = SCX_DSQ_INVALID; if (llist_add(&dsq->free_node, &dsqs_to_free)) irq_work_queue(&free_dsq_irq_work); out_unlock_dsq: raw_spin_unlock_irqrestore(&dsq->lock, flags); out_unlock_rcu: rcu_read_unlock(); } #ifdef CONFIG_EXT_GROUP_SCHED static void scx_cgroup_exit(struct scx_sched *sch) { struct cgroup_subsys_state *css; /* * scx_tg_on/offline() are excluded through cgroup_lock(). If we walk * cgroups and exit all the inited ones, all online cgroups are exited. */ css_for_each_descendant_post(css, &root_task_group.css) { struct task_group *tg = css_tg(css); /* also clear the sched of tgs whose ops.cgroup_init() failed */ tg->scx.sched = NULL; if (tg->scx.flags & SCX_TG_INITED) { tg->scx.flags &= ~SCX_TG_INITED; if (sch->ops.cgroup_exit) SCX_CALL_OP(sch, cgroup_exit, NULL, css->cgroup); } } } static int scx_cgroup_init(struct scx_sched *sch) { struct cgroup_subsys_state *css; int ret; /* * scx_tg_on/offline() are excluded through cgroup_lock(). If we walk * cgroups and init, all online cgroups are initialized. */ css_for_each_descendant_pre(css, &root_task_group.css) { struct task_group *tg = css_tg(css); if ((tg->scx.flags & (SCX_TG_ONLINE | SCX_TG_INITED)) != SCX_TG_ONLINE) continue; if (sch->ops.cgroup_init) { struct scx_cgroup_init_args args = { .weight = tg->scx.weight, .bw_period_us = tg->scx.bw_period_us, .bw_quota_us = tg->scx.bw_quota_us, .bw_burst_us = tg->scx.bw_burst_us, }; ret = SCX_CALL_OP_RET(sch, cgroup_init, NULL, css->cgroup, &args); if (ret) { scx_error(sch, "ops.cgroup_init() failed (%d)", ret); return ret; } } tg->scx.sched = sch; tg->scx.flags |= SCX_TG_INITED; } return 0; } #else static void scx_cgroup_exit(struct scx_sched *sch) {} static int scx_cgroup_init(struct scx_sched *sch) { return 0; } #endif /******************************************************************************** * Sysfs interface and ops enable/disable. */ #define SCX_ATTR(_name) \ static struct kobj_attribute scx_attr_##_name = { \ .attr = { .name = __stringify(_name), .mode = 0444 }, \ .show = scx_attr_##_name##_show, \ } static ssize_t scx_attr_state_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { return sysfs_emit(buf, "%s\n", scx_enable_state_str[scx_enable_state()]); } SCX_ATTR(state); static ssize_t scx_attr_switch_all_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { return sysfs_emit(buf, "%d\n", READ_ONCE(scx_switching_all)); } SCX_ATTR(switch_all); static ssize_t scx_attr_nr_rejected_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_nr_rejected)); } SCX_ATTR(nr_rejected); static ssize_t scx_attr_hotplug_seq_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_hotplug_seq)); } SCX_ATTR(hotplug_seq); static ssize_t scx_attr_enable_seq_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_enable_seq)); } SCX_ATTR(enable_seq); static struct attribute *scx_global_attrs[] = { &scx_attr_state.attr, &scx_attr_switch_all.attr, &scx_attr_nr_rejected.attr, &scx_attr_hotplug_seq.attr, &scx_attr_enable_seq.attr, NULL, }; static const struct attribute_group scx_global_attr_group = { .attrs = scx_global_attrs, }; static void free_pnode(struct scx_sched_pnode *pnode); static void free_exit_info(struct scx_exit_info *ei); static const char *scx_exit_reason(enum scx_exit_kind kind); static bool scx_claim_exit(struct scx_sched *sch, enum scx_exit_kind kind); s32 scx_set_cmask_scratch_alloc(struct scx_sched *sch) { size_t size = struct_size_t(struct scx_cmask, bits, SCX_CMASK_NR_WORDS(num_possible_cpus())); int cpu; if (!sch->is_cid_type || !sch->arena_pool) return 0; sch->set_cmask_scratch = alloc_percpu(struct scx_cmask *); if (!sch->set_cmask_scratch) return -ENOMEM; for_each_possible_cpu(cpu) { struct scx_cmask **slot = per_cpu_ptr(sch->set_cmask_scratch, cpu); *slot = scx_arena_alloc(sch, size); if (!*slot) return -ENOMEM; scx_cmask_init(*slot, 0, num_possible_cpus()); } return 0; } static void scx_set_cmask_scratch_free(struct scx_sched *sch) { size_t size = struct_size_t(struct scx_cmask, bits, SCX_CMASK_NR_WORDS(num_possible_cpus())); int cpu; if (!sch->set_cmask_scratch) return; for_each_possible_cpu(cpu) { struct scx_cmask **slot = per_cpu_ptr(sch->set_cmask_scratch, cpu); scx_arena_free(sch, *slot, size); } free_percpu(sch->set_cmask_scratch); sch->set_cmask_scratch = NULL; } static void scx_sched_free_rcu_work(struct work_struct *work) { struct rcu_work *rcu_work = to_rcu_work(work); struct scx_sched *sch = container_of(rcu_work, struct scx_sched, rcu_work); struct rhashtable_iter rht_iter; struct scx_dispatch_q *dsq; int cpu, node; irq_work_sync(&sch->propagate_exit_irq_work); irq_work_sync(&sch->disable_irq_work); kthread_destroy_worker(sch->helper); timer_shutdown_sync(&sch->bypass_lb_timer); free_cpumask_var(sch->bypass_lb_donee_cpumask); free_cpumask_var(sch->bypass_lb_resched_cpumask); free_cpumask_var(sch->stall_cpus); #ifdef CONFIG_EXT_SUB_SCHED kfree(sch->cgrp_path); if (sch_cgroup(sch)) cgroup_put(sch_cgroup(sch)); if (sch->sub_kset) kobject_put(&sch->sub_kset->kobj); if (scx_parent(sch)) kobject_put(&scx_parent(sch)->kobj); #endif /* CONFIG_EXT_SUB_SCHED */ for_each_possible_cpu(cpu) { struct scx_sched_pcpu *pcpu = per_cpu_ptr(sch->pcpu, cpu); /* * $sch would have entered bypass mode before the RCU grace * period. As that blocks new deferrals, all * deferred_reenq_local_node's must be off-list by now. */ WARN_ON_ONCE(!list_empty(&pcpu->deferred_reenq_local.node)); /* remove the queued ecaps sync so the pcpu can be freed */ scx_discard_ecaps_to_sync(cpu, pcpu); /* * Bypass blocks new kicks. Flush the kick irq_work so this * pcpu's to_kick_node is off the list before it is freed. */ irq_work_sync(&cpu_rq(cpu)->scx.kick_cpus_irq_work); WARN_ON_ONCE(!list_empty(&pcpu->to_kick_node)); free_cpumask_var(pcpu->cpus_to_kick); free_cpumask_var(pcpu->cpus_to_kick_if_idle); free_cpumask_var(pcpu->cpus_to_preempt); free_cpumask_var(pcpu->cpus_to_wait); exit_dsq(scx_bypass_dsq(sch, cpu)); } free_percpu(sch->pcpu); for_each_node_state(node, N_POSSIBLE) free_pnode(sch->pnode[node]); kfree(sch->pnode); scx_free_pshards(sch); rhashtable_walk_enter(&sch->dsq_hash, &rht_iter); do { rhashtable_walk_start(&rht_iter); while (!IS_ERR_OR_NULL((dsq = rhashtable_walk_next(&rht_iter)))) destroy_dsq(sch, dsq->id); rhashtable_walk_stop(&rht_iter); } while (dsq == ERR_PTR(-EAGAIN)); rhashtable_walk_exit(&rht_iter); rhashtable_free_and_destroy(&sch->dsq_hash, NULL, NULL); free_exit_info(sch->exit_info); scx_set_cmask_scratch_free(sch); scx_arena_pool_destroy(sch); if (sch->arena_map) bpf_map_put(sch->arena_map); /* @sch is completely inactive by now */ scx_dec_has_subs(sch); kfree(sch); } static void scx_kobj_release(struct kobject *kobj) { struct scx_sched *sch = container_of(kobj, struct scx_sched, kobj); INIT_RCU_WORK(&sch->rcu_work, scx_sched_free_rcu_work); queue_rcu_work(system_dfl_wq, &sch->rcu_work); } static ssize_t scx_attr_ops_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { struct scx_sched *sch = container_of(kobj, struct scx_sched, kobj); return sysfs_emit(buf, "%s\n", sch->ops.name); } SCX_ATTR(ops); #define scx_attr_event_show(buf, at, events, kind) ({ \ sysfs_emit_at(buf, at, "%s %llu\n", #kind, (events)->kind); \ }) static ssize_t scx_attr_events_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { struct scx_sched *sch = container_of(kobj, struct scx_sched, kobj); struct scx_event_stats events; int at = 0; scx_read_events(sch, &events); #define SCX_EVENT(name) (at += scx_attr_event_show(buf, at, &events, name)) SCX_EVENTS_LIST(SCX_EVENT); #undef SCX_EVENT return at; } SCX_ATTR(events); #ifdef CONFIG_EXT_SUB_SCHED static const char *scx_cap_names[__SCX_NR_CAPS] = { [__SCX_CAP_ENQ_IMMED] = "enq_immed", [__SCX_CAP_ENQ] = "enq", [__SCX_CAP_PREEMPT] = "preempt", [__SCX_CAP_PERF] = "perf", }; static ssize_t scx_attr_caps_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { struct scx_sched *sch = container_of(kobj, struct scx_sched, kobj); u32 npossible = num_possible_cpus(); struct scx_cmask *agg __free(kfree) = kzalloc(struct_size(agg, bits, SCX_CMASK_NR_WORDS(npossible)), GFP_KERNEL); unsigned long *agg_bm __free(bitmap) = bitmap_zalloc(npossible, GFP_KERNEL); ssize_t count = 0; s32 cap, si; if (!agg || !agg_bm) return -ENOMEM; for (cap = 0; cap < __SCX_NR_CAPS; cap++) { SCX_CMASK_DEFINE(snap, 0, SCX_CID_SHARD_MAX_CPUS); scx_cmask_init(agg, 0, npossible); for (si = 0; si < sch->nr_pshards; si++) { struct scx_cmask *cm = &sch->pshard[si]->caps[cap].cmask; scx_cmask_reframe(snap, cm->base, cm->nr_cids); scx_cmask_copy(snap, cm); scx_cmask_or(agg, snap); } /* %*pbl takes unsigned long bitmap layout, convert from u64 */ bitmap_from_arr64(agg_bm, agg->bits, npossible); count += sysfs_emit_at(buf, count, "%s: %*pbl\n", scx_cap_names[cap], npossible, agg_bm); } return count; } SCX_ATTR(caps); #endif /* CONFIG_EXT_SUB_SCHED */ static struct attribute *scx_sched_attrs[] = { &scx_attr_ops.attr, &scx_attr_events.attr, #ifdef CONFIG_EXT_SUB_SCHED &scx_attr_caps.attr, #endif NULL, }; ATTRIBUTE_GROUPS(scx_sched); static const struct kobj_type scx_ktype = { .release = scx_kobj_release, .sysfs_ops = &kobj_sysfs_ops, .default_groups = scx_sched_groups, }; static int scx_uevent(const struct kobject *kobj, struct kobj_uevent_env *env) { const struct scx_sched *sch; /* * scx_uevent() can be reached by both scx_sched kobjects (scx_ktype) * and sub-scheduler kset kobjects (kset_ktype) through the parent * chain walk. Filter out the latter to avoid invalid casts. */ if (kobj->ktype != &scx_ktype) return 0; sch = container_of(kobj, struct scx_sched, kobj); return add_uevent_var(env, "SCXOPS=%s", sch->ops.name); } static const struct kset_uevent_ops scx_uevent_ops = { .uevent = scx_uevent, }; /* * Used by sched_fork() and __setscheduler_prio() to pick the matching * sched_class. dl/rt are already handled. */ bool task_should_scx(int policy) { /* if disabled, nothing should be on it */ if (!scx_enabled()) return false; /* scx is taking over all SCHED_OTHER and SCHED_EXT tasks */ if (READ_ONCE(scx_switching_all)) return true; /* * scx is tearing down - keep new SCHED_EXT tasks out. * * Must come after scx_switching_all test, which serves as a proxy * for __scx_switched_all. While __scx_switched_all is set, we must * return true via the branch above: a fork routed to fair would * stall because next_active_class() skips fair. * * This can develop into a deadlock - scx holds scx_enable_mutex across * kthread_create() in scx_alloc_and_add_sched(); if the new kthread is * the stalled task, the disable path can never grab the mutex to clear * scx_switching_all. */ if (unlikely(scx_enable_state() == SCX_DISABLING)) return false; return policy == SCHED_EXT; } bool scx_allow_ttwu_queue(const struct task_struct *p) { struct scx_sched *sch; if (!scx_enabled()) return true; sch = scx_task_sched(p); if (unlikely(!sch)) return true; if (sch->ops.flags & SCX_OPS_ALLOW_QUEUED_WAKEUP) return true; if (unlikely(p->sched_class != &ext_sched_class)) return true; return false; } /** * handle_lockup - sched_ext common lockup handler * @exit_cpu: CPU to record in exit_info. Pass the stalled/hung CPU, not current. * @fmt: format string * * Called on system stall or lockup condition and initiates abort of sched_ext * if enabled, which may resolve the reported lockup. * * Returns %true if sched_ext is enabled and abort was initiated, which may * resolve the lockup. %false if sched_ext is not enabled or abort was already * initiated by someone else. */ static __printf(2, 3) bool handle_lockup(int exit_cpu, const char *fmt, ...) { struct scx_sched *sch; va_list args; bool ret; guard(rcu)(); sch = rcu_dereference(scx_root); if (unlikely(!sch)) return false; switch (scx_enable_state()) { case SCX_ENABLING: case SCX_ENABLED: va_start(args, fmt); ret = scx_vexit(sch, SCX_EXIT_ERROR, 0, exit_cpu, fmt, args); va_end(args); return ret; default: return false; } } /** * scx_rcu_cpu_stall - sched_ext RCU CPU stall handler * @stalled_mask: bit mask of stalled CPUs * * While there are various reasons why RCU CPU stalls can occur on a system * that may not be caused by the current BPF scheduler, try kicking out the * current scheduler in an attempt to recover the system to a good state before * issuing panics. * * Returns %true if sched_ext is enabled and abort was initiated, which may * resolve the reported RCU stall. %false if sched_ext is not enabled or someone * else already initiated abort. */ bool scx_rcu_cpu_stall(const struct cpumask *stalled_mask) { struct scx_sched *sch; struct scx_exit_info *ei; int exit_cpu; guard(rcu)(); sch = rcu_dereference(scx_root); if (unlikely(!sch)) return false; switch (scx_enable_state()) { case SCX_ENABLING: case SCX_ENABLED: break; default: return false; } exit_cpu = cpumask_empty(stalled_mask) ? -1 : (int)cpumask_first(stalled_mask); ei = sch->exit_info; guard(preempt)(); if (!scx_claim_exit(sch, SCX_EXIT_ERROR)) return false; #ifdef CONFIG_STACKTRACE ei->bt_len = stack_trace_save(ei->bt, SCX_EXIT_BT_LEN, 1); #endif scnprintf(ei->msg, SCX_EXIT_MSG_LEN, "RCU CPU stall on CPUs (%*pbl)", cpumask_pr_args(stalled_mask)); ei->kind = SCX_EXIT_ERROR; ei->reason = scx_exit_reason(SCX_EXIT_ERROR); ei->exit_cpu = exit_cpu; cpumask_copy(sch->stall_cpus, stalled_mask); irq_work_queue(&sch->disable_irq_work); return true; } /** * scx_softlockup - sched_ext softlockup handler * @dur_s: number of seconds of CPU stuck due to soft lockup * * On some multi-socket setups (e.g. 2x Intel 8480c), the BPF scheduler can * live-lock the system by making many CPUs target the same DSQ to the point * where soft-lockup detection triggers. This function is called from * soft-lockup watchdog when the triggering point is close and tries to unjam * the system and aborting the BPF scheduler. */ void scx_softlockup(u32 dur_s) { int cpu = smp_processor_id(); if (!handle_lockup(cpu, "soft lockup - CPU %d stuck for %us", cpu, dur_s)) return; printk_deferred(KERN_ERR "sched_ext: Soft lockup - CPU %d stuck for %us, disabling BPF scheduler\n", cpu, dur_s); } /** * scx_hardlockup - sched_ext hardlockup handler * @cpu: the target CPU * * A poorly behaving BPF scheduler can trigger hard lockup by e.g. putting * numerous affinitized tasks in a single queue and directing all CPUs at it. * Try kicking out the current scheduler in an attempt to recover the system to * a good state before taking more drastic actions. * * Called from NMI. Aborting the scheduler sets ->aborting throughout the * hierarchy before returning, which is what breaks the dispatch-path live-locks * that can hard-lock CPUs. * * Returns %true if sched_ext is enabled and abort was initiated, which may * resolve the lockup. %false if sched_ext is not enabled or abort was already * initiated by someone else. */ bool scx_hardlockup(int cpu) { if (!handle_lockup(cpu, "hard lockup - CPU %d", cpu)) return false; printk_deferred(KERN_ERR "sched_ext: Hard lockup - CPU %d, disabling BPF scheduler\n", cpu); return true; } static u32 bypass_lb_cpu(struct scx_sched *sch, s32 donor, struct cpumask *donee_mask, struct cpumask *resched_mask, u32 nr_donor_target, u32 nr_donee_target) { struct rq *donor_rq = cpu_rq(donor); struct scx_dispatch_q *donor_dsq = scx_bypass_dsq(sch, donor); struct task_struct *p, *n; struct scx_dsq_list_node cursor = INIT_DSQ_LIST_CURSOR(cursor, donor_dsq, 0); s32 delta = READ_ONCE(donor_dsq->nr) - nr_donor_target; u32 nr_balanced = 0, min_delta_us; /* * All we want to guarantee is reasonable forward progress. No reason to * fine tune. Assuming every task on @donor_dsq runs their full slice, * consider offloading iff the total queued duration is over the * threshold. */ min_delta_us = READ_ONCE(scx_bypass_lb_intv_us) / SCX_BYPASS_LB_MIN_DELTA_DIV; if (delta < DIV_ROUND_UP(min_delta_us, READ_ONCE(scx_slice_bypass_us))) return 0; raw_spin_rq_lock_irq(donor_rq); raw_spin_lock(&donor_dsq->lock); list_add(&cursor.node, &donor_dsq->list); resume: n = container_of(&cursor, struct task_struct, scx.dsq_list); n = nldsq_next_task(donor_dsq, n, false); while ((p = n)) { struct scx_dispatch_q *donee_dsq; int donee; n = nldsq_next_task(donor_dsq, n, false); if (donor_dsq->nr <= nr_donor_target) break; if (cpumask_empty(donee_mask)) break; /* * If an earlier pass placed @p on @donor_dsq from a different * CPU and the donee hasn't consumed it yet, @p is still on the * previous CPU and task_rq(@p) != @donor_rq. @p can't be moved * without its rq locked. Skip. */ if (task_rq(p) != donor_rq) continue; donee = cpumask_any_and_distribute(donee_mask, p->cpus_ptr); if (donee >= nr_cpu_ids) continue; donee_dsq = scx_bypass_dsq(sch, donee); /* * $p's rq is not locked but $p's DSQ lock protects its * scheduling properties making this test safe. */ if (!task_can_run_on_remote_rq(sch, p, cpu_rq(donee), false)) continue; /* * Moving $p from one non-local DSQ to another. The source rq * and DSQ are already locked. Do an abbreviated dequeue and * then perform enqueue without unlocking $donor_dsq. * * We don't want to drop and reacquire the lock on each * iteration as @donor_dsq can be very long and potentially * highly contended. Donee DSQs are less likely to be contended. * The nested locking is safe as only this LB moves tasks * between bypass DSQs. */ dispatch_dequeue_locked(p, donor_dsq); scx_dispatch_enqueue(sch, cpu_rq(donee), donee_dsq, p, 0, 0, SCX_ENQ_NESTED); /* * $donee might have been idle and need to be woken up. No need * to be clever. Kick every CPU that receives tasks. */ cpumask_set_cpu(donee, resched_mask); if (READ_ONCE(donee_dsq->nr) >= nr_donee_target) cpumask_clear_cpu(donee, donee_mask); nr_balanced++; if (!(nr_balanced % SCX_BYPASS_LB_BATCH) && n) { list_move_tail(&cursor.node, &n->scx.dsq_list.node); raw_spin_unlock(&donor_dsq->lock); scx_rq_lock_drop(donor_rq); raw_spin_rq_unlock_irq(donor_rq); cpu_relax(); raw_spin_rq_lock_irq(donor_rq); raw_spin_lock(&donor_dsq->lock); goto resume; } } list_del_init(&cursor.node); raw_spin_unlock(&donor_dsq->lock); scx_rq_lock_drop(donor_rq); raw_spin_rq_unlock_irq(donor_rq); return nr_balanced; } static void bypass_lb_node(struct scx_sched *sch, int node) { const struct cpumask *node_mask = cpumask_of_node(node); struct cpumask *donee_mask = sch->bypass_lb_donee_cpumask; struct cpumask *resched_mask = sch->bypass_lb_resched_cpumask; u32 nr_tasks = 0, nr_cpus = 0, nr_balanced = 0; u32 nr_target, nr_donor_target; u32 before_min = U32_MAX, before_max = 0; u32 after_min = U32_MAX, after_max = 0; int cpu; /* count the target tasks and CPUs */ for_each_cpu_and(cpu, cpu_online_mask, node_mask) { u32 nr = READ_ONCE(scx_bypass_dsq(sch, cpu)->nr); nr_tasks += nr; nr_cpus++; before_min = min(nr, before_min); before_max = max(nr, before_max); } if (!nr_cpus) return; /* * We don't want CPUs to have more than $nr_donor_target tasks and * balancing to fill donee CPUs upto $nr_target. Once targets are * calculated, find the donee CPUs. */ nr_target = DIV_ROUND_UP(nr_tasks, nr_cpus); nr_donor_target = DIV_ROUND_UP(nr_target * SCX_BYPASS_LB_DONOR_PCT, 100); cpumask_clear(donee_mask); for_each_cpu_and(cpu, cpu_online_mask, node_mask) { if (READ_ONCE(scx_bypass_dsq(sch, cpu)->nr) < nr_target) cpumask_set_cpu(cpu, donee_mask); } /* iterate !donee CPUs and see if they should be offloaded */ cpumask_clear(resched_mask); for_each_cpu_and(cpu, cpu_online_mask, node_mask) { if (cpumask_empty(donee_mask)) break; if (cpumask_test_cpu(cpu, donee_mask)) continue; if (READ_ONCE(scx_bypass_dsq(sch, cpu)->nr) <= nr_donor_target) continue; nr_balanced += bypass_lb_cpu(sch, cpu, donee_mask, resched_mask, nr_donor_target, nr_target); } for_each_cpu(cpu, resched_mask) resched_cpu(cpu); for_each_cpu_and(cpu, cpu_online_mask, node_mask) { u32 nr = READ_ONCE(scx_bypass_dsq(sch, cpu)->nr); after_min = min(nr, after_min); after_max = max(nr, after_max); } trace_sched_ext_bypass_lb(node, nr_cpus, nr_tasks, nr_balanced, before_min, before_max, after_min, after_max); } /* * In bypass mode, all tasks are put on the per-CPU bypass DSQs. If the machine * is over-saturated and the BPF scheduler skewed tasks into few CPUs, some * bypass DSQs can be overloaded. If there are enough tasks to saturate other * lightly loaded CPUs, such imbalance can lead to very high execution latency * on the overloaded CPUs and thus to hung tasks and RCU stalls. To avoid such * outcomes, a simple load balancing mechanism is implemented by the following * timer which runs periodically while bypass mode is in effect. */ static void scx_bypass_lb_timerfn(struct timer_list *timer) { struct scx_sched *sch = container_of(timer, struct scx_sched, bypass_lb_timer); int node; u32 intv_us; if (!scx_bypass_dsp_enabled(sch)) return; for_each_node_with_cpus(node) bypass_lb_node(sch, node); intv_us = READ_ONCE(scx_bypass_lb_intv_us); if (intv_us) mod_timer(timer, jiffies + usecs_to_jiffies(intv_us)); } static bool inc_bypass_depth(struct scx_sched *sch) { lockdep_assert_held(&scx_bypass_lock); WARN_ON_ONCE(sch->bypass_depth < 0); WRITE_ONCE(sch->bypass_depth, sch->bypass_depth + 1); if (sch->bypass_depth != 1) return false; WRITE_ONCE(sch->slice_dfl, READ_ONCE(scx_slice_bypass_us) * NSEC_PER_USEC); sch->bypass_timestamp = ktime_get_ns(); scx_add_event(sch, SCX_EV_BYPASS_ACTIVATE, 1); return true; } static bool dec_bypass_depth(struct scx_sched *sch) { lockdep_assert_held(&scx_bypass_lock); WARN_ON_ONCE(sch->bypass_depth < 1); WRITE_ONCE(sch->bypass_depth, sch->bypass_depth - 1); if (sch->bypass_depth != 0) return false; WRITE_ONCE(sch->slice_dfl, SCX_SLICE_DFL); scx_add_event(sch, SCX_EV_BYPASS_DURATION, ktime_get_ns() - sch->bypass_timestamp); return true; } static void enable_bypass_dsp(struct scx_sched *sch) { struct scx_sched *host = scx_parent(sch) ?: sch; u32 intv_us = READ_ONCE(scx_bypass_lb_intv_us); s32 ret; /* * @sch->bypass_depth transitioning from 0 to 1 triggers enabling. * Shouldn't stagger. */ if (WARN_ON_ONCE(test_and_set_bit(0, &sch->bypass_dsp_claim))) return; /* * When a sub-sched bypasses, its tasks are queued on the bypass DSQs of * the nearest non-bypassing ancestor or root. As enable_bypass_dsp() is * called iff @sch is not already bypassed due to an ancestor bypassing, * we can assume that the parent is not bypassing and thus will be the * host of the bypass DSQs. * * While the situation may change in the future, the following * guarantees that the nearest non-bypassing ancestor or root has bypass * dispatch enabled while a descendant is bypassing, which is all that's * required. * * scx_bypass_dsp_enabled() test is used to determine whether to enter * the bypass dispatch handling path from both bypassing and hosting * scheds. Bump enable depth on both @sch and bypass dispatch host. */ ret = atomic_inc_return(&sch->bypass_dsp_enable_depth); WARN_ON_ONCE(ret <= 0); if (host != sch) { ret = atomic_inc_return(&host->bypass_dsp_enable_depth); WARN_ON_ONCE(ret <= 0); } /* * The LB timer will stop running if bypass dispatch is disabled. Start * after enabling bypass dispatch. */ if (intv_us && !timer_pending(&host->bypass_lb_timer)) mod_timer(&host->bypass_lb_timer, jiffies + usecs_to_jiffies(intv_us)); } /* may be called without holding scx_bypass_lock */ void scx_disable_bypass_dsp(struct scx_sched *sch) { s32 ret; if (!test_and_clear_bit(0, &sch->bypass_dsp_claim)) return; ret = atomic_dec_return(&sch->bypass_dsp_enable_depth); WARN_ON_ONCE(ret < 0); if (scx_parent(sch)) { ret = atomic_dec_return(&scx_parent(sch)->bypass_dsp_enable_depth); WARN_ON_ONCE(ret < 0); } } /** * unbypass_renotify_idle - Arm an idle re-notify for a sched leaving bypass * @rq: rq of the cpu leaving bypass * @pos: scheduler that just left bypass on @rq's cpu * @pcpu: @pos's per-cpu state for @rq's cpu * * A sched leaving bypass is owed the ops.update_idle() calls suppressed while * bypassing. A cpu that goes idle during the bypass window and stays idle won't * produce a notification. Arm a re-notify that scx_bypass()'s resched flushes * on the next idle pick. * * An acute case is ops.sub_attach(). If the parent grants the child cids while * attaching, when attach is complete and bypass is lifted, the child may hold * idle cids it never saw go idle. * * The root is no exception as bypass suppresses its notifications the same way. * However, the root uses a separate per-rq flag so its re-notify keeps working * even when !CONFIG_EXT_SUB_SCHED. */ static void unbypass_renotify_idle(struct rq *rq, struct scx_sched *pos, struct scx_sched_pcpu *pcpu) { if (!pos->level) { rq->scx.flags |= SCX_RQ_ROOT_IDLE_RENOTIFY; return; } #ifdef CONFIG_EXT_SUB_SCHED pcpu->idle_renotify = true; rq->scx.flags |= SCX_RQ_SUB_IDLE_RENOTIFY; #endif } /** * scx_bypass - [Un]bypass scx_ops and guarantee forward progress * @sch: sched to bypass * @bypass: true for bypass, false for unbypass * * Bypassing guarantees that all runnable tasks make forward progress without * trusting the BPF scheduler. We can't grab any mutexes or rwsems as they might * be held by tasks that the BPF scheduler is forgetting to run, which * unfortunately also excludes toggling the static branches. * * Let's work around by overriding a couple ops and modifying behaviors based on * the DISABLING state and then cycling the queued tasks through dequeue/enqueue * to force global FIFO scheduling. * * - ops.select_cpu() is ignored and the default select_cpu() is used. * * - ops.enqueue() is ignored and tasks are queued in simple global FIFO order. * %SCX_OPS_ENQ_LAST is also ignored. * * - ops.dispatch() is ignored. * * - dispatch_one() does not report %SCX_DSP_PREV on non-zero slice as slice * can't be trusted. Whenever a tick triggers, the running task is rotated to * the tail of the queue. * * - pick_next_task() suppresses zero slice warning. * * - scx_kick_cpu() is disabled to avoid irq_work malfunction during PM * operations. * * - scx_prio_less() reverts to the default runnable_at order. */ void scx_bypass(struct scx_sched *sch, bool bypass) { struct scx_sched *pos; unsigned long flags; int cpu; raw_spin_lock_irqsave(&scx_bypass_lock, flags); if (bypass) { if (!inc_bypass_depth(sch)) goto unlock; enable_bypass_dsp(sch); } else { if (!dec_bypass_depth(sch)) goto unlock; } /* * Bypass state is propagated to all descendants - an scx_sched bypasses * if itself or any of its ancestors are in bypass mode. */ raw_spin_lock(&scx_sched_lock); scx_for_each_descendant_pre(pos, sch) { if (pos == sch) continue; if (bypass) inc_bypass_depth(pos); else dec_bypass_depth(pos); } raw_spin_unlock(&scx_sched_lock); /* * No task property is changing. We just need to make sure all currently * queued tasks are re-queued according to the new scx_bypassing() * state. As an optimization, walk each rq's runnable_list instead of * the scx_tasks list. * * This function can't trust the scheduler and thus can't use * cpus_read_lock(). Walk all possible CPUs instead of online. */ for_each_possible_cpu(cpu) { struct rq *rq = cpu_rq(cpu); struct task_struct *p, *n; raw_spin_rq_lock(rq); raw_spin_lock(&scx_sched_lock); scx_for_each_descendant_pre(pos, sch) { struct scx_sched_pcpu *pcpu = per_cpu_ptr(pos->pcpu, cpu); bool was_bypassing = pcpu->flags & SCX_SCHED_PCPU_BYPASSING; if (pos->bypass_depth) { pcpu->flags |= SCX_SCHED_PCPU_BYPASSING; } else { pcpu->flags &= ~SCX_SCHED_PCPU_BYPASSING; if (was_bypassing) { unbypass_renotify_idle(rq, pos, pcpu); scx_unbypass_replay_ecaps(rq, pos); } } } raw_spin_unlock(&scx_sched_lock); /* * We need to guarantee that no tasks are on the BPF scheduler * while bypassing. Either we see enabled or the enable path * sees scx_bypassing() before moving tasks to SCX. */ if (!scx_enabled()) { scx_rq_lock_drop(rq); raw_spin_rq_unlock(rq); continue; } /* * The use of list_for_each_entry_safe_reverse() is required * because each task is going to be removed from and added back * to the runnable_list during iteration. Because they're added * to the tail of the list, safe reverse iteration can still * visit all nodes. */ list_for_each_entry_safe_reverse(p, n, &rq->scx.runnable_list, scx.runnable_node) { if (!scx_is_descendant(scx_task_sched(p), sch)) continue; /* * Bypass trumps protection. Cycling clears for queued * tasks but current task needs explicit stripping. */ if (bypass && task_current(rq, p)) scx_task_slice_ended(rq, p); /* cycling deq/enq is enough, see the function comment */ scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) { /* nothing */ ; } } /* resched to restore ticks and idle state */ if (cpu_online(cpu) || cpu == smp_processor_id()) resched_curr(rq); scx_rq_lock_drop(rq); raw_spin_rq_unlock(rq); } /* disarming must come after moving all tasks out of the bypass DSQs */ if (!bypass) scx_disable_bypass_dsp(sch); unlock: raw_spin_unlock_irqrestore(&scx_bypass_lock, flags); } static void free_exit_info(struct scx_exit_info *ei) { kvfree(ei->dump); kfree(ei->msg); kfree(ei->bt); kfree(ei); } static struct scx_exit_info *alloc_exit_info(size_t exit_dump_len) { struct scx_exit_info *ei; ei = kzalloc_obj(*ei); if (!ei) return NULL; ei->exit_cpu = -1; ei->bt = kzalloc_objs(ei->bt[0], SCX_EXIT_BT_LEN); ei->msg = kzalloc(SCX_EXIT_MSG_LEN, GFP_KERNEL); ei->dump = kvzalloc(exit_dump_len, GFP_KERNEL); if (!ei->bt || !ei->msg || !ei->dump) { free_exit_info(ei); return NULL; } return ei; } static const char *scx_exit_reason(enum scx_exit_kind kind) { switch (kind) { case SCX_EXIT_UNREG: return "unregistered from user space"; case SCX_EXIT_UNREG_BPF: return "unregistered from BPF"; case SCX_EXIT_UNREG_KERN: return "unregistered from the main kernel"; case SCX_EXIT_SYSRQ: return "disabled by sysrq-S"; case SCX_EXIT_PARENT: return "parent exiting"; case SCX_EXIT_PARENT_KILL: return "killed by parent scheduler"; case SCX_EXIT_ERROR: return "runtime error"; case SCX_EXIT_ERROR_BPF: return "scx_bpf_error"; case SCX_EXIT_ERROR_STALL: return "runnable task stall"; case SCX_EXIT_ERROR_REENQ: return "reenqueue limit"; case SCX_EXIT_ERROR_RESCUE: return "rescue bandwidth overload"; default: return ""; } } static void free_kick_syncs(void) { int cpu; for_each_possible_cpu(cpu) { struct scx_kick_syncs __rcu **ksyncs = per_cpu_ptr(&scx_kick_syncs, cpu); struct scx_kick_syncs *to_free; /* flush the pending kick before freeing @ksyncs */ irq_work_sync(&cpu_rq(cpu)->scx.kick_cpus_irq_work); to_free = rcu_replace_pointer(*ksyncs, NULL, true); if (to_free) kvfree_rcu(to_free, rcu); } } static void refresh_watchdog(void) { struct scx_sched *sch; unsigned long intv = ULONG_MAX; /* take the shortest timeout and use its half for watchdog interval */ rcu_read_lock(); list_for_each_entry_rcu(sch, &scx_sched_all, all) intv = max(min(intv, sch->watchdog_timeout / 2), 1); rcu_read_unlock(); WRITE_ONCE(scx_watchdog_timestamp, jiffies); WRITE_ONCE(scx_watchdog_interval, intv); if (intv < ULONG_MAX) mod_delayed_work(system_dfl_wq, &scx_watchdog_work, intv); else cancel_delayed_work_sync(&scx_watchdog_work); } s32 scx_link_sched(struct scx_sched *sch) { scoped_guard(raw_spinlock_irqsave, &scx_bypass_lock) /* for the parent bypass check */ scoped_guard(raw_spinlock, &scx_sched_lock) { #ifdef CONFIG_EXT_SUB_SCHED struct scx_sched *parent = scx_parent(sch); if (parent) { s32 ret; /* * Bypass state is spread across per-cpu flags and a * depth count, so inheriting it is tricky and has no * valid use case. Refuse it. */ if (READ_ONCE(parent->bypass_depth)) { scx_error(sch, "parent bypassing (%d)", -EBUSY); return -EBUSY; } ret = rhashtable_lookup_insert_fast(&scx_sched_hash, &sch->hash_node, scx_sched_hash_params); if (ret) { scx_error(sch, "failed to insert into scx_sched_hash (%d)", ret); return ret; } list_add_tail_rcu(&sch->sibling, &parent->children); /* * Pairs with the mb after the ->aborting assertion in * scx_claim_exit(). Either we see ->aborting and back * out, or the exit path sees us and exits us. */ smp_mb(); if (unlikely(READ_ONCE(parent->aborting))) { rhashtable_remove_fast(&scx_sched_hash, &sch->hash_node, scx_sched_hash_params); list_del_rcu(&sch->sibling); scx_error(sch, "parent disabled (%d)", -ENOENT); return -ENOENT; } sch->linked = true; } #endif /* CONFIG_EXT_SUB_SCHED */ list_add_tail_rcu(&sch->all, &scx_sched_all); } refresh_watchdog(); return 0; } void scx_unlink_sched(struct scx_sched *sch) { scoped_guard(raw_spinlock_irq, &scx_sched_lock) { #ifdef CONFIG_EXT_SUB_SCHED if (sch->linked) { rhashtable_remove_fast(&scx_sched_hash, &sch->hash_node, scx_sched_hash_params); list_del_rcu(&sch->sibling); sch->linked = false; } #endif /* CONFIG_EXT_SUB_SCHED */ list_del_rcu(&sch->all); } refresh_watchdog(); } /* * Called to disable future dumps and wait for in-progress one while disabling * @sch. Once @sch becomes empty during disable, there's no point in dumping it. * This prevents calling dump ops on a dead sch. */ void scx_disable_dump(struct scx_sched *sch) { guard(raw_spinlock_irqsave)(&scx_dump_lock); sch->dump_disabled = true; } void scx_log_sched_disable(struct scx_sched *sch) { struct scx_exit_info *ei = sch->exit_info; const char *type = scx_parent(sch) ? "sub-scheduler" : "scheduler"; if (ei->kind >= SCX_EXIT_ERROR) { pr_err("sched_ext: BPF %s \"%s\" disabled (%s)\n", type, sch->ops.name, ei->reason); if (ei->msg[0] != '\0') pr_err("sched_ext: %s: %s\n", sch->ops.name, ei->msg); #ifdef CONFIG_STACKTRACE stack_trace_print(ei->bt, ei->bt_len, 2); #endif } else { pr_info("sched_ext: BPF %s \"%s\" disabled (%s)\n", type, sch->ops.name, ei->reason); } } static void scx_root_disable(struct scx_sched *sch) { struct scx_task_iter sti; struct task_struct *p; bool was_switched_all; int cpu; /* guarantee forward progress and wait for descendants to be disabled */ scx_bypass(sch, true); drain_descendants(sch); switch (scx_set_enable_state(SCX_DISABLING)) { case SCX_DISABLING: WARN_ONCE(true, "sched_ext: duplicate disabling instance?"); break; case SCX_DISABLED: pr_warn("sched_ext: ops error detected without ops (%s)\n", sch->exit_info->msg); WARN_ON_ONCE(scx_set_enable_state(SCX_DISABLED) != SCX_DISABLING); goto done; default: break; } /* * Here, every runnable task is guaranteed to make forward progress and * we can safely use blocking synchronization constructs. Actually * disable ops. */ mutex_lock(&scx_enable_mutex); was_switched_all = scx_switched_all(); static_branch_disable(&__scx_switched_all); WRITE_ONCE(scx_switching_all, false); /* * Shut down cgroup support before tasks so that the cgroup attach and * migration paths don't race against scx_disable_and_exit_task(). */ scx_cgroup_lock(); scx_cgroup_enabled = false; scx_cgroup_exit(sch); scx_cgroup_unlock(); /* * The BPF scheduler is going away. All tasks including %TASK_DEAD ones * must be switched out and exited synchronously. */ percpu_down_write(&scx_fork_rwsem); scx_init_task_enabled = false; scx_task_iter_start(&sti, NULL); while ((p = scx_task_iter_next_locked(&sti))) { unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK; const struct sched_class *old_class = p->sched_class; const struct sched_class *new_class = scx_setscheduler_class(p); update_rq_clock(task_rq(p)); if (old_class != new_class) queue_flags |= DEQUEUE_CLASS; scoped_guard (sched_change, p, queue_flags) { p->sched_class = new_class; } scx_disable_and_exit_task(scx_task_sched(p), p); } scx_task_iter_stop(&sti); scx_disable_dump(sch); scx_cgroup_lock(); set_cgroup_sched(sch_cgroup(sch), NULL); scx_cgroup_unlock(); percpu_up_write(&scx_fork_rwsem); /* * Re-balance the dl_server bandwidth reservations: detach ext_server * (no more sched_ext tasks) and reinstate fair_server if it was * previously detached because we were running in full mode. * * Unlike the enable path, this runs on a recovery path that cannot * fail, so we use dl_server_swap_bw() to atomically free ext_server's * bandwidth and reclaim it for fair_server under the same dl_b lock. * * The swap can still fail with -EBUSY if someone bumped ext_server's * runtime via debugfs between enable and disable; in that narrow case * both servers end up detached and we just WARN. */ for_each_possible_cpu(cpu) { struct rq *rq = cpu_rq(cpu); scoped_guard(rq_lock_irqsave, rq) { update_rq_clock(rq); if (was_switched_all) { if (WARN_ON_ONCE(dl_server_swap_bw(&rq->ext_server, &rq->fair_server))) pr_warn("failed to re-attach fair_server on CPU %d\n", cpu); } else { dl_server_detach_bw(&rq->ext_server); } } } /* no task is on scx, turn off all the switches and flush in-progress calls */ static_branch_disable(&__scx_enabled); static_branch_disable(&__scx_is_cid_type); if (sch->ops.flags & SCX_OPS_TID_TO_TASK) static_branch_disable(&__scx_tid_to_task_enabled); bitmap_zero(sch->has_op, SCX_OPI_END); scx_idle_disable(); synchronize_rcu(); if (sch->ops.flags & SCX_OPS_TID_TO_TASK) rhashtable_free_and_destroy(&scx_tid_hash, NULL, NULL); scx_log_sched_disable(sch); if (sch->ops.exit) SCX_CALL_OP(sch, exit, NULL, sch->exit_info); /* * @sch's non-ops programs such as timers and tracers can fire after * ops.exit(). Now that exit is complete, stop scx_prog_sched() from * resolving to @sch and drain in-flight resolvers. */ WRITE_ONCE(sch->dead, true); synchronize_rcu(); scx_unlink_sched(sch); /* * scx_root clearing and cid table retirement must be inside * cpus_read_lock(). See handle_hotplug(). */ cpus_read_lock(); RCU_INIT_POINTER(scx_root, NULL); scx_cid_retire_tables(); cpus_read_unlock(); /* * Delete the kobject from the hierarchy synchronously. Otherwise, sysfs * could observe an object of the same name still in the hierarchy when * the next scheduler is loaded. */ #ifdef CONFIG_EXT_SUB_SCHED if (sch->sub_kset) kobject_del(&sch->sub_kset->kobj); #endif /* not added if enable failed before scx_sched_sysfs_add() */ if (sch->kobj.state_in_sysfs) kobject_del(&sch->kobj); free_kick_syncs(); mutex_unlock(&scx_enable_mutex); WARN_ON_ONCE(scx_set_enable_state(SCX_DISABLED) != SCX_DISABLING); done: scx_bypass(sch, false); } /** * scx_propagate_exit_irq_workfn - Claim SCX_EXIT_PARENT on the exiting subtree * @irq_work: &scx_sched.propagate_exit_irq_work * * Queued by scx_claim_exit() after a non-PARENT claim. Claims SCX_EXIT_PARENT * on each descendant, giving every one its own disable work - most of disabling * is serialized but ops.exit() can take arbitrarily long and running them in * separate helper kthreads parallelizes it. No recursion as only non-PARENT * claims propagate. */ static void scx_propagate_exit_irq_workfn(struct irq_work *irq_work) { struct scx_sched *sch = container_of(irq_work, struct scx_sched, propagate_exit_irq_work); struct scx_sched *pos; scoped_guard (raw_spinlock_irqsave, &scx_sched_lock) { scx_for_each_descendant_pre(pos, sch) scx_disable(pos, SCX_EXIT_PARENT); } } /* * Claim the exit on @sch. The caller must ensure that the helper kthread work * is kicked before the current task can be preempted. Once exit_kind is * claimed, scx_error() can no longer trigger, so if the current task gets * preempted and the BPF scheduler fails to schedule it back, the helper work * will never be kicked and the whole system can wedge. * * Lock-free and safe to call from any context including NMI. */ static bool scx_claim_exit(struct scx_sched *sch, enum scx_exit_kind kind) { int none = SCX_EXIT_NONE; lockdep_assert_preemption_disabled(); if (WARN_ON_ONCE(kind == SCX_EXIT_NONE || kind == SCX_EXIT_DONE)) kind = SCX_EXIT_ERROR; if (!atomic_try_cmpxchg(&sch->exit_kind, &none, kind)) return false; if (kind == SCX_EXIT_PARENT) { /* an ancestor is already sweeping the subtree */ WRITE_ONCE(sch->aborting, true); } else { struct scx_sched *pos; /* * CPUs may be live-locked in the dispatch paths of @sch or its * descendants, which ->aborting breaks. Sweep the subtree * locklessly so that this works from NMI. smp_store_mb() orders * each node's ->aborting store before its children are walked - * either we see a racing scx_link_sched() on ->children or it * sees ->aborting. */ scoped_guard (rcu) { scx_for_each_descendant_pre(pos, sch) smp_store_mb(pos->aborting, true); } irq_work_queue(&sch->propagate_exit_irq_work); } /* fired after ->aborting is set so callbacks can't delay recovery */ trace_sched_ext_exit(sch, kind); return true; } static void scx_disable_workfn(struct kthread_work *work) { struct scx_sched *sch = container_of(work, struct scx_sched, disable_work); struct scx_exit_info *ei = sch->exit_info; int kind; kind = atomic_read(&sch->exit_kind); while (true) { if (kind == SCX_EXIT_DONE) /* already disabled? */ return; WARN_ON_ONCE(kind == SCX_EXIT_NONE); if (atomic_try_cmpxchg(&sch->exit_kind, &kind, SCX_EXIT_DONE)) break; } ei->kind = kind; ei->reason = scx_exit_reason(ei->kind); if (scx_parent(sch)) scx_sub_disable(sch); else scx_root_disable(sch); } static void scx_disable(struct scx_sched *sch, enum scx_exit_kind kind) { guard(preempt)(); if (scx_claim_exit(sch, kind)) irq_work_queue(&sch->disable_irq_work); } /** * scx_flush_disable_work - flush the disable work and wait for it to finish * @sch: the scheduler * * sch->disable_work might still not queued, causing kthread_flush_work() * as a noop. Syncing the irq_work first is required to guarantee the * kthread work has been queued before waiting for it. */ void scx_flush_disable_work(struct scx_sched *sch) { int kind; do { irq_work_sync(&sch->disable_irq_work); kthread_flush_work(&sch->disable_work); kind = atomic_read(&sch->exit_kind); } while (kind != SCX_EXIT_NONE && kind != SCX_EXIT_DONE); } static void dump_newline(struct seq_buf *s) { trace_sched_ext_dump(""); /* @s may be zero sized and seq_buf triggers WARN if so */ if (s->size) seq_buf_putc(s, '\n'); } __printf(2, 3) void scx_dump_line(struct seq_buf *s, const char *fmt, ...) { va_list args; #ifdef CONFIG_TRACEPOINTS if (trace_sched_ext_dump_enabled()) { /* protected by scx_dump_lock */ static char line_buf[SCX_EXIT_MSG_LEN]; va_start(args, fmt); vscnprintf(line_buf, sizeof(line_buf), fmt, args); va_end(args); trace_call__sched_ext_dump(line_buf); } #endif /* @s may be zero sized and seq_buf triggers WARN if so */ if (s->size) { va_start(args, fmt); seq_buf_vprintf(s, fmt, args); va_end(args); seq_buf_putc(s, '\n'); } } static void dump_stack_trace(struct seq_buf *s, const char *prefix, const unsigned long *bt, unsigned int len) { unsigned int i; for (i = 0; i < len; i++) scx_dump_line(s, "%s%pS", prefix, (void *)bt[i]); } static void ops_dump_init(struct seq_buf *s, const char *prefix) { struct scx_dump_data *dd = &scx_dump_data; lockdep_assert_irqs_disabled(); dd->cpu = smp_processor_id(); /* allow scx_bpf_dump() */ dd->first = true; dd->cursor = 0; dd->s = s; dd->prefix = prefix; } static void ops_dump_flush(void) { struct scx_dump_data *dd = &scx_dump_data; char *line = dd->buf.line; if (!dd->cursor) return; /* * There's something to flush and this is the first line. Insert a blank * line to distinguish ops dump. */ if (dd->first) { dump_newline(dd->s); dd->first = false; } /* * There may be multiple lines in $line. Scan and emit each line * separately. */ while (true) { char *end = line; char c; while (*end != '\n' && *end != '\0') end++; /* * If $line overflowed, it may not have newline at the end. * Always emit with a newline. */ c = *end; *end = '\0'; scx_dump_line(dd->s, "%s%s", dd->prefix, line); if (c == '\0') break; /* move to the next line */ end++; if (*end == '\0') break; line = end; } dd->cursor = 0; } static void ops_dump_exit(void) { ops_dump_flush(); scx_dump_data.cpu = -1; } static void scx_dump_task(struct scx_sched *sch, struct seq_buf *s, struct scx_dump_ctx *dctx, struct rq *rq, struct task_struct *p, char marker) { static unsigned long bt[SCX_EXIT_BT_LEN]; struct scx_sched *task_sch = scx_task_sched(p); const char *own_marker; char sch_id_buf[32]; char dsq_id_buf[19] = "(n/a)"; unsigned long ops_state = atomic_long_read(&p->scx.ops_state); unsigned int bt_len = 0; own_marker = task_sch == sch ? "*" : ""; if (task_sch->level == 0) scnprintf(sch_id_buf, sizeof(sch_id_buf), "root"); else scnprintf(sch_id_buf, sizeof(sch_id_buf), "sub%d-%llu", task_sch->level, task_sch->ops.sub_cgroup_id); if (p->scx.dsq) scnprintf(dsq_id_buf, sizeof(dsq_id_buf), "0x%llx", (unsigned long long)p->scx.dsq->id); dump_newline(s); scx_dump_line(s, " %c%c %s[%d] %s%s %+ldms", marker, task_state_to_char(p), p->comm, p->pid, own_marker, sch_id_buf, jiffies_delta_msecs(p->scx.runnable_at, dctx->at_jiffies)); scx_dump_line(s, " scx_state/flags=%u/0x%x dsq_flags=0x%x ops_state/qseq=%lu/%lu", scx_get_task_state(p) >> SCX_TASK_STATE_SHIFT, p->scx.flags & ~SCX_TASK_STATE_MASK, p->scx.dsq_flags, ops_state & SCX_OPSS_STATE_MASK, ops_state >> SCX_OPSS_QSEQ_SHIFT); scx_dump_line(s, " sticky/holding_cpu=%d/%d dsq_id=%s", p->scx.sticky_cpu, p->scx.holding_cpu, dsq_id_buf); scx_dump_line(s, " dsq_vtime=%llu slice=%llu weight=%u", p->scx.dsq_vtime, p->scx.slice, p->scx.weight); scx_dump_line(s, " cpus=%*pb no_mig=%u", cpumask_pr_args(p->cpus_ptr), p->migration_disabled); if (SCX_HAS_OP(sch, dump_task)) { ops_dump_init(s, " "); SCX_CALL_OP(sch, dump_task, rq, dctx, p); ops_dump_exit(); } #ifdef CONFIG_STACKTRACE bt_len = stack_trace_save_tsk(p, bt, SCX_EXIT_BT_LEN, 1); #endif if (bt_len) { dump_newline(s); dump_stack_trace(s, " ", bt, bt_len); } } static void scx_dump_cpu(struct scx_sched *sch, struct seq_buf *s, struct scx_dump_ctx *dctx, int cpu, bool dump_all_tasks) { struct rq *rq = cpu_rq(cpu); struct scx_sched_pcpu *pcpu = per_cpu_ptr(sch->pcpu, cpu); struct rq_flags rf; struct task_struct *p; struct seq_buf ns; size_t avail, used; char *buf; bool idle; rq_lock_irqsave(rq, &rf); idle = list_empty(&rq->scx.runnable_list) && rq->curr->sched_class == &idle_sched_class; if (idle && !SCX_HAS_OP(sch, dump_cpu)) goto next; /* * We don't yet know whether ops.dump_cpu() will produce output * and we may want to skip the default CPU dump if it doesn't. * Use a nested seq_buf to generate the standard dump so that we * can decide whether to commit later. */ avail = seq_buf_get_buf(s, &buf); seq_buf_init(&ns, buf, avail); dump_newline(&ns); scx_dump_line(&ns, "CPU %-4d: nr_run=%u flags=0x%x cpu_rel=%d ops_qseq=%lu ksync=%lu", cpu, rq->scx.nr_running, rq->scx.flags, rq->scx.cpu_released, rq->scx.ops_qseq, rq->scx.kick_sync); scx_rescue_dump(&ns, rq); scx_dump_line(&ns, " curr=%s[%d] class=%ps", rq->curr->comm, rq->curr->pid, rq->curr->sched_class); if (!cpumask_empty(pcpu->cpus_to_kick)) scx_dump_line(&ns, " cpus_to_kick : %*pb", cpumask_pr_args(pcpu->cpus_to_kick)); if (!cpumask_empty(pcpu->cpus_to_kick_if_idle)) scx_dump_line(&ns, " idle_to_kick : %*pb", cpumask_pr_args(pcpu->cpus_to_kick_if_idle)); if (!cpumask_empty(pcpu->cpus_to_preempt)) scx_dump_line(&ns, " cpus_to_preempt: %*pb", cpumask_pr_args(pcpu->cpus_to_preempt)); if (!cpumask_empty(pcpu->cpus_to_wait)) scx_dump_line(&ns, " cpus_to_wait : %*pb", cpumask_pr_args(pcpu->cpus_to_wait)); if (!cpumask_empty(rq->scx.cpus_to_sync)) scx_dump_line(&ns, " cpus_to_sync : %*pb", cpumask_pr_args(rq->scx.cpus_to_sync)); used = seq_buf_used(&ns); if (SCX_HAS_OP(sch, dump_cpu)) { ops_dump_init(&ns, " "); SCX_CALL_OP(sch, dump_cpu, rq, dctx, scx_cpu_arg(cpu), idle); ops_dump_exit(); } /* * If idle && nothing generated by ops.dump_cpu(), there's * nothing interesting. Skip. */ if (idle && used == seq_buf_used(&ns)) goto next; /* * $s may already have overflowed when $ns was created. If so, * calling commit on it will trigger BUG. */ if (avail) { seq_buf_commit(s, seq_buf_used(&ns)); if (seq_buf_has_overflowed(&ns)) seq_buf_set_overflow(s); } if (rq->curr->sched_class == &ext_sched_class && (dump_all_tasks || scx_task_on_sched(sch, rq->curr))) scx_dump_task(sch, s, dctx, rq, rq->curr, '*'); list_for_each_entry(p, &rq->scx.runnable_list, scx.runnable_node) if (dump_all_tasks || scx_task_on_sched(sch, p)) scx_dump_task(sch, s, dctx, rq, p, ' '); next: rq_unlock_irqrestore(rq, &rf); } /* * Dump scheduler state. If @dump_all_tasks is true, dump all tasks regardless * of which scheduler they belong to. If false, only dump tasks owned by @sch. * For SysRq-D dumps, @dump_all_tasks=false since all schedulers are dumped * separately. For error dumps, @dump_all_tasks=true since only the failing * scheduler is dumped. */ static void scx_dump_state(struct scx_sched *sch, struct scx_exit_info *ei, size_t dump_len, bool dump_all_tasks) { static const char trunc_marker[] = "\n\n~~~~ TRUNCATED ~~~~\n"; struct scx_dump_ctx dctx = { .kind = ei->kind, .exit_code = ei->exit_code, .reason = ei->reason, .at_ns = ktime_get_ns(), .at_jiffies = jiffies, }; struct seq_buf s; struct scx_event_stats events; int cpu; guard(raw_spinlock_irqsave)(&scx_dump_lock); if (sch->dump_disabled) return; seq_buf_init(&s, ei->dump, dump_len); #ifdef CONFIG_EXT_SUB_SCHED if (sch->level == 0) scx_dump_line(&s, "%s: root", sch->ops.name); else scx_dump_line(&s, "%s: sub%d-%llu %s", sch->ops.name, sch->level, sch->ops.sub_cgroup_id, sch->cgrp_path); #endif if (ei->kind == SCX_EXIT_NONE) { scx_dump_line(&s, "Debug dump triggered by %s", ei->reason); } else { if (ei->exit_cpu >= 0) scx_dump_line(&s, "%s[%d] triggered exit kind %d on CPU %d:", current->comm, current->pid, ei->kind, ei->exit_cpu); else scx_dump_line(&s, "%s[%d] triggered exit kind %d:", current->comm, current->pid, ei->kind); scx_dump_line(&s, " %s (%s)", ei->reason, ei->msg); dump_newline(&s); scx_dump_line(&s, "Backtrace:"); dump_stack_trace(&s, " ", ei->bt, ei->bt_len); } if (SCX_HAS_OP(sch, dump)) { ops_dump_init(&s, ""); SCX_CALL_OP(sch, dump, NULL, &dctx); ops_dump_exit(); } dump_newline(&s); scx_dump_line(&s, "CPU states"); scx_dump_line(&s, "----------"); /* * Dump stalled CPUs first so they aren't lost to dump truncation, then * walk the rest in order. Fall back to exit_cpu if no stall mask set. */ if (!cpumask_empty(sch->stall_cpus)) { for_each_cpu(cpu, sch->stall_cpus) scx_dump_cpu(sch, &s, &dctx, cpu, dump_all_tasks); for_each_possible_cpu(cpu) { if (!cpumask_test_cpu(cpu, sch->stall_cpus)) scx_dump_cpu(sch, &s, &dctx, cpu, dump_all_tasks); } } else { if (ei->exit_cpu >= 0) scx_dump_cpu(sch, &s, &dctx, ei->exit_cpu, dump_all_tasks); for_each_possible_cpu(cpu) { if (cpu != ei->exit_cpu) scx_dump_cpu(sch, &s, &dctx, cpu, dump_all_tasks); } } dump_newline(&s); scx_dump_line(&s, "Event counters"); scx_dump_line(&s, "--------------"); scx_read_events(sch, &events); #define SCX_EVENT(name) scx_dump_event(s, &events, name) SCX_EVENTS_LIST(SCX_EVENT); #undef SCX_EVENT if (seq_buf_has_overflowed(&s) && dump_len >= sizeof(trunc_marker)) memcpy(ei->dump + dump_len - sizeof(trunc_marker), trunc_marker, sizeof(trunc_marker)); } static void scx_disable_irq_workfn(struct irq_work *irq_work) { struct scx_sched *sch = container_of(irq_work, struct scx_sched, disable_irq_work); struct scx_exit_info *ei = sch->exit_info; if (ei->kind >= SCX_EXIT_ERROR) scx_dump_state(sch, ei, sch->ops.exit_dump_len, true); kthread_queue_work(sch->helper, &sch->disable_work); } /* finish exit_info and kick the disable work, ei->msg must already be set */ static void scx_finish_exit(struct scx_sched *sch, enum scx_exit_kind kind, s64 exit_code, s32 exit_cpu) { struct scx_exit_info *ei = sch->exit_info; ei->exit_code = exit_code; #ifdef CONFIG_STACKTRACE /* * stack_trace_save()'s NMI-safety is arch-dependent and undocumented. * Skip the backtrace when exiting from NMI. */ if (kind >= SCX_EXIT_ERROR && !in_nmi()) ei->bt_len = stack_trace_save(ei->bt, SCX_EXIT_BT_LEN, 1); #endif /* * Set ei->kind and ->reason for scx_dump_state(). They'll be set again * in scx_disable_workfn(). */ ei->kind = kind; ei->reason = scx_exit_reason(ei->kind); ei->exit_cpu = exit_cpu; irq_work_queue(&sch->disable_irq_work); } bool scx_vexit(struct scx_sched *sch, enum scx_exit_kind kind, s64 exit_code, s32 exit_cpu, const char *fmt, va_list args) { struct scx_exit_info *ei = sch->exit_info; guard(preempt)(); if (!scx_claim_exit(sch, kind)) return false; vscnprintf(ei->msg, SCX_EXIT_MSG_LEN, fmt, args); scx_finish_exit(sch, kind, exit_code, exit_cpu); return true; } static int alloc_kick_syncs(void) { int cpu; /* * Allocate per-CPU arrays sized by nr_cpu_ids. Use kvzalloc as size * can exceed percpu allocator limits on large machines. */ for_each_possible_cpu(cpu) { struct scx_kick_syncs __rcu **ksyncs = per_cpu_ptr(&scx_kick_syncs, cpu); struct scx_kick_syncs *new_ksyncs; WARN_ON_ONCE(rcu_access_pointer(*ksyncs)); new_ksyncs = kvzalloc_node(struct_size(new_ksyncs, syncs, nr_cpu_ids), GFP_KERNEL, cpu_to_node(cpu)); if (!new_ksyncs) { free_kick_syncs(); return -ENOMEM; } rcu_assign_pointer(*ksyncs, new_ksyncs); } return 0; } static void free_pnode(struct scx_sched_pnode *pnode) { if (!pnode) return; exit_dsq(&pnode->global_dsq); kfree(pnode); } static struct scx_sched_pnode *alloc_pnode(struct scx_sched *sch, int node) { struct scx_sched_pnode *pnode; pnode = kzalloc_node(sizeof(*pnode), GFP_KERNEL, node); if (!pnode) return NULL; if (scx_init_dsq(&pnode->global_dsq, SCX_DSQ_GLOBAL, sch)) { kfree(pnode); return NULL; } return pnode; } /* * Allocate and initialize a new scx_sched. @cgrp's reference is always * consumed whether the function succeeds or fails. */ struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd, struct cgroup *cgrp, struct scx_sched *parent) { struct sched_ext_ops *ops = cmd->ops; struct scx_sched *sch; s32 level = parent ? parent->level + 1 : 0; s32 node, cpu, ret, bypass_fail_cpu = nr_cpu_ids; sch = kzalloc_flex(*sch, ancestors, level + 1); if (!sch) { ret = -ENOMEM; goto err_put_cgrp; } sch->exit_info = alloc_exit_info(ops->exit_dump_len); if (!sch->exit_info) { ret = -ENOMEM; goto err_free_sch; } ret = rhashtable_init(&sch->dsq_hash, &dsq_hash_params); if (ret < 0) goto err_free_ei; sch->pnode = kzalloc_objs(sch->pnode[0], nr_node_ids); if (!sch->pnode) { ret = -ENOMEM; goto err_free_hash; } for_each_node_state(node, N_POSSIBLE) { sch->pnode[node] = alloc_pnode(sch, node); if (!sch->pnode[node]) { ret = -ENOMEM; goto err_free_pnode; } } sch->dsp_max_batch = ops->dispatch_max_batch ?: SCX_DSP_DFL_MAX_BATCH; sch->pcpu = __alloc_percpu(struct_size_t(struct scx_sched_pcpu, dsp_ctx.buf, sch->dsp_max_batch), __alignof__(struct scx_sched_pcpu)); if (!sch->pcpu) { ret = -ENOMEM; goto err_free_pnode; } for_each_possible_cpu(cpu) { ret = scx_init_dsq(scx_bypass_dsq(sch, cpu), SCX_DSQ_BYPASS, sch); if (ret) { bypass_fail_cpu = cpu; goto err_free_pcpu; } } for_each_possible_cpu(cpu) { struct scx_sched_pcpu *pcpu = per_cpu_ptr(sch->pcpu, cpu); node = cpu_to_node(cpu); pcpu->sch = sch; INIT_LIST_HEAD(&pcpu->deferred_reenq_local.node); #ifdef CONFIG_EXT_SUB_SCHED init_llist_node(&pcpu->ecaps_to_sync_node); #endif INIT_LIST_HEAD(&pcpu->to_kick_node); if (!zalloc_cpumask_var_node(&pcpu->cpus_to_kick, GFP_KERNEL, node) || !zalloc_cpumask_var_node(&pcpu->cpus_to_kick_if_idle, GFP_KERNEL, node) || !zalloc_cpumask_var_node(&pcpu->cpus_to_preempt, GFP_KERNEL, node) || !zalloc_cpumask_var_node(&pcpu->cpus_to_wait, GFP_KERNEL, node)) { ret = -ENOMEM; goto err_free_pcpu; } } sch->helper = kthread_run_worker(0, "sched_ext_helper"); if (IS_ERR(sch->helper)) { ret = PTR_ERR(sch->helper); goto err_free_pcpu; } sched_set_fifo(sch->helper->task); if (parent) memcpy(sch->ancestors, parent->ancestors, level * sizeof(parent->ancestors[0])); sch->ancestors[level] = sch; sch->level = level; sch->id = atomic64_inc_return(&scx_sched_id_cursor); if (ops->timeout_ms) sch->watchdog_timeout = msecs_to_jiffies(ops->timeout_ms); else sch->watchdog_timeout = SCX_WATCHDOG_MAX_TIMEOUT; sch->slice_dfl = SCX_SLICE_DFL; atomic_set(&sch->exit_kind, SCX_EXIT_NONE); sch->disable_irq_work = IRQ_WORK_INIT_HARD(scx_disable_irq_workfn); sch->propagate_exit_irq_work = IRQ_WORK_INIT_HARD(scx_propagate_exit_irq_workfn); kthread_init_work(&sch->disable_work, scx_disable_workfn); timer_setup(&sch->bypass_lb_timer, scx_bypass_lb_timerfn, 0); if (!alloc_cpumask_var(&sch->bypass_lb_donee_cpumask, GFP_KERNEL)) { ret = -ENOMEM; goto err_stop_helper; } if (!alloc_cpumask_var(&sch->bypass_lb_resched_cpumask, GFP_KERNEL)) { ret = -ENOMEM; goto err_free_lb_cpumask; } if (!zalloc_cpumask_var(&sch->stall_cpus, GFP_KERNEL)) { ret = -ENOMEM; goto err_free_lb_resched_cpumask; } /* * Copy ops through the right union view. For cid-form the source is * struct sched_ext_ops_cid which lacks the trailing cpu_acquire/ * cpu_release; those stay zero from kzalloc. */ if (cmd->is_cid_type) { sch->ops_cid = *cmd->ops_cid; sch->is_cid_type = true; } else { sch->ops = *cmd->ops; } #ifdef CONFIG_EXT_SUB_SCHED char *buf = kzalloc(PATH_MAX, GFP_KERNEL); if (!buf) { ret = -ENOMEM; goto err_free_lb_resched; } cgroup_path(cgrp, buf, PATH_MAX); sch->cgrp_path = kstrdup(buf, GFP_KERNEL); kfree(buf); if (!sch->cgrp_path) { ret = -ENOMEM; goto err_free_lb_resched; } sch->cgrp = cgrp; INIT_LIST_HEAD(&sch->children); INIT_LIST_HEAD(&sch->sibling); #endif /* CONFIG_EXT_SUB_SCHED */ /* * Publishing makes @sch visible to scx_prog_sched() readers. Failure * paths after this point must free @sch through kobject_put() whose * release path defers the actual freeing by an RCU grace period. */ rcu_assign_pointer(ops->priv, sch); sch->kobj.kset = scx_kset; INIT_LIST_HEAD(&sch->all); #ifdef CONFIG_EXT_SUB_SCHED if (parent) { /* * Pin @parent for @sch's lifetime. The kobject hierarchy pins * it only via @parent->sub_kset, which is dropped during * disable. Released in scx_sched_free_rcu_work(). */ kobject_get(&parent->kobj); } #endif /* CONFIG_EXT_SUB_SCHED */ /* * Init the kobj but don't add to sysfs yet. The enable path calls * scx_sched_sysfs_add() once @sch's sysfs-visible state is initialized. */ kobject_init(&sch->kobj, &scx_ktype); /* * Consume the arena_map ref bpf_scx_reg_cid() took. Defer to here so * earlier failure paths leave cmd->arena_map set and bpf_scx_reg_cid * drops the ref. After this point, sch owns the ref and any cleanup * runs through scx_sched_free_rcu_work() which puts it. */ sch->arena_map = cmd->arena_map; /* BPF arena is only available on MMU && 64BIT */ #if defined(CONFIG_MMU) && defined(CONFIG_64BIT) if (sch->arena_map) sch->arena_kern_base = bpf_arena_map_kern_vm_start(sch->arena_map); #endif cmd->arena_map = NULL; return sch; #ifdef CONFIG_EXT_SUB_SCHED err_free_lb_resched: free_cpumask_var(sch->stall_cpus); #endif err_free_lb_resched_cpumask: free_cpumask_var(sch->bypass_lb_resched_cpumask); err_free_lb_cpumask: free_cpumask_var(sch->bypass_lb_donee_cpumask); err_stop_helper: kthread_destroy_worker(sch->helper); err_free_pcpu: for_each_possible_cpu(cpu) { struct scx_sched_pcpu *pcpu = per_cpu_ptr(sch->pcpu, cpu); free_cpumask_var(pcpu->cpus_to_kick); free_cpumask_var(pcpu->cpus_to_kick_if_idle); free_cpumask_var(pcpu->cpus_to_preempt); free_cpumask_var(pcpu->cpus_to_wait); } for_each_possible_cpu(cpu) { if (cpu == bypass_fail_cpu) break; exit_dsq(scx_bypass_dsq(sch, cpu)); } free_percpu(sch->pcpu); err_free_pnode: for_each_node_state(node, N_POSSIBLE) free_pnode(sch->pnode[node]); kfree(sch->pnode); err_free_hash: rhashtable_free_and_destroy(&sch->dsq_hash, NULL, NULL); err_free_ei: free_exit_info(sch->exit_info); err_free_sch: kfree(sch); err_put_cgrp: #ifdef CONFIG_EXT_SUB_SCHED cgroup_put(cgrp); #endif return ERR_PTR(ret); } /* * Add @sch's kobject to sysfs, and create its sub_kset if the scheduler * implements ops.sub_attach. Called by the enable workfns once @sch's * sysfs-visible state is initialized. */ int scx_sched_sysfs_add(struct scx_sched *sch) { #ifdef CONFIG_EXT_SUB_SCHED struct scx_sched *parent = scx_parent(sch); int ret; if (parent) ret = kobject_add(&sch->kobj, &parent->sub_kset->kobj, "sub-%llu", cgroup_id(sch_cgroup(sch))); else ret = kobject_add(&sch->kobj, NULL, "root"); if (ret < 0) return ret; if (sch->ops.sub_attach) { sch->sub_kset = kset_create_and_add("sub", NULL, &sch->kobj); if (!sch->sub_kset) return -ENOMEM; } return 0; #else return kobject_add(&sch->kobj, NULL, "root"); #endif } static int check_hotplug_seq(struct scx_sched *sch, const struct sched_ext_ops *ops) { unsigned long long global_hotplug_seq; /* * If a hotplug event has occurred between when a scheduler was * initialized, and when we were able to attach, exit and notify user * space about it. */ if (ops->hotplug_seq) { global_hotplug_seq = atomic_long_read(&scx_hotplug_seq); if (ops->hotplug_seq != global_hotplug_seq) { scx_exit(sch, SCX_EXIT_UNREG_KERN, SCX_ECODE_ACT_RESTART | SCX_ECODE_RSN_HOTPLUG, "expected hotplug seq %llu did not match actual %llu", ops->hotplug_seq, global_hotplug_seq); return -EBUSY; } } return 0; } int scx_validate_ops(struct scx_sched *sch, const struct sched_ext_ops *ops) { /* * It doesn't make sense to specify the SCX_OPS_ENQ_LAST flag if the * ops.enqueue() callback isn't implemented. */ if ((ops->flags & SCX_OPS_ENQ_LAST) && !ops->enqueue) { scx_error(sch, "SCX_OPS_ENQ_LAST requires ops.enqueue() to be implemented"); return -EINVAL; } /* * SCX_OPS_TID_TO_TASK is enabled by the root scheduler. A sub-sched * may set it to declare a dependency; reject if the root hasn't * enabled it. */ if ((ops->flags & SCX_OPS_TID_TO_TASK) && scx_parent(sch) && !(sch->ancestors[0]->ops.flags & SCX_OPS_TID_TO_TASK)) { scx_error(sch, "SCX_OPS_TID_TO_TASK requires root scheduler to enable it"); return -EINVAL; } /* * SCX_OPS_BUILTIN_IDLE_PER_NODE requires built-in CPU idle * selection policy to be enabled. */ if ((ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE) && (ops->update_idle && !(ops->flags & SCX_OPS_KEEP_BUILTIN_IDLE))) { scx_error(sch, "SCX_OPS_BUILTIN_IDLE_PER_NODE requires CPU idle selection enabled"); return -EINVAL; } /* * cid-form's struct is shorter and doesn't include the cpu_acquire / * cpu_release tail; reading those fields off a cid-form @ops would * run past the BPF allocation. Skip for cid-form. */ if (!sch->is_cid_type && (ops->cpu_acquire || ops->cpu_release)) pr_warn_ratelimited("ops->cpu_acquire/release() are deprecated, use sched_switch TP instead\n"); /* * Sub-scheduler support is tied to the cid-form struct_ops. A sub-sched * attaches through a cid-form-only interface (sub_attach/sub_detach), * and a root that accepts sub-scheds must expose cid-form state to * them. Reject cpu-form schedulers on either side. */ if (!sch->is_cid_type) { if (scx_parent(sch)) { scx_error(sch, "sub-sched requires cid-form struct_ops"); return -EINVAL; } if (ops->sub_attach || ops->sub_detach) { scx_error(sch, "sub_attach/sub_detach requires cid-form struct_ops"); return -EINVAL; } } return 0; } static void scx_root_enable_workfn(struct kthread_work *work) { struct scx_enable_cmd *cmd = container_of(work, struct scx_enable_cmd, work); struct sched_ext_ops *ops = cmd->ops; struct cgroup *cgrp = root_cgroup(); struct scx_sched *sch; struct scx_task_iter sti; struct task_struct *p; int i, cpu, ret; mutex_lock(&scx_enable_mutex); if (scx_enable_state() != SCX_DISABLED) { ret = -EBUSY; goto err_unlock; } /* * @ops->priv binds @ops to its scx_sched instance. It is set here by * scx_alloc_and_add_sched() and cleared at the tail of bpf_scx_unreg(), * which runs after scx_root_disable() has dropped scx_enable_mutex. If * it's still non-NULL here, a previous attachment on @ops has not * finished tearing down; proceeding would let the in-flight unreg's * RCU_INIT_POINTER(NULL) clobber the @ops->priv we are about to assign. */ if (rcu_access_pointer(ops->priv)) { ret = -EBUSY; goto err_unlock; } ret = alloc_kick_syncs(); if (ret) goto err_unlock; if (ops->flags & SCX_OPS_TID_TO_TASK) { ret = rhashtable_init(&scx_tid_hash, &scx_tid_hash_params); if (ret) goto err_free_ksyncs; } #ifdef CONFIG_EXT_SUB_SCHED cgroup_get(cgrp); #endif sch = scx_alloc_and_add_sched(cmd, cgrp, NULL); if (IS_ERR(sch)) { ret = PTR_ERR(sch); goto err_free_tid_hash; } if (sch->is_cid_type) static_branch_enable(&__scx_is_cid_type); /* * Transition to ENABLING and clear exit info to arm the disable path. * Failure triggers full disabling from here on. */ WARN_ON_ONCE(scx_set_enable_state(SCX_ENABLING) != SCX_DISABLED); WARN_ON_ONCE(scx_root); atomic_long_set(&scx_nr_rejected, 0); for_each_possible_cpu(cpu) { struct rq *rq = cpu_rq(cpu); rq->scx.local_dsq.sched = sch; rq->scx.cpuperf_target = SCX_CPUPERF_ONE; } scx_discard_stale_ecaps_syncs(); scx_rescue_set_knobs(sch); /* * Keep CPUs stable during enable so that the BPF scheduler can track * online CPUs by watching ->on/offline_cpu() after ->init(). */ cpus_read_lock(); /* * Build the cid mapping into a private under-construction set. It * becomes visible to readers only through scx_cid_publish_tables() once * ops.init_cids() has finalized the layout. */ ret = scx_cid_init(sch); if (ret) { cpus_read_unlock(); goto err_disable; } /* * Make the scheduler instance visible. Must be inside cpus_read_lock(). * See handle_hotplug(). */ rcu_assign_pointer(scx_root, sch); ret = scx_link_sched(sch); if (ret) { cpus_read_unlock(); goto err_disable; } scx_idle_enable(ops); /* * A cid-form scheduler finalizes its cid layout in ops.init_cids(), * which may call scx_bpf_cid_override(). Run it before the caps and * shard state are built so the final layout is in effect. */ if (sch->is_cid_type && sch->ops_cid.init_cids) { ret = SCX_CALL_OP_RET(sch, init_cids, NULL); if (ret) { ret = scx_ops_sanitize_err(sch, "init_cids", ret); cpus_read_unlock(); scx_error(sch, "ops.init_cids() failed (%d)", ret); goto err_disable; } } /* the cid layout is final, expose it to readers */ scx_cid_publish_tables(); ret = scx_arena_pool_init(sch); if (ret) { cpus_read_unlock(); goto err_disable; } ret = scx_set_cmask_scratch_alloc(sch); if (ret) { cpus_read_unlock(); goto err_disable; } ret = scx_alloc_pshards(sch); if (ret) { cpus_read_unlock(); goto err_disable; } scx_init_root_caps(sch); /* the cid caps and shards are live now, so ops.init() can query them */ if (sch->ops.init) { ret = SCX_CALL_OP_RET(sch, init, NULL); if (ret) { ret = scx_ops_sanitize_err(sch, "init", ret); cpus_read_unlock(); scx_error(sch, "ops.init() failed (%d)", ret); goto err_disable; } sch->exit_info->flags |= SCX_EFLAG_INITIALIZED; } ret = scx_sched_sysfs_add(sch); if (ret) { cpus_read_unlock(); goto err_disable; } for (i = SCX_OPI_CPU_HOTPLUG_BEGIN; i < SCX_OPI_CPU_HOTPLUG_END; i++) if (((void (**)(void))ops)[i]) set_bit(i, sch->has_op); ret = check_hotplug_seq(sch, ops); if (ret) { cpus_read_unlock(); goto err_disable; } scx_idle_update_selcpu_topology(ops); cpus_read_unlock(); ret = scx_validate_ops(sch, ops); if (ret) goto err_disable; /* * Attach the ext_server bandwidth reservation before anything is * committed so that we can fail the enable if the root domain cannot * accommodate it. The matching fair_server detach is deferred to the * tail of this function, after the switch is fully committed and can no * longer fail. * * On failure, err_disable funnels into scx_root_disable() which * detaches ext_server, so partially-attached state is cleaned up * automatically. */ for_each_possible_cpu(cpu) { struct rq *rq = cpu_rq(cpu); scoped_guard(rq_lock_irqsave, rq) { update_rq_clock(rq); ret = dl_server_attach_bw(&rq->ext_server); } if (ret) { pr_warn("sched_ext: failed to attach ext_server on CPU %d (%d)\n", cpu, ret); goto err_disable; } } /* * Once __scx_enabled is set, %current can be switched to SCX anytime. * This can lead to stalls as some BPF schedulers (e.g. userspace * scheduling) may not function correctly before all tasks are switched. * Init in bypass mode to guarantee forward progress. */ scx_bypass(sch, true); for (i = SCX_OPI_NORMAL_BEGIN; i < SCX_OPI_NORMAL_END; i++) if (((void (**)(void))ops)[i]) set_bit(i, sch->has_op); if (sch->ops.cpu_acquire || sch->ops.cpu_release) sch->ops.flags |= SCX_OPS_HAS_CPU_PREEMPT; /* * Lock out forks, cgroup on/offlining and moves before opening the * floodgate so that they don't wander into the operations prematurely. */ percpu_down_write(&scx_fork_rwsem); WARN_ON_ONCE(scx_init_task_enabled); scx_init_task_enabled = true; /* flip under fork_rwsem; the iter below covers existing tasks */ if (ops->flags & SCX_OPS_TID_TO_TASK) static_branch_enable(&__scx_tid_to_task_enabled); /* * Enable ops for every task. Fork is excluded by scx_fork_rwsem * preventing new tasks from being added. No need to exclude tasks * leaving as sched_ext_free() can handle both prepped and enabled * tasks. Prep all tasks first and then enable them with preemption * disabled. * * All cgroups should be initialized before scx_init_task() so that the * BPF scheduler can reliably track each task's cgroup membership from * scx_init_task(). Lock out cgroup on/offlining and task migrations * while tasks are being initialized so that scx_cgroup_can_attach() * never sees uninitialized tasks. */ scx_cgroup_lock(); set_cgroup_sched(sch_cgroup(sch), sch); ret = scx_cgroup_init(sch); if (ret) goto err_disable_unlock_all; WARN_ON_ONCE(scx_cgroup_enabled); scx_cgroup_enabled = true; scx_task_iter_start(&sti, NULL); while ((p = scx_task_iter_next_locked(&sti))) { /* * @p is in scx_tasks under scx_tasks_lock, and SCX_TASK_DEAD * tasks are filtered by scx_task_iter_next_locked(). * sched_ext_dead() removes @p from scx_tasks under the same * lock before put_task_struct_rcu_user() runs, so @p->usage * is guaranteed > 0 here. */ get_task_struct(p); /* * Set %INIT_BEGIN under the iter's rq lock so that a concurrent * sched_ext_dead() does not call ops.exit_task() on @p while * ops.init_task() is running. If sched_ext_dead() runs before * this store, it has already removed @p from scx_tasks and the * iter won't visit @p; if it runs after, it observes * %INIT_BEGIN and transitions to %DEAD without calling ops, * leaving the post-init recheck below to unwind. */ scx_set_task_state(p, SCX_TASK_INIT_BEGIN); scx_task_iter_unlock(&sti); ret = __scx_init_task(sch, p, NULL, false); scx_task_iter_relock(&sti, p); if (unlikely(ret)) { if (scx_get_task_state(p) != SCX_TASK_DEAD) scx_set_task_state(p, SCX_TASK_NONE); scx_task_iter_stop(&sti); scx_error(sch, "ops.init_task() failed (%d) for %s[%d]", ret, p->comm, p->pid); put_task_struct(p); goto err_disable_unlock_all; } if (scx_get_task_state(p) == SCX_TASK_DEAD) { /* * sched_ext_dead() observed %INIT_BEGIN and set %DEAD. * ops.exit_task() is owed to the sched __scx_init_task() * ran against; call it now. */ scx_sub_init_cancel_task(sch, p); } else { scx_set_task_state(p, SCX_TASK_INIT); scx_set_task_sched(p, sch); scx_set_task_state(p, SCX_TASK_READY); } /* * Insert into the tid hash. scx_tasks_lock is held by the iter; * list_empty() guards against sched_ext_dead() having taken @p * off the list while init ran unlocked. */ if (scx_tid_to_task_enabled() && !list_empty(&p->scx.tasks_node)) scx_tid_hash_insert(p); put_task_struct(p); } scx_task_iter_stop(&sti); scx_cgroup_unlock(); percpu_up_write(&scx_fork_rwsem); /* * All tasks are READY. It's safe to turn on scx_enabled() and switch * all eligible tasks. */ WRITE_ONCE(scx_switching_all, !(ops->flags & SCX_OPS_SWITCH_PARTIAL)); static_branch_enable(&__scx_enabled); /* * We're fully committed and can't fail. The task READY -> ENABLED * transitions here are synchronized against sched_ext_free() through * scx_tasks_lock. */ percpu_down_write(&scx_fork_rwsem); scx_task_iter_start(&sti, NULL); while ((p = scx_task_iter_next_locked(&sti))) { unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE; const struct sched_class *old_class = p->sched_class; const struct sched_class *new_class = scx_setscheduler_class(p); if (scx_get_task_state(p) != SCX_TASK_READY) continue; if (old_class != new_class) queue_flags |= DEQUEUE_CLASS; scoped_guard (sched_change, p, queue_flags) { scx_set_task_slice(p, READ_ONCE(sch->slice_dfl)); p->sched_class = new_class; } } scx_task_iter_stop(&sti); percpu_up_write(&scx_fork_rwsem); scx_bypass(sch, false); if (!scx_tryset_enable_state(SCX_ENABLED, SCX_ENABLING)) { WARN_ON_ONCE(atomic_read(&sch->exit_kind) == SCX_EXIT_NONE); ret = -EBUSY; goto err_disable; } if (!(ops->flags & SCX_OPS_SWITCH_PARTIAL)) static_branch_enable(&__scx_switched_all); /* * Detach the fair_server bandwidth reservation now that the switch * is fully committed. In full mode (!SCX_OPS_SWITCH_PARTIAL) no * task will ever run in the fair class, so give that bandwidth * back to the RT class. The matching ext_server attach already * happened earlier; this only releases bandwidth and cannot fail. * * In partial mode keep fair_server attached. */ if (scx_switched_all()) { for_each_possible_cpu(cpu) { struct rq *rq = cpu_rq(cpu); guard(rq_lock_irqsave)(rq); update_rq_clock(rq); dl_server_detach_bw(&rq->fair_server); } } pr_info("sched_ext: BPF scheduler \"%s\" enabled%s\n", sch->ops.name, scx_switched_all() ? "" : " (partial)"); kobject_uevent(&sch->kobj, KOBJ_ADD); mutex_unlock(&scx_enable_mutex); atomic_long_inc(&scx_enable_seq); cmd->ret = 0; return; err_free_tid_hash: if (ops->flags & SCX_OPS_TID_TO_TASK) rhashtable_free_and_destroy(&scx_tid_hash, NULL, NULL); err_free_ksyncs: free_kick_syncs(); err_unlock: mutex_unlock(&scx_enable_mutex); cmd->ret = ret; return; err_disable_unlock_all: scx_cgroup_unlock(); percpu_up_write(&scx_fork_rwsem); /* we'll soon enter disable path, keep bypass on */ err_disable: mutex_unlock(&scx_enable_mutex); /* * Returning an error code here would not pass all the error information * to userspace. Record errno using scx_error() for cases scx_error() * wasn't already invoked and exit indicating success so that the error * is notified through ops.exit() with all the details. * * Flush scx_disable_work to ensure that error is reported before init * completion. sch's base reference will be put by bpf_scx_unreg(). */ scx_error(sch, "scx_root_enable() failed (%d)", ret); scx_flush_disable_work(sch); cmd->ret = 0; } static s32 scx_enable(struct scx_enable_cmd *cmd, struct bpf_link *link) { static struct kthread_worker *helper; static DEFINE_MUTEX(helper_mutex); if (housekeeping_enabled(HK_TYPE_DOMAIN_BOOT)) { pr_err("sched_ext: Not compatible with \"isolcpus=\" domain isolation\n"); return -EINVAL; } if (!READ_ONCE(helper)) { mutex_lock(&helper_mutex); if (!helper) { struct kthread_worker *w = kthread_run_worker(0, "scx_enable_helper"); if (IS_ERR_OR_NULL(w)) { mutex_unlock(&helper_mutex); return -ENOMEM; } sched_set_fifo(w->task); WRITE_ONCE(helper, w); } mutex_unlock(&helper_mutex); } #ifdef CONFIG_EXT_SUB_SCHED if (cmd->ops->sub_cgroup_id > 1) kthread_init_work(&cmd->work, scx_sub_enable_workfn); else #endif /* CONFIG_EXT_SUB_SCHED */ kthread_init_work(&cmd->work, scx_root_enable_workfn); kthread_queue_work(READ_ONCE(helper), &cmd->work); kthread_flush_work(&cmd->work); return cmd->ret; } /******************************************************************************** * bpf_struct_ops plumbing. */ #include #include #include static const struct btf_type *task_struct_type; static bool bpf_scx_is_valid_access(int off, int size, enum bpf_access_type type, const struct bpf_prog *prog, struct bpf_insn_access_aux *info) { if (type != BPF_READ) return false; if (off < 0 || off >= sizeof(__u64) * MAX_BPF_FUNC_ARGS) return false; if (off % size != 0) return false; return btf_ctx_access(off, size, type, prog, info); } /* common to both forms: only scx.disallow is writable */ static int bpf_scx_btf_struct_access_common(const struct bpf_reg_state *reg, int off, int size) { const struct btf_type *t; t = btf_type_by_id(reg->btf, reg->btf_id); if (t == task_struct_type && off >= offsetof(struct task_struct, scx.disallow) && off + size <= offsetofend(struct task_struct, scx.disallow)) return SCALAR_VALUE; return -EACCES; } static int bpf_scx_btf_struct_access(struct bpf_verifier_log *log, const struct bpf_reg_state *reg, int off, int size) { const struct btf_type *t; t = btf_type_by_id(reg->btf, reg->btf_id); if (t == task_struct_type) { if ((off >= offsetof(struct task_struct, scx.slice) && off + size <= offsetofend(struct task_struct, scx.slice)) || (off >= offsetof(struct task_struct, scx.dsq_vtime) && off + size <= offsetofend(struct task_struct, scx.dsq_vtime))) return SCALAR_VALUE; } return bpf_scx_btf_struct_access_common(reg, off, size); } /* cid-form rejects direct slice and dsq_vtime writes in favor of the kfuncs */ static int bpf_scx_cid_btf_struct_access(struct bpf_verifier_log *log, const struct bpf_reg_state *reg, int off, int size) { return bpf_scx_btf_struct_access_common(reg, off, size); } static const struct bpf_verifier_ops bpf_scx_verifier_ops = { .get_func_proto = bpf_base_func_proto, .is_valid_access = bpf_scx_is_valid_access, .btf_struct_access = bpf_scx_btf_struct_access, }; static const struct bpf_verifier_ops bpf_scx_cid_verifier_ops = { .get_func_proto = bpf_base_func_proto, .is_valid_access = bpf_scx_is_valid_access, .btf_struct_access = bpf_scx_cid_btf_struct_access, }; static int bpf_scx_init_member(const struct btf_type *t, const struct btf_member *member, void *kdata, const void *udata) { const struct sched_ext_ops *uops = udata; struct sched_ext_ops *ops = kdata; u32 moff = __btf_member_bit_offset(t, member) / 8; int ret; switch (moff) { case offsetof(struct sched_ext_ops, dispatch_max_batch): if (*(u32 *)(udata + moff) > INT_MAX) return -E2BIG; ops->dispatch_max_batch = *(u32 *)(udata + moff); return 1; case offsetof(struct sched_ext_ops, flags): if (*(u64 *)(udata + moff) & ~SCX_OPS_ALL_FLAGS) return -EINVAL; ops->flags = *(u64 *)(udata + moff); return 1; case offsetof(struct sched_ext_ops, name): ret = bpf_obj_name_cpy(ops->name, uops->name, sizeof(ops->name)); if (ret < 0) return ret; if (ret == 0) return -EINVAL; return 1; case offsetof(struct sched_ext_ops, timeout_ms): if (msecs_to_jiffies(*(u32 *)(udata + moff)) > SCX_WATCHDOG_MAX_TIMEOUT) return -E2BIG; ops->timeout_ms = *(u32 *)(udata + moff); return 1; case offsetof(struct sched_ext_ops, exit_dump_len): ops->exit_dump_len = *(u32 *)(udata + moff) ?: SCX_EXIT_DUMP_DFL_LEN; return 1; case offsetof(struct sched_ext_ops, hotplug_seq): ops->hotplug_seq = *(u64 *)(udata + moff); return 1; case offsetof(struct sched_ext_ops, cid_shard_size): ops->cid_shard_size = *(u32 *)(udata + moff); return 1; case offsetof(struct sched_ext_ops, rescue_bandwidth_ppt): { u32 bw_ppt = *(u32 *)(udata + moff); if (bw_ppt > SCX_RESCUE_MAX_BW_PPT && bw_ppt != SCX_RESCUE_DISABLE) return -E2BIG; ops->rescue_bandwidth_ppt = bw_ppt; return 1; } case offsetof(struct sched_ext_ops, rescue_quantum_us): { u32 quantum_us = *(u32 *)(udata + moff); if (quantum_us > SCX_RESCUE_MAX_QUANTUM_US) return -E2BIG; if (quantum_us && quantum_us < SCX_RESCUE_MIN_QUANTUM_US) return -EINVAL; ops->rescue_quantum_us = quantum_us; return 1; } #ifdef CONFIG_EXT_SUB_SCHED case offsetof(struct sched_ext_ops, sub_cgroup_id): ops->sub_cgroup_id = *(u64 *)(udata + moff); return 1; #endif /* CONFIG_EXT_SUB_SCHED */ } return 0; } static int bpf_scx_check_member(const struct btf_type *t, const struct btf_member *member, const struct bpf_prog *prog) { u32 moff = __btf_member_bit_offset(t, member) / 8; switch (moff) { case offsetof(struct sched_ext_ops, init_task): #ifdef CONFIG_EXT_GROUP_SCHED case offsetof(struct sched_ext_ops, cgroup_init): case offsetof(struct sched_ext_ops, cgroup_exit): case offsetof(struct sched_ext_ops, cgroup_prep_move): #endif case offsetof(struct sched_ext_ops, cpu_online): case offsetof(struct sched_ext_ops, cpu_offline): case offsetof(struct sched_ext_ops, init_cids): case offsetof(struct sched_ext_ops, init): case offsetof(struct sched_ext_ops, exit): case offsetof(struct sched_ext_ops, sub_attach): case offsetof(struct sched_ext_ops, sub_detach): break; default: if (prog->sleepable) return -EINVAL; } #ifdef CONFIG_EXT_SUB_SCHED /* * Enable private stack for operations that can nest along the * hierarchy. * * XXX - Ideally, we should only do this for scheds that allow * sub-scheds and sub-scheds themselves but I don't know how to access * struct_ops from here. */ switch (moff) { case offsetof(struct sched_ext_ops, dispatch): prog->aux->priv_stack_requested = true; prog->aux->recursion_detected = scx_pstack_recursion_on_dispatch; break; case offsetof(struct sched_ext_ops, sub_caps_updated): prog->aux->priv_stack_requested = true; prog->aux->recursion_detected = scx_pstack_recursion_on_caps_updated; break; } #endif /* CONFIG_EXT_SUB_SCHED */ return 0; } static int bpf_scx_reg(void *kdata, struct bpf_link *link) { struct scx_enable_cmd cmd = { .ops = kdata }; return scx_enable(&cmd, link); } struct scx_arena_scan { struct bpf_map *arena; int err; }; /* * The verifier enforces one arena per BPF program, so each struct_ops * member prog contributes at most one arena via bpf_prog_arena(). * Require all non-NULL contributions to match. */ static int scx_arena_scan_prog(struct bpf_prog *prog, void *data) { struct scx_arena_scan *s = data; struct bpf_map *arena = NULL; /* arena.o, which defines these, is built only on MMU && 64BIT */ #if defined(CONFIG_MMU) && defined(CONFIG_64BIT) arena = bpf_prog_arena(prog); #endif if (!arena) return 0; if (s->arena && s->arena != arena) { s->err = -EINVAL; return 1; } s->arena = arena; return 0; } static int bpf_scx_reg_cid(void *kdata, struct bpf_link *link) { struct scx_enable_cmd cmd = { .ops_cid = kdata, .is_cid_type = true }; struct scx_arena_scan scan = {}; int ret; bpf_struct_ops_for_each_prog(kdata, scx_arena_scan_prog, &scan); if (scan.err) { pr_err("sched_ext: cid-form scheduler uses multiple arena maps\n"); return scan.err; } if (!scan.arena) { pr_err("sched_ext: cid-form scheduler must use a BPF arena map\n"); return -EINVAL; } bpf_map_inc(scan.arena); cmd.arena_map = scan.arena; ret = scx_enable(&cmd, link); if (cmd.arena_map) /* not consumed by scx_alloc_and_add_sched() */ bpf_map_put(cmd.arena_map); return ret; } static void bpf_scx_unreg(void *kdata, struct bpf_link *link) { struct sched_ext_ops *ops = kdata; struct scx_sched *sch = rcu_dereference_protected(ops->priv, true); scx_disable(sch, SCX_EXIT_UNREG); scx_flush_disable_work(sch); RCU_INIT_POINTER(ops->priv, NULL); kobject_put(&sch->kobj); } static int bpf_scx_init(struct btf *btf) { task_struct_type = btf_type_by_id(btf, btf_tracing_ids[BTF_TRACING_TYPE_TASK]); return 0; } static int bpf_scx_update(void *kdata, void *old_kdata, struct bpf_link *link) { /* * sched_ext does not support updating the actively-loaded BPF * scheduler, as registering a BPF scheduler can always fail if the * scheduler returns an error code for e.g. ops.init(), ops.init_task(), * etc. Similarly, we can always race with unregistration happening * elsewhere, such as with sysrq. */ return -EOPNOTSUPP; } static int bpf_scx_validate(void *kdata) { return 0; } static s32 sched_ext_ops__select_cpu(struct task_struct *p, s32 prev_cpu, u64 wake_flags) { return -EINVAL; } static void sched_ext_ops__enqueue(struct task_struct *p, u64 enq_flags) {} static void sched_ext_ops__dequeue(struct task_struct *p, u64 enq_flags) {} static void sched_ext_ops__dispatch(s32 prev_cpu, struct task_struct *prev__nullable) {} static void sched_ext_ops__tick(struct task_struct *p) {} static void sched_ext_ops__runnable(struct task_struct *p, u64 enq_flags) {} static void sched_ext_ops__running(struct task_struct *p) {} static void sched_ext_ops__stopping(struct task_struct *p, bool runnable) {} static void sched_ext_ops__quiescent(struct task_struct *p, u64 deq_flags) {} static bool sched_ext_ops__yield(struct task_struct *from, struct task_struct *to__nullable) { return false; } static bool sched_ext_ops__core_sched_before(struct task_struct *a, struct task_struct *b) { return false; } static void sched_ext_ops__set_weight(struct task_struct *p, u32 weight) {} static void sched_ext_ops__set_cpumask(struct task_struct *p, const struct cpumask *mask) {} static void sched_ext_ops__update_idle(s32 cpu, bool idle) {} static void sched_ext_ops__cpu_acquire(s32 cpu, struct scx_cpu_acquire_args *args) {} static void sched_ext_ops__cpu_release(s32 cpu, struct scx_cpu_release_args *args) {} static s32 sched_ext_ops__init_task(struct task_struct *p, struct scx_init_task_args *args) { return -EINVAL; } static void sched_ext_ops__exit_task(struct task_struct *p, struct scx_exit_task_args *args) {} static void sched_ext_ops__enable(struct task_struct *p) {} static void sched_ext_ops__disable(struct task_struct *p) {} #ifdef CONFIG_EXT_GROUP_SCHED static s32 sched_ext_ops__cgroup_init(struct cgroup *cgrp, struct scx_cgroup_init_args *args) { return -EINVAL; } static void sched_ext_ops__cgroup_exit(struct cgroup *cgrp) {} static s32 sched_ext_ops__cgroup_prep_move(struct task_struct *p, struct cgroup *from, struct cgroup *to) { return -EINVAL; } static void sched_ext_ops__cgroup_move(struct task_struct *p, struct cgroup *from, struct cgroup *to) {} static void sched_ext_ops__cgroup_cancel_move(struct task_struct *p, struct cgroup *from, struct cgroup *to) {} static void sched_ext_ops__cgroup_set_weight(struct cgroup *cgrp, u32 weight) {} static void sched_ext_ops__cgroup_set_bandwidth(struct cgroup *cgrp, u64 period_us, u64 quota_us, u64 burst_us) {} static void sched_ext_ops__cgroup_set_idle(struct cgroup *cgrp, bool idle) {} #endif /* CONFIG_EXT_GROUP_SCHED */ static s32 sched_ext_ops__sub_attach(struct scx_sub_attach_args *args) { return -EINVAL; } static void sched_ext_ops__sub_detach(struct scx_sub_detach_args *args) {} static void sched_ext_ops__cpu_online(s32 cpu) {} static void sched_ext_ops__cpu_offline(s32 cpu) {} static s32 sched_ext_ops__init_cids(void) { return -EINVAL; } static s32 sched_ext_ops__init(void) { return -EINVAL; } static void sched_ext_ops__exit(struct scx_exit_info *info) {} static void sched_ext_ops__dump(struct scx_dump_ctx *ctx) {} static void sched_ext_ops__dump_cpu(struct scx_dump_ctx *ctx, s32 cpu, bool idle) {} static void sched_ext_ops__dump_task(struct scx_dump_ctx *ctx, struct task_struct *p) {} static struct sched_ext_ops __bpf_ops_sched_ext_ops = { .select_cpu = sched_ext_ops__select_cpu, .enqueue = sched_ext_ops__enqueue, .dequeue = sched_ext_ops__dequeue, .dispatch = sched_ext_ops__dispatch, .tick = sched_ext_ops__tick, .runnable = sched_ext_ops__runnable, .running = sched_ext_ops__running, .stopping = sched_ext_ops__stopping, .quiescent = sched_ext_ops__quiescent, .yield = sched_ext_ops__yield, .core_sched_before = sched_ext_ops__core_sched_before, .set_weight = sched_ext_ops__set_weight, .set_cpumask = sched_ext_ops__set_cpumask, .update_idle = sched_ext_ops__update_idle, .cpu_acquire = sched_ext_ops__cpu_acquire, .cpu_release = sched_ext_ops__cpu_release, .init_task = sched_ext_ops__init_task, .exit_task = sched_ext_ops__exit_task, .enable = sched_ext_ops__enable, .disable = sched_ext_ops__disable, #ifdef CONFIG_EXT_GROUP_SCHED .cgroup_init = sched_ext_ops__cgroup_init, .cgroup_exit = sched_ext_ops__cgroup_exit, .cgroup_prep_move = sched_ext_ops__cgroup_prep_move, .cgroup_move = sched_ext_ops__cgroup_move, .cgroup_cancel_move = sched_ext_ops__cgroup_cancel_move, .cgroup_set_weight = sched_ext_ops__cgroup_set_weight, .cgroup_set_bandwidth = sched_ext_ops__cgroup_set_bandwidth, .cgroup_set_idle = sched_ext_ops__cgroup_set_idle, #endif .sub_attach = sched_ext_ops__sub_attach, .sub_detach = sched_ext_ops__sub_detach, .cpu_online = sched_ext_ops__cpu_online, .cpu_offline = sched_ext_ops__cpu_offline, .init_cids = sched_ext_ops__init_cids, .init = sched_ext_ops__init, .exit = sched_ext_ops__exit, .dump = sched_ext_ops__dump, .dump_cpu = sched_ext_ops__dump_cpu, .dump_task = sched_ext_ops__dump_task, }; static struct bpf_struct_ops bpf_sched_ext_ops = { .verifier_ops = &bpf_scx_verifier_ops, .reg = bpf_scx_reg, .unreg = bpf_scx_unreg, .check_member = bpf_scx_check_member, .init_member = bpf_scx_init_member, .init = bpf_scx_init, .update = bpf_scx_update, .validate = bpf_scx_validate, .name = "sched_ext_ops", .owner = THIS_MODULE, .cfi_stubs = &__bpf_ops_sched_ext_ops }; /* * cid-form cfi stubs. Stubs whose signatures match the cpu-form (param types * identical, only param names differ across structs) are reused. Some need * fresh stubs, set_cmask due to an argument type difference and the sub-sched * notifiers because no cpu-form stub exists to reuse. */ static void sched_ext_ops_cid__set_cmask(struct task_struct *p, const struct scx_cmask *cmask__arena) {} static void sched_ext_ops__sub_caps_updated(const struct scx_cmask *cmask__arena, u64 caps) {} static void sched_ext_ops__sub_ecaps_updated(s32 cid, u64 before, u64 after) {} static struct sched_ext_ops_cid __bpf_ops_sched_ext_ops_cid = { .select_cid = sched_ext_ops__select_cpu, .enqueue = sched_ext_ops__enqueue, .dequeue = sched_ext_ops__dequeue, .dispatch = sched_ext_ops__dispatch, .tick = sched_ext_ops__tick, .runnable = sched_ext_ops__runnable, .running = sched_ext_ops__running, .stopping = sched_ext_ops__stopping, .quiescent = sched_ext_ops__quiescent, .yield = sched_ext_ops__yield, .core_sched_before = sched_ext_ops__core_sched_before, .set_weight = sched_ext_ops__set_weight, .set_cmask = sched_ext_ops_cid__set_cmask, .update_idle = sched_ext_ops__update_idle, .init_task = sched_ext_ops__init_task, .exit_task = sched_ext_ops__exit_task, .enable = sched_ext_ops__enable, .disable = sched_ext_ops__disable, #ifdef CONFIG_EXT_GROUP_SCHED .cpuctl_init = sched_ext_ops__cgroup_init, .cpuctl_exit = sched_ext_ops__cgroup_exit, .cpuctl_prep_move = sched_ext_ops__cgroup_prep_move, .cpuctl_move = sched_ext_ops__cgroup_move, .cpuctl_cancel_move = sched_ext_ops__cgroup_cancel_move, .cpuctl_set_weight = sched_ext_ops__cgroup_set_weight, .cpuctl_set_bandwidth = sched_ext_ops__cgroup_set_bandwidth, .cpuctl_set_idle = sched_ext_ops__cgroup_set_idle, #endif .sub_attach = sched_ext_ops__sub_attach, .sub_detach = sched_ext_ops__sub_detach, .sub_caps_updated = sched_ext_ops__sub_caps_updated, .sub_ecaps_updated = sched_ext_ops__sub_ecaps_updated, .cid_online = sched_ext_ops__cpu_online, .cid_offline = sched_ext_ops__cpu_offline, .init_cids = sched_ext_ops__init_cids, .init = sched_ext_ops__init, .exit = sched_ext_ops__exit, .dump = sched_ext_ops__dump, .dump_cid = sched_ext_ops__dump_cpu, .dump_task = sched_ext_ops__dump_task, }; /* * The cid-form struct_ops shares all bpf_struct_ops hooks with the cpu form. * init_member, check_member, reg, unreg, etc. process kdata as the byte block * verified to match by the BUILD_BUG_ON checks in scx_init(). */ static struct bpf_struct_ops bpf_sched_ext_ops_cid = { .verifier_ops = &bpf_scx_cid_verifier_ops, .reg = bpf_scx_reg_cid, .unreg = bpf_scx_unreg, .check_member = bpf_scx_check_member, .init_member = bpf_scx_init_member, .init = bpf_scx_init, .update = bpf_scx_update, .validate = bpf_scx_validate, .name = "sched_ext_ops_cid", .owner = THIS_MODULE, .cfi_stubs = &__bpf_ops_sched_ext_ops_cid }; /******************************************************************************** * System integration and init. */ static void sysrq_handle_sched_ext_reset(u8 key) { struct scx_sched *sch; sch = rcu_dereference(scx_root); if (likely(sch)) scx_disable(sch, SCX_EXIT_SYSRQ); else pr_info("sched_ext: BPF schedulers not loaded\n"); } static const struct sysrq_key_op sysrq_sched_ext_reset_op = { .handler = sysrq_handle_sched_ext_reset, .help_msg = "reset-sched-ext(S)", .action_msg = "Disable sched_ext and revert all tasks to CFS", .enable_mask = SYSRQ_ENABLE_RTNICE, }; static void sysrq_handle_sched_ext_dump(u8 key) { struct scx_exit_info ei = { .kind = SCX_EXIT_NONE, .exit_cpu = -1, .reason = "SysRq-D", }; struct scx_sched *sch; list_for_each_entry_rcu(sch, &scx_sched_all, all) scx_dump_state(sch, &ei, 0, false); } static const struct sysrq_key_op sysrq_sched_ext_dump_op = { .handler = sysrq_handle_sched_ext_dump, .help_msg = "dump-sched-ext(D)", .action_msg = "Trigger sched_ext debug dump", .enable_mask = SYSRQ_ENABLE_RTNICE, }; static bool can_skip_idle_kick(struct rq *rq) { lockdep_assert_rq_held(rq); /* * We can skip idle kicking if @rq is going to go through at least one * full SCX scheduling cycle before going idle. Just checking whether * curr is not idle is insufficient because we could be racing * dispatch_one() trying to pull the next task from a remote rq, which * may fail, and @rq may become idle afterwards. * * The race window is small and we don't and can't guarantee that @rq is * only kicked while idle anyway. Skip only when sure. */ return !is_idle_task(rq->curr) && !(rq->scx.flags & SCX_RQ_IN_DISPATCH); } static bool kick_one_cpu(s32 cpu, struct scx_sched_pcpu *pcpu, struct rq *this_rq, unsigned long *ksyncs) { struct rq *rq = cpu_rq(cpu); struct scx_rq *this_scx = &this_rq->scx; const struct sched_class *cur_class; bool should_wait = false; bool kickable; unsigned long flags; raw_spin_rq_lock_irqsave(rq, flags); cur_class = rq->curr->sched_class; /* * During CPU hotplug, a CPU may depend on kicking itself to make * forward progress. Allow kicking self regardless of online state. If * @cpu is running a higher class task, we have no control over @cpu. * Skip kicking. A sub-sched lacking baseline access on @cid has no * business forcing a reschedule there - skip. This is the authoritative * cap check: ecaps is read here under @rq's lock. */ kickable = (cpu_online(cpu) || cpu == cpu_of(this_rq)) && !sched_class_above(cur_class, &ext_sched_class); if (kickable && !scx_missing_caps(pcpu->sch, cpu, SCX_CAP_BASE)) { if (cpumask_test_cpu(cpu, pcpu->cpus_to_preempt)) { if (cur_class == &ext_sched_class) { u64 caps = scx_caps_for_preempt(pcpu->sch, rq, 0); if (unlikely(scx_missing_caps(pcpu->sch, cpu, caps))) __scx_add_event(pcpu->sch, SCX_EV_SUB_PREEMPT_DENIED, 1); else if (unlikely(!scx_set_task_slice(rq->curr, 0))) __scx_add_event(pcpu->sch, SCX_EV_SLICE_DENIED, 1); } cpumask_clear_cpu(cpu, pcpu->cpus_to_preempt); } if (cpumask_test_cpu(cpu, pcpu->cpus_to_wait)) { if (cur_class == &ext_sched_class) { cpumask_set_cpu(cpu, this_scx->cpus_to_sync); ksyncs[cpu] = rq->scx.kick_sync; should_wait = true; } cpumask_clear_cpu(cpu, pcpu->cpus_to_wait); } resched_curr(rq); } else { /* a kickable cpu was skipped solely for the missing caps */ if (kickable) __scx_add_event(pcpu->sch, SCX_EV_SUB_KICK_DENIED, 1); cpumask_clear_cpu(cpu, pcpu->cpus_to_preempt); cpumask_clear_cpu(cpu, pcpu->cpus_to_wait); } scx_rq_lock_drop(rq); raw_spin_rq_unlock_irqrestore(rq, flags); return should_wait; } static void kick_one_cpu_if_idle(s32 cpu, struct scx_sched_pcpu *pcpu, struct rq *this_rq) { struct rq *rq = cpu_rq(cpu); unsigned long flags; raw_spin_rq_lock_irqsave(rq, flags); /* idle kicks need baseline access too, see kick_one_cpu() */ if (!can_skip_idle_kick(rq) && (cpu_online(cpu) || cpu == cpu_of(this_rq))) { if (likely(!scx_missing_caps(pcpu->sch, cpu, SCX_CAP_BASE))) resched_curr(rq); else __scx_add_event(pcpu->sch, SCX_EV_SUB_KICK_DENIED, 1); } scx_rq_lock_drop(rq); raw_spin_rq_unlock_irqrestore(rq, flags); } static void kick_cpus_irq_workfn(struct irq_work *irq_work) { struct rq *this_rq = this_rq(); struct scx_rq *this_scx = &this_rq->scx; struct scx_kick_syncs __rcu *ksyncs_pcpu = __this_cpu_read(scx_kick_syncs); struct scx_sched_pcpu *pcpu, *tmp; bool should_wait = false; unsigned long *ksyncs; s32 cpu; /* can race with free_kick_syncs() during scheduler disable */ if (unlikely(!ksyncs_pcpu)) return; ksyncs = rcu_dereference_bh(ksyncs_pcpu)->syncs; /* * Walk scheds with pending kicks on this cpu. scx_kick_cpu() adds to * the list under local_irq_save() and only this irq_work consumes it. * A plain list without locking is sufficient. */ list_for_each_entry_safe(pcpu, tmp, &this_scx->sched_pcpus_to_kick, to_kick_node) { list_del_init(&pcpu->to_kick_node); for_each_cpu(cpu, pcpu->cpus_to_kick) { should_wait |= kick_one_cpu(cpu, pcpu, this_rq, ksyncs); cpumask_clear_cpu(cpu, pcpu->cpus_to_kick); cpumask_clear_cpu(cpu, pcpu->cpus_to_kick_if_idle); } for_each_cpu(cpu, pcpu->cpus_to_kick_if_idle) { kick_one_cpu_if_idle(cpu, pcpu, this_rq); cpumask_clear_cpu(cpu, pcpu->cpus_to_kick_if_idle); } } /* * Can't wait in hardirq — kick_sync can't advance, deadlocking if * CPUs wait for each other. Defer to kick_sync_wait_bal_cb(). */ if (should_wait) { raw_spin_rq_lock(this_rq); this_scx->kick_sync_pending = true; resched_curr(this_rq); scx_rq_lock_drop(this_rq); raw_spin_rq_unlock(this_rq); } } /** * print_scx_info - print out sched_ext scheduler state * @log_lvl: the log level to use when printing * @p: target task * * If a sched_ext scheduler is enabled, print the name and state of the * scheduler. If @p is on sched_ext, print further information about the task. * * This function can be safely called on any task as long as the task_struct * itself is accessible. While safe, this function isn't synchronized and may * print out mixups or garbages of limited length. */ void print_scx_info(const char *log_lvl, struct task_struct *p) { struct scx_sched *sch; enum scx_enable_state state = scx_enable_state(); const char *all = READ_ONCE(scx_switching_all) ? "+all" : ""; char runnable_at_buf[22] = "?"; struct sched_class *class; unsigned long runnable_at; guard(rcu)(); sch = scx_task_sched_rcu(p); if (!sch) return; /* * Carefully check if the task was running on sched_ext, and then * carefully copy the time it's been runnable, and its state. */ if (copy_from_kernel_nofault(&class, &p->sched_class, sizeof(class)) || class != &ext_sched_class) { printk("%sSched_ext: %s (%s%s)", log_lvl, sch->ops.name, scx_enable_state_str[state], all); return; } if (!copy_from_kernel_nofault(&runnable_at, &p->scx.runnable_at, sizeof(runnable_at))) scnprintf(runnable_at_buf, sizeof(runnable_at_buf), "%+ldms", jiffies_delta_msecs(runnable_at, jiffies)); /* print everything onto one line to conserve console space */ printk("%sSched_ext: %s (%s%s), task: runnable_at=%s", log_lvl, sch->ops.name, scx_enable_state_str[state], all, runnable_at_buf); } static int scx_pm_handler(struct notifier_block *nb, unsigned long event, void *ptr) { struct scx_sched *sch; guard(rcu)(); sch = rcu_dereference(scx_root); if (!sch) return NOTIFY_OK; /* * SCX schedulers often have userspace components which are sometimes * involved in critial scheduling paths. PM operations involve freezing * userspace which can lead to scheduling misbehaviors including stalls. * Let's bypass while PM operations are in progress. */ switch (event) { case PM_HIBERNATION_PREPARE: case PM_SUSPEND_PREPARE: case PM_RESTORE_PREPARE: scx_bypass(sch, true); break; case PM_POST_HIBERNATION: case PM_POST_SUSPEND: case PM_POST_RESTORE: scx_bypass(sch, false); break; } return NOTIFY_OK; } static struct notifier_block scx_pm_notifier = { .notifier_call = scx_pm_handler, }; void __init init_sched_ext_class(void) { s32 cpu, v; /* * The following is to prevent the compiler from optimizing out the enum * definitions so that BPF scheduler implementations can use them * through the generated vmlinux.h. */ WRITE_ONCE(v, SCX_ENQ_WAKEUP | SCX_DEQ_SLEEP | SCX_KICK_PREEMPT | SCX_TG_ONLINE); scx_idle_init_masks(); for_each_possible_cpu(cpu) { struct rq *rq = cpu_rq(cpu); int n = cpu_to_node(cpu); /* local_dsq's sch will be set during scx_root_enable() */ BUG_ON(scx_init_dsq(&rq->scx.local_dsq, SCX_DSQ_LOCAL, NULL)); #ifdef CONFIG_EXT_SUB_SCHED BUG_ON(scx_init_dsq(&rq->scx.reject_dsq, SCX_DSQ_REJECT, NULL)); scx_rescue_init(rq); #endif INIT_LIST_HEAD(&rq->scx.runnable_list); INIT_LIST_HEAD(&rq->scx.ddsp_deferred_locals); BUG_ON(!zalloc_cpumask_var_node(&rq->scx.cpus_to_sync, GFP_KERNEL, n)); INIT_LIST_HEAD(&rq->scx.sched_pcpus_to_kick); raw_spin_lock_init(&rq->scx.deferred_reenq_lock); INIT_LIST_HEAD(&rq->scx.deferred_reenq_locals); INIT_LIST_HEAD(&rq->scx.deferred_reenq_users); rq->scx.deferred_irq_work = IRQ_WORK_INIT_HARD(deferred_irq_workfn); rq->scx.kick_cpus_irq_work = IRQ_WORK_INIT_HARD(kick_cpus_irq_workfn); if (cpu_online(cpu)) cpu_rq(cpu)->scx.flags |= SCX_RQ_ONLINE; } register_sysrq_key('S', &sysrq_sched_ext_reset_op); register_sysrq_key('D', &sysrq_sched_ext_dump_op); INIT_DELAYED_WORK(&scx_watchdog_work, scx_watchdog_workfn); #ifdef CONFIG_EXT_SUB_SCHED BUG_ON(rhashtable_init(&scx_sched_hash, &scx_sched_hash_params)); #endif /* CONFIG_EXT_SUB_SCHED */ } /******************************************************************************** * Helpers that can be called from the BPF scheduler. */ static bool scx_vet_enq_flags(struct scx_sched *sch, u64 dsq_id, u64 *enq_flags) { bool is_local = dsq_id == SCX_DSQ_LOCAL || (dsq_id & SCX_DSQ_LOCAL_ON) == SCX_DSQ_LOCAL_ON; if (unlikely(*enq_flags & __SCX_ENQ_INTERNAL_MASK)) { scx_error(sch, "invalid enq_flags 0x%llx", *enq_flags); return false; } if (*enq_flags & SCX_ENQ_IMMED) { if (unlikely(!is_local)) { scx_error(sch, "SCX_ENQ_IMMED on a non-local DSQ 0x%llx", dsq_id); return false; } } else if ((sch->ops.flags & SCX_OPS_ALWAYS_ENQ_IMMED) && is_local) { *enq_flags |= SCX_ENQ_IMMED; } if (unlikely((*enq_flags & SCX_ENQ_RESCUE) && !is_local)) { scx_error(sch, "SCX_ENQ_RESCUE on a non-local DSQ 0x%llx", dsq_id); return false; } return true; } static bool scx_dsq_insert_preamble(struct scx_sched *sch, struct task_struct *p, u64 dsq_id, u64 *enq_flags) { lockdep_assert_irqs_disabled(); if (unlikely(!p)) { scx_error(sch, "called with NULL task"); return false; } /* see SCX_EV_INSERT_NOT_OWNED definition */ if (unlikely(!scx_task_on_sched(sch, p))) { __scx_add_event(sch, SCX_EV_INSERT_NOT_OWNED, 1); return false; } if (!scx_vet_enq_flags(sch, dsq_id, enq_flags)) return false; return true; } static void scx_dsq_insert_commit(struct scx_sched *sch, struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) { struct scx_dsp_ctx *dspc = &this_cpu_ptr(sch->pcpu)->dsp_ctx; struct task_struct *ddsp_task; ddsp_task = __this_cpu_read(direct_dispatch_task); if (ddsp_task) { mark_direct_dispatch(sch, ddsp_task, p, dsq_id, slice, vtime, enq_flags); return; } if (unlikely(dspc->cursor >= sch->dsp_max_batch)) { scx_error(sch, "dispatch buffer overflow"); return; } dspc->buf[dspc->cursor++] = (struct scx_dsp_buf_ent){ .task = p, .qseq = atomic_long_read(&p->scx.ops_state) & SCX_OPSS_QSEQ_MASK, .dsq_id = dsq_id, .slice = slice, .vtime = vtime, .enq_flags = enq_flags, }; } __bpf_kfunc_start_defs(); /** * scx_bpf_dsq_insert___v2 - Insert a task into the FIFO queue of a DSQ * @p: task_struct to insert * @dsq_id: DSQ to insert into * @slice: duration @p can run for in nsecs, 0 to keep the current value * @enq_flags: SCX_ENQ_* * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Insert @p into the FIFO queue of the DSQ identified by @dsq_id. It is safe to * call this function spuriously. Can be called from ops.enqueue(), * ops.select_cpu(), and ops.dispatch(). * * When called from ops.select_cpu() or ops.enqueue(), it's for direct dispatch * and @p must match the task being enqueued. * * When called from ops.select_cpu(), @enq_flags and @dsq_id are stored, and @p * will be directly inserted into the corresponding dispatch queue after * ops.select_cpu() returns. If @p is inserted into SCX_DSQ_LOCAL, it will be * inserted into the local DSQ of the CPU returned by ops.select_cpu(). * @enq_flags are OR'd with the enqueue flags on the enqueue path before the * task is inserted. * * When called from ops.dispatch(), there are no restrictions on @p or @dsq_id * and this function can be called upto ops.dispatch_max_batch times to insert * multiple tasks. scx_bpf_dispatch_nr_slots() returns the number of the * remaining slots. scx_bpf_dsq_move_to_local() flushes the batch and resets the * counter. * * This function doesn't have any locking restrictions and may be called under * BPF locks (in the future when BPF introduces more flexible locking). * * @p is allowed to run for @slice. The scheduling path is triggered on slice * exhaustion. If zero, the current residual slice is maintained. If * %SCX_SLICE_INF, @p never expires and the BPF scheduler must kick the CPU with * scx_bpf_kick_cpu() to trigger scheduling. * * Returns %true on successful insertion, %false on failure. On the root * scheduler, %false return triggers scheduler abort and the caller doesn't need * to check the return value. */ __bpf_kfunc bool scx_bpf_dsq_insert___v2(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_flags, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return false; if (!scx_dsq_insert_preamble(sch, p, dsq_id, &enq_flags)) return false; scx_dsq_insert_commit(sch, p, dsq_id, slice, 0, enq_flags); return true; } /* * COMPAT: Will be removed in v6.23 along with the ___v2 suffix. */ __bpf_kfunc void scx_bpf_dsq_insert(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_flags, const struct bpf_prog_aux *aux) { scx_bpf_dsq_insert___v2(p, dsq_id, slice, enq_flags, aux); } static bool scx_dsq_insert_vtime(struct scx_sched *sch, struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) { if (!scx_dsq_insert_preamble(sch, p, dsq_id, &enq_flags)) return false; scx_dsq_insert_commit(sch, p, dsq_id, slice, vtime, enq_flags | SCX_ENQ_DSQ_PRIQ); return true; } struct scx_bpf_dsq_insert_vtime_args { /* @p can't be packed together as KF_RCU is not transitive */ u64 dsq_id; u64 slice; u64 vtime; u64 enq_flags; }; /** * __scx_bpf_dsq_insert_vtime - Arg-wrapped vtime DSQ insertion * @p: task_struct to insert * @args: struct containing the rest of the arguments * @args->dsq_id: DSQ to insert into * @args->slice: duration @p can run for in nsecs, 0 to keep the current value * @args->vtime: @p's ordering inside the vtime-sorted queue of the target DSQ * @args->enq_flags: SCX_ENQ_* * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Wrapper kfunc that takes arguments via struct to work around BPF's 5 argument * limit. BPF programs should use scx_bpf_dsq_insert_vtime() which is provided * as an inline wrapper in common.bpf.h. * * Insert @p into the vtime priority queue of the DSQ identified by * @args->dsq_id. Tasks queued into the priority queue are ordered by * @args->vtime. All other aspects are identical to scx_bpf_dsq_insert(). * * @args->vtime ordering is according to time_before64() which considers * wrapping. A numerically larger vtime may indicate an earlier position in the * ordering and vice-versa. * * A DSQ can only be used as a FIFO or priority queue at any given time and this * function must not be called on a DSQ which already has one or more FIFO tasks * queued and vice-versa. Also, the built-in DSQs (SCX_DSQ_LOCAL and * SCX_DSQ_GLOBAL) cannot be used as priority queues. * * Returns %true on successful insertion, %false on failure. On the root * scheduler, %false return triggers scheduler abort and the caller doesn't need * to check the return value. */ __bpf_kfunc bool __scx_bpf_dsq_insert_vtime(struct task_struct *p, struct scx_bpf_dsq_insert_vtime_args *args, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return false; return scx_dsq_insert_vtime(sch, p, args->dsq_id, args->slice, args->vtime, args->enq_flags); } /* * COMPAT: Will be removed in v6.23. */ __bpf_kfunc void scx_bpf_dsq_insert_vtime(struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) { struct scx_sched *sch; guard(rcu)(); sch = rcu_dereference(scx_root); if (unlikely(!sch)) return; #ifdef CONFIG_EXT_SUB_SCHED /* * Disallow if any sub-scheds are attached. There is no way to tell * which scheduler called us, just error out @p's scheduler. */ if (unlikely(!list_empty(&sch->children))) { scx_error(scx_task_sched(p), "__scx_bpf_dsq_insert_vtime() must be used"); return; } #endif scx_dsq_insert_vtime(sch, p, dsq_id, slice, vtime, enq_flags); } __bpf_kfunc_end_defs(); BTF_KFUNCS_START(scx_kfunc_ids_enqueue_dispatch) BTF_ID_FLAGS(func, scx_bpf_dsq_insert, KF_IMPLICIT_ARGS | KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_insert___v2, KF_IMPLICIT_ARGS | KF_RCU) BTF_ID_FLAGS(func, __scx_bpf_dsq_insert_vtime, KF_IMPLICIT_ARGS | KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_insert_vtime, KF_RCU) BTF_KFUNCS_END(scx_kfunc_ids_enqueue_dispatch) static const struct btf_kfunc_id_set scx_kfunc_set_enqueue_dispatch = { .owner = THIS_MODULE, .set = &scx_kfunc_ids_enqueue_dispatch, .filter = scx_kfunc_context_filter, }; static bool scx_dsq_move(struct bpf_iter_scx_dsq_kern *kit, struct task_struct *p, u64 dsq_id, u64 enq_flags, bool priq) { struct scx_dispatch_q *src_dsq = kit->dsq, *dst_dsq; struct scx_sched *sch; struct rq *p_rq, *src_rq, *locked_rq; bool dispatched = false; unsigned long flags; /* * The verifier considers an iterator slot initialized on any * KF_ITER_NEW return, so a BPF program may legally reach here after * bpf_iter_scx_dsq_new() failed and left @kit->dsq NULL. */ if (unlikely(!src_dsq)) return false; sch = src_dsq->sched; if (!scx_vet_enq_flags(sch, dsq_id, &enq_flags)) return false; /* internal bit, can only go in after @enq_flags is vetted */ if (priq) enq_flags |= SCX_ENQ_DSQ_PRIQ; /* * If the BPF scheduler keeps calling this function repeatedly, it can * cause similar live-lock conditions as scx_consume_dispatch_q(). */ if (unlikely(READ_ONCE(sch->aborting))) return false; if (unlikely(!scx_task_on_sched(sch, p))) { scx_error(sch, "scx_bpf_dsq_move[_vtime]() on %s[%d] but the task belongs to a different scheduler", p->comm, p->pid); return false; } /* * Can be called from either ops.dispatch() holding the dispatched rq's * lock or any context where no rq lock is held. If latter, lock @p's * task_rq which we'll likely need anyway. */ src_rq = task_rq(p); local_irq_save(flags); /* * Under core scheduling, dispatch can run for a sibling rq, so the * locked rq is not necessarily this CPU's. */ locked_rq = scx_locked_rq(); if (locked_rq) { if (locked_rq != src_rq) switch_rq_lock(locked_rq, src_rq); } else { raw_spin_rq_lock(src_rq); } p_rq = src_rq; raw_spin_lock(&src_dsq->lock); /* did someone else get to it while we dropped the locks? */ if (nldsq_cursor_lost_task(&kit->cursor, src_rq, src_dsq, p)) { raw_spin_unlock(&src_dsq->lock); goto out; } /* @p is still on $src_dsq and stable, determine the destination */ dst_dsq = find_dsq_for_dispatch(sch, locked_rq ?: this_rq(), dsq_id, task_cpu(p)); /* * Apply vtime and slice updates before moving. @p is still on $src_dsq * with both $src_dsq and its task_rq locked, satisfying the write * rules, and the PRIQ insertion into $dst_dsq reads the new vtime. */ if (kit->cursor.flags & __SCX_DSQ_ITER_HAS_VTIME) p->scx.dsq_vtime = kit->vtime; if (kit->cursor.flags & __SCX_DSQ_ITER_HAS_SLICE) scx_set_task_slice(p, kit->slice); /* execute move */ p_rq = move_task_between_dsqs(sch, p, enq_flags, src_dsq, dst_dsq); dispatched = true; out: if (locked_rq) { if (locked_rq != p_rq) switch_rq_lock(p_rq, locked_rq); } else { scx_rq_lock_drop(p_rq); raw_spin_rq_unlock_irqrestore(p_rq, flags); } kit->cursor.flags &= ~(__SCX_DSQ_ITER_HAS_SLICE | __SCX_DSQ_ITER_HAS_VTIME); return dispatched; } __bpf_kfunc_start_defs(); /** * scx_bpf_dispatch_nr_slots - Return the number of remaining dispatch slots * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Can only be called from ops.dispatch(). */ __bpf_kfunc u32 scx_bpf_dispatch_nr_slots(const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return 0; return sch->dsp_max_batch - __this_cpu_read(sch->pcpu->dsp_ctx.cursor); } /** * scx_bpf_dispatch_cancel - Cancel the latest dispatch * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Cancel the latest dispatch. Can be called multiple times to cancel further * dispatches. Can only be called from ops.dispatch(). */ __bpf_kfunc void scx_bpf_dispatch_cancel(const struct bpf_prog_aux *aux) { struct scx_sched *sch; struct scx_dsp_ctx *dspc; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return; dspc = &this_cpu_ptr(sch->pcpu)->dsp_ctx; if (dspc->cursor > 0) dspc->cursor--; else scx_error(sch, "dispatch buffer underflow"); } /** * scx_bpf_dsq_move_to_local___v2 - move a task from a DSQ to the current CPU's local DSQ * @dsq_id: DSQ to move task from. Must be a user-created DSQ * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * @enq_flags: %SCX_ENQ_* * * Move a task from the non-local DSQ identified by @dsq_id to the current CPU's * local DSQ for execution with @enq_flags applied. Can only be called from * ops.dispatch(). * * Built-in DSQs (%SCX_DSQ_GLOBAL and %SCX_DSQ_LOCAL*) are not supported as * sources. Local DSQs support reenqueueing (a task can be picked up for * execution, dequeued for property changes, or reenqueued), but the BPF * scheduler cannot directly iterate or move tasks from them. %SCX_DSQ_GLOBAL * is similar but also doesn't support reenqueueing, as it maps to multiple * per-node DSQs making the scope difficult to define; this may change in the * future. * * This function flushes the in-flight dispatches from scx_bpf_dsq_insert() * before trying to move from the specified DSQ. It may also grab rq locks and * thus can't be called under any BPF locks. * * Returns %true if a task has been moved, %false if there isn't any task to * move. */ __bpf_kfunc bool scx_bpf_dsq_move_to_local___v2(u64 dsq_id, u64 enq_flags, const struct bpf_prog_aux *aux) { struct scx_dispatch_q *dsq; struct scx_sched *sch; struct scx_dsp_ctx *dspc; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return false; if (!scx_vet_enq_flags(sch, SCX_DSQ_LOCAL, &enq_flags)) return false; dspc = &this_cpu_ptr(sch->pcpu)->dsp_ctx; scx_flush_dispatch_buf(sch, dspc->rq); dsq = find_user_dsq(sch, dsq_id); if (unlikely(!dsq)) { scx_error(sch, "invalid DSQ ID 0x%016llx", dsq_id); return false; } if (scx_consume_dispatch_q(sch, dspc->rq, dsq, enq_flags)) { /* * A successfully consumed task can be dequeued before it starts * running while the CPU is trying to migrate other dispatched * tasks. Bump nr_tasks to tell dispatch_one() to retry on empty * local DSQ. */ dspc->nr_tasks++; return true; } else { return false; } } /* * COMPAT: ___v2 was introduced in v7.1. Remove this and ___v2 tag in the future. */ __bpf_kfunc bool scx_bpf_dsq_move_to_local(u64 dsq_id, const struct bpf_prog_aux *aux) { return scx_bpf_dsq_move_to_local___v2(dsq_id, 0, aux); } /** * scx_bpf_dsq_move_set_slice - Override slice when moving between DSQs * @it__iter: DSQ iterator in progress * @slice: duration the moved task can run for in nsecs * * Override the slice of the next task that will be moved from @it__iter using * scx_bpf_dsq_move[_vtime](). If this function is not called, the previous * slice duration is kept. */ __bpf_kfunc void scx_bpf_dsq_move_set_slice(struct bpf_iter_scx_dsq *it__iter, u64 slice) { struct bpf_iter_scx_dsq_kern *kit = (void *)it__iter; kit->slice = slice; kit->cursor.flags |= __SCX_DSQ_ITER_HAS_SLICE; } /** * scx_bpf_dsq_move_set_vtime - Override vtime when moving between DSQs * @it__iter: DSQ iterator in progress * @vtime: task's ordering inside the vtime-sorted queue of the target DSQ * * Override the vtime of the next task that will be moved from @it__iter using * scx_bpf_dsq_move_vtime(). If this function is not called, the previous slice * vtime is kept. If scx_bpf_dsq_move() is used to dispatch the next task, the * override is ignored and cleared. */ __bpf_kfunc void scx_bpf_dsq_move_set_vtime(struct bpf_iter_scx_dsq *it__iter, u64 vtime) { struct bpf_iter_scx_dsq_kern *kit = (void *)it__iter; kit->vtime = vtime; kit->cursor.flags |= __SCX_DSQ_ITER_HAS_VTIME; } /** * scx_bpf_dsq_move - Move a task from DSQ iteration to a DSQ * @it__iter: DSQ iterator in progress * @p: task to transfer * @dsq_id: DSQ to move @p to * @enq_flags: SCX_ENQ_* * * Transfer @p which is on the DSQ currently iterated by @it__iter to the DSQ * specified by @dsq_id. All DSQs - local DSQs, global DSQ and user DSQs - can * be the destination. * * For the transfer to be successful, @p must still be on the DSQ and have been * queued before the DSQ iteration started. This function doesn't care whether * @p was obtained from the DSQ iteration. @p just has to be on the DSQ and have * been queued before the iteration started. * * @p's slice is kept by default. Use scx_bpf_dsq_move_set_slice() to update. * * Can be called from ops.dispatch() or any BPF context which doesn't hold a rq * lock (e.g. BPF timers or SYSCALL programs). * * Returns %true if @p has been consumed, %false if @p had already been * consumed, dequeued, or, for sub-scheds, @dsq_id points to a disallowed local * DSQ. */ __bpf_kfunc bool scx_bpf_dsq_move(struct bpf_iter_scx_dsq *it__iter, struct task_struct *p, u64 dsq_id, u64 enq_flags) { return scx_dsq_move((struct bpf_iter_scx_dsq_kern *)it__iter, p, dsq_id, enq_flags, false); } /** * scx_bpf_dsq_move_vtime - Move a task from DSQ iteration to a PRIQ DSQ * @it__iter: DSQ iterator in progress * @p: task to transfer * @dsq_id: DSQ to move @p to * @enq_flags: SCX_ENQ_* * * Transfer @p which is on the DSQ currently iterated by @it__iter to the * priority queue of the DSQ specified by @dsq_id. The destination must be a * user DSQ as only user DSQs support priority queue. * * @p's slice and vtime are kept by default. Use scx_bpf_dsq_move_set_slice() * and scx_bpf_dsq_move_set_vtime() to update. * * All other aspects are identical to scx_bpf_dsq_move(). See * scx_bpf_dsq_insert_vtime() for more information on @vtime. */ __bpf_kfunc bool scx_bpf_dsq_move_vtime(struct bpf_iter_scx_dsq *it__iter, struct task_struct *p, u64 dsq_id, u64 enq_flags) { return scx_dsq_move((struct bpf_iter_scx_dsq_kern *)it__iter, p, dsq_id, enq_flags, true); } __bpf_kfunc_end_defs(); BTF_KFUNCS_START(scx_kfunc_ids_dispatch) BTF_ID_FLAGS(func, scx_bpf_dispatch_nr_slots, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_dispatch_cancel, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_dsq_move_to_local, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_dsq_move_to_local___v2, KF_IMPLICIT_ARGS) /* scx_bpf_dsq_move*() also in scx_kfunc_ids_unlocked: callable from unlocked contexts */ BTF_ID_FLAGS(func, scx_bpf_dsq_move_set_slice, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_move_set_vtime, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_move, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_move_vtime, KF_RCU) #ifdef CONFIG_EXT_SUB_SCHED BTF_ID_FLAGS(func, scx_bpf_sub_dispatch, KF_IMPLICIT_ARGS) #endif BTF_KFUNCS_END(scx_kfunc_ids_dispatch) static const struct btf_kfunc_id_set scx_kfunc_set_dispatch = { .owner = THIS_MODULE, .set = &scx_kfunc_ids_dispatch, .filter = scx_kfunc_context_filter, }; __bpf_kfunc_start_defs(); /** * scx_bpf_reenqueue_local - Re-enqueue tasks on a local DSQ * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Iterate over all of the tasks currently enqueued on the local DSQ of the * caller's CPU, and re-enqueue them in the BPF scheduler. Returns the number of * processed tasks. Can only be called from ops.cpu_release(). */ __bpf_kfunc u32 scx_bpf_reenqueue_local(const struct bpf_prog_aux *aux) { struct scx_sched *sch; struct rq *rq; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return 0; rq = cpu_rq(smp_processor_id()); lockdep_assert_rq_held(rq); return reenq_local(sch, rq, SCX_REENQ_ANY); } __bpf_kfunc_end_defs(); BTF_KFUNCS_START(scx_kfunc_ids_cpu_release) BTF_ID_FLAGS(func, scx_bpf_reenqueue_local, KF_IMPLICIT_ARGS) BTF_KFUNCS_END(scx_kfunc_ids_cpu_release) static const struct btf_kfunc_id_set scx_kfunc_set_cpu_release = { .owner = THIS_MODULE, .set = &scx_kfunc_ids_cpu_release, .filter = scx_kfunc_context_filter, }; __bpf_kfunc_start_defs(); /** * scx_bpf_create_dsq - Create a custom DSQ * @dsq_id: DSQ to create * @node: NUMA node to allocate from * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Create a custom DSQ identified by @dsq_id. Can be called from any sleepable * scx callback, and any BPF_PROG_TYPE_SYSCALL prog. */ __bpf_kfunc s32 scx_bpf_create_dsq(u64 dsq_id, s32 node, const struct bpf_prog_aux *aux) { struct scx_dispatch_q *dsq; struct scx_sched *sch; s32 ret; if (unlikely(node >= (int)nr_node_ids || (node < 0 && node != NUMA_NO_NODE))) return -EINVAL; if (unlikely(dsq_id & SCX_DSQ_FLAG_BUILTIN)) return -EINVAL; dsq = kmalloc_node(sizeof(*dsq), GFP_KERNEL, node); if (!dsq) return -ENOMEM; /* * scx_init_dsq() must be called in GFP_KERNEL context. Init it with * NULL @sch and update afterwards. */ ret = scx_init_dsq(dsq, dsq_id, NULL); if (ret) { kfree(dsq); return ret; } rcu_read_lock(); sch = scx_prog_sched(aux); if (sch) { dsq->sched = sch; ret = rhashtable_lookup_insert_fast(&sch->dsq_hash, &dsq->hash_node, dsq_hash_params); } else { ret = -ENODEV; } rcu_read_unlock(); if (ret) { exit_dsq(dsq); kfree(dsq); } return ret; } __bpf_kfunc_end_defs(); BTF_KFUNCS_START(scx_kfunc_ids_unlocked) BTF_ID_FLAGS(func, scx_bpf_create_dsq, KF_IMPLICIT_ARGS | KF_SLEEPABLE) /* also in scx_kfunc_ids_dispatch: also callable from ops.dispatch() */ BTF_ID_FLAGS(func, scx_bpf_dsq_move_set_slice, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_move_set_vtime, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_move, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_move_vtime, KF_RCU) /* also in scx_kfunc_ids_select_cpu: also callable from ops.select_cpu()/ops.enqueue() */ BTF_ID_FLAGS(func, __scx_bpf_select_cpu_and, KF_IMPLICIT_ARGS | KF_RCU) BTF_ID_FLAGS(func, scx_bpf_select_cpu_and, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_select_cpu_dfl, KF_IMPLICIT_ARGS | KF_RCU) BTF_KFUNCS_END(scx_kfunc_ids_unlocked) static const struct btf_kfunc_id_set scx_kfunc_set_unlocked = { .owner = THIS_MODULE, .set = &scx_kfunc_ids_unlocked, .filter = scx_kfunc_context_filter, }; __bpf_kfunc_start_defs(); /** * scx_bpf_task_set_slice - Set task's time slice * @p: task of interest * @slice: time slice to set in nsecs * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Set @p's time slice. @p must be on the calling scheduler. The value is * applied whether or not the caller holds @p's rq lock - see the slice write * rules above for the ownership model. * * Raising the slice is honored only while the scheduler holds %SCX_CAP_BASE on * @p's cpu, otherwise it is counted in %SCX_EV_SLICE_DENIED. Shortening is * always allowed. On the stashed path the slice is packed into an atomic64_t * with the scheduler id and a flag bit, so a slice too large to fit is clamped * and counted in %SCX_EV_SLICE_CLAMPED. %SCX_SLICE_INF is preserved. * * Return %true on success, %false if @p is not on the calling scheduler. */ __bpf_kfunc bool scx_bpf_task_set_slice(struct task_struct *p, u64 slice, const struct bpf_prog_aux *aux) { struct scx_sched *sch; struct rq *locked_rq; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch || !scx_task_on_sched(sch, p))) return false; /* * Directly write only when we hold the lock of the rq @p is queued or * running on. See the write rules above. * * While @p is queued on a user DSQ or in the BPF scheduler, * synchronization is the scheduler's responsibility. This write can * race a concurrent dispatch's commit, see apply_slice_vtime(). * * Making this kfunc always go through the oob stash would leave the * commit as the only direct writer and close the race, but that would * require two more oob application points - the dispatch keep-prev test * and the tick-time expiry check. */ locked_rq = scx_locked_rq(); if (!locked_rq || (READ_ONCE(p->scx.runnable_cpu) != cpu_of(locked_rq) && !task_current(locked_rq, p))) { set_task_slice_oob(sch, p, slice); return true; } /* under the rq lock: apply now, extensions gated on baseline access */ if (slice > p->scx.slice && unlikely(scx_missing_caps(sch, cpu_of(locked_rq), SCX_CAP_BASE))) { __scx_add_event(sch, SCX_EV_SLICE_DENIED, 1); return true; } if (unlikely(!scx_set_task_slice(p, slice))) __scx_add_event(sch, SCX_EV_SLICE_DENIED, 1); return true; } /** * scx_bpf_task_set_dsq_vtime - Set task's virtual time for DSQ ordering * @p: task of interest * @vtime: virtual time to set * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Set @p's virtual time to @vtime. Returns %true on success, %false if the * calling scheduler doesn't have authority over @p. */ __bpf_kfunc bool scx_bpf_task_set_dsq_vtime(struct task_struct *p, u64 vtime, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch || !scx_task_on_sched(sch, p))) return false; p->scx.dsq_vtime = vtime; return true; } void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags) { struct scx_sched_pcpu *pcpu; struct rq *this_rq; unsigned long irq_flags; /* * The per-cpu kick list is guarded only by local_irq_save(), which does * not mask NMIs, so kicking from NMI could corrupt it and is unsupported. */ if (unlikely(in_nmi())) { scx_error(sch, "scx_bpf_kick_cpu() called from NMI"); return; } local_irq_save(irq_flags); this_rq = this_rq(); pcpu = this_cpu_ptr(sch->pcpu); /* * While bypassing for PM ops, IRQ handling may not be online which can * lead to irq_work_queue() malfunction such as infinite busy wait for * IRQ status update. Suppress kicking. */ if (scx_bypassing(sch, cpu_of(this_rq))) goto out; /* * Actual kicking is bounced to kick_cpus_irq_workfn() to avoid nesting * rq locks. We can probably be smarter and avoid bouncing if called * from ops which don't hold a rq lock. * * The kick masks are owned by @sch->pcpu, so that a preempt kick can be * attributed to @sch. */ if (flags & SCX_KICK_IDLE) { struct rq *target_rq = cpu_rq(cpu); if (unlikely(flags & (SCX_KICK_PREEMPT | SCX_KICK_WAIT))) scx_error(sch, "PREEMPT/WAIT cannot be used with SCX_KICK_IDLE"); if (raw_spin_rq_trylock(target_rq)) { if (can_skip_idle_kick(target_rq)) { scx_rq_lock_drop(target_rq); raw_spin_rq_unlock(target_rq); goto out; } scx_rq_lock_drop(target_rq); raw_spin_rq_unlock(target_rq); } cpumask_set_cpu(cpu, pcpu->cpus_to_kick_if_idle); } else { cpumask_set_cpu(cpu, pcpu->cpus_to_kick); if (flags & SCX_KICK_PREEMPT) cpumask_set_cpu(cpu, pcpu->cpus_to_preempt); if (flags & SCX_KICK_WAIT) cpumask_set_cpu(cpu, pcpu->cpus_to_wait); } if (list_empty(&pcpu->to_kick_node)) list_add_tail(&pcpu->to_kick_node, &this_rq->scx.sched_pcpus_to_kick); irq_work_queue(&this_rq->scx.kick_cpus_irq_work); out: local_irq_restore(irq_flags); } /** * scx_bpf_kick_cpu - Trigger reschedule on a CPU * @cpu: cpu to kick * @flags: %SCX_KICK_* flags * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Kick @cpu into rescheduling. This can be used to wake up an idle CPU or * trigger rescheduling on a busy CPU. This can be called from any online * scx_ops operation and the actual kicking is performed asynchronously through * an irq work. */ __bpf_kfunc void scx_bpf_kick_cpu(s32 cpu, u64 flags, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (likely(sch) && scx_cpu_valid(sch, cpu, NULL)) scx_kick_cpu(sch, cpu, flags); } /** * scx_bpf_kick_cid - Trigger reschedule on the CPU mapped to @cid * @cid: cid to kick * @flags: %SCX_KICK_* flags * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * cid-addressed equivalent of scx_bpf_kick_cpu(). An invalid @cid aborts the * scheduler via scx_cid_to_cpu(). Caps are enforced on the delivery path: a * kick is dropped if the caller lacks baseline access on @cid, and a * %SCX_KICK_PREEMPT degrades to a plain reschedule if the caller lacks * %SCX_CAP_PREEMPT for a task outside its subtree. */ __bpf_kfunc void scx_bpf_kick_cid(s32 cid, u64 flags, const struct bpf_prog_aux *aux) { struct scx_sched *sch; s32 cpu; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return; cpu = scx_cid_to_cpu(sch, cid); if (cpu < 0) return; scx_kick_cpu(sch, cpu, flags); } /** * scx_bpf_dsq_nr_queued - Return the number of queued tasks * @dsq_id: id of the DSQ * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Return the number of tasks in the DSQ matching @dsq_id. If not found, * -%ENOENT is returned. * * %SCX_DSQ_LOCAL resolves to the local DSQ of the rq the current scheduler * operation is locked to - e.g. the rq being dispatched for in ops.dispatch() - * or the calling CPU's when no rq is locked. */ __bpf_kfunc s32 scx_bpf_dsq_nr_queued(u64 dsq_id, const struct bpf_prog_aux *aux) { struct scx_sched *sch; struct scx_dispatch_q *dsq; s32 ret; preempt_disable(); sch = scx_prog_sched(aux); if (unlikely(!sch)) { ret = -ENODEV; goto out; } if (dsq_id == SCX_DSQ_LOCAL) { ret = READ_ONCE((scx_locked_rq() ?: this_rq())->scx.local_dsq.nr); goto out; } else if ((dsq_id & SCX_DSQ_LOCAL_ON) == SCX_DSQ_LOCAL_ON) { s32 cpu = scx_cpu_ret(sch, dsq_id & SCX_DSQ_LOCAL_CPU_MASK); if (scx_cpu_valid(sch, cpu, NULL)) { ret = READ_ONCE(cpu_rq(cpu)->scx.local_dsq.nr); goto out; } } else { dsq = find_user_dsq(sch, dsq_id); if (dsq) { ret = READ_ONCE(dsq->nr); goto out; } } ret = -ENOENT; out: preempt_enable(); return ret; } /** * scx_bpf_destroy_dsq - Destroy a custom DSQ * @dsq_id: DSQ to destroy * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Destroy the custom DSQ identified by @dsq_id. Only DSQs created with * scx_bpf_create_dsq() can be destroyed. The caller must ensure that the DSQ is * empty and no further tasks are dispatched to it. Ignored if called on a DSQ * which doesn't exist. Can be called from any online scx_ops operations. */ __bpf_kfunc void scx_bpf_destroy_dsq(u64 dsq_id, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (sch) destroy_dsq(sch, dsq_id); } /** * bpf_iter_scx_dsq_new - Create a DSQ iterator * @it: iterator to initialize * @dsq_id: DSQ to iterate * @flags: %SCX_DSQ_ITER_* * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Initialize BPF iterator @it which can be used with bpf_for_each() to walk * tasks in the DSQ specified by @dsq_id. Iteration using @it only includes * tasks which are already queued when this function is invoked. */ __bpf_kfunc int bpf_iter_scx_dsq_new(struct bpf_iter_scx_dsq *it, u64 dsq_id, u64 flags, const struct bpf_prog_aux *aux) { struct bpf_iter_scx_dsq_kern *kit = (void *)it; struct scx_sched *sch; BUILD_BUG_ON(sizeof(struct bpf_iter_scx_dsq_kern) > sizeof(struct bpf_iter_scx_dsq)); BUILD_BUG_ON(__alignof__(struct bpf_iter_scx_dsq_kern) != __alignof__(struct bpf_iter_scx_dsq)); BUILD_BUG_ON(__SCX_DSQ_ITER_ALL_FLAGS & ((1U << __SCX_DSQ_LNODE_PRIV_SHIFT) - 1)); /* * next() and destroy() will be called regardless of the return value. * Always clear $kit->dsq. */ kit->dsq = NULL; sch = scx_prog_sched(aux); if (unlikely(!sch)) return -ENODEV; if (flags & ~__SCX_DSQ_ITER_USER_FLAGS) return -EINVAL; kit->dsq = find_user_dsq(sch, dsq_id); if (!kit->dsq) return -ENOENT; kit->cursor = INIT_DSQ_LIST_CURSOR(kit->cursor, kit->dsq, flags); return 0; } /** * bpf_iter_scx_dsq_next - Progress a DSQ iterator * @it: iterator to progress * * Return the next task. See bpf_iter_scx_dsq_new(). */ __bpf_kfunc struct task_struct *bpf_iter_scx_dsq_next(struct bpf_iter_scx_dsq *it) { struct bpf_iter_scx_dsq_kern *kit = (void *)it; if (!kit->dsq) return NULL; guard(raw_spinlock_irqsave)(&kit->dsq->lock); return nldsq_cursor_next_task(&kit->cursor, kit->dsq); } /** * bpf_iter_scx_dsq_destroy - Destroy a DSQ iterator * @it: iterator to destroy * * Undo scx_iter_scx_dsq_new(). */ __bpf_kfunc void bpf_iter_scx_dsq_destroy(struct bpf_iter_scx_dsq *it) { struct bpf_iter_scx_dsq_kern *kit = (void *)it; if (!kit->dsq) return; if (!list_empty(&kit->cursor.node)) { unsigned long flags; raw_spin_lock_irqsave(&kit->dsq->lock, flags); list_del_init(&kit->cursor.node); raw_spin_unlock_irqrestore(&kit->dsq->lock, flags); } kit->dsq = NULL; } /** * scx_bpf_dsq_peek - Lockless peek at the first element. * @dsq_id: DSQ to examine. * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Read the first element in the DSQ. This is semantically equivalent to using * the DSQ iterator, but is lockfree. Of course, like any lockless operation, * this provides only a point-in-time snapshot, and the contents may change * by the time any subsequent locking operation reads the queue. * * Returns the pointer, or NULL indicates an empty queue OR internal error. */ __bpf_kfunc struct task_struct *scx_bpf_dsq_peek(u64 dsq_id, const struct bpf_prog_aux *aux) { struct scx_sched *sch; struct scx_dispatch_q *dsq; sch = scx_prog_sched(aux); if (unlikely(!sch)) return NULL; if (unlikely(dsq_id & SCX_DSQ_FLAG_BUILTIN)) { scx_error(sch, "peek disallowed on builtin DSQ 0x%llx", dsq_id); return NULL; } dsq = find_user_dsq(sch, dsq_id); if (unlikely(!dsq)) { scx_error(sch, "peek on non-existent DSQ 0x%llx", dsq_id); return NULL; } return rcu_dereference(dsq->first_task); } /** * scx_bpf_dsq_reenq - Re-enqueue tasks on a DSQ * @dsq_id: DSQ to re-enqueue * @reenq_flags: %SCX_RENQ_* * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Iterate over all of the tasks currently enqueued on the DSQ identified by * @dsq_id, and re-enqueue them in the BPF scheduler. The following DSQs are * supported: * * - Local DSQs (%SCX_DSQ_LOCAL or %SCX_DSQ_LOCAL_ON | $cpu) * - User DSQs * * Re-enqueues are performed asynchronously. Can be called from anywhere. * * %SCX_DSQ_LOCAL resolves to the local DSQ of the rq the current scheduler * operation is locked to - e.g. the rq being dispatched for in ops.dispatch() - * or the calling CPU's when no rq is locked. */ __bpf_kfunc void scx_bpf_dsq_reenq(u64 dsq_id, u64 reenq_flags, const struct bpf_prog_aux *aux) { struct rq *locked_rq = scx_locked_rq(); struct scx_sched *sch; struct scx_dispatch_q *dsq; guard(preempt)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return; if (unlikely(reenq_flags & ~__SCX_REENQ_USER_MASK)) { scx_error(sch, "invalid SCX_REENQ flags 0x%llx", reenq_flags); return; } /* not specifying any filter bits is the same as %SCX_REENQ_ANY */ if (!(reenq_flags & __SCX_REENQ_FILTER_MASK)) reenq_flags |= SCX_REENQ_ANY; dsq = find_dsq_for_dispatch(sch, locked_rq ?: this_rq(), dsq_id, smp_processor_id()); schedule_dsq_reenq(sch, dsq, reenq_flags, locked_rq); } /** * scx_bpf_reenqueue_local___v2 - Re-enqueue tasks on a local DSQ * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Iterate over all of the tasks currently enqueued on the local DSQ of the * caller's CPU, and re-enqueue them in the BPF scheduler. Can be called from * anywhere. * * This is now a special case of scx_bpf_dsq_reenq() and may be removed in the * future. */ __bpf_kfunc void scx_bpf_reenqueue_local___v2(const struct bpf_prog_aux *aux) { scx_bpf_dsq_reenq(SCX_DSQ_LOCAL, 0, aux); } __bpf_kfunc_end_defs(); __printf(5, 0) static s32 __bstr_format(struct scx_sched *sch, u64 *data_buf, char *line_buf, size_t line_size, char *fmt, unsigned long long *data, u32 data__sz) { struct bpf_bprintf_data bprintf_data = { .get_bin_args = true }; s32 ret; if (data__sz % 8 || data__sz > MAX_BPRINTF_VARARGS * 8 || (data__sz && !data)) { scx_error(sch, "invalid data=%p and data__sz=%u", (void *)data, data__sz); return -EINVAL; } ret = copy_from_kernel_nofault(data_buf, data, data__sz); if (ret < 0) { scx_error(sch, "failed to read data fields (%d)", ret); return ret; } ret = bpf_bprintf_prepare(fmt, UINT_MAX, data_buf, data__sz / 8, &bprintf_data); if (ret < 0) { scx_error(sch, "format preparation failed (%d)", ret); return ret; } ret = bstr_printf(line_buf, line_size, fmt, bprintf_data.bin_args); bpf_bprintf_cleanup(&bprintf_data); if (ret < 0) { scx_error(sch, "(\"%s\", %p, %u) failed to format", fmt, data, data__sz); return ret; } return ret; } /* * Exit @sch with the reason formatted from a BPF-supplied bstr format. The exit * is claimed first and the reason is formatted directly into the winner-owned * exit_info buffer, which allows use from any context including NMI. * * @fmt_blame is the sched blamed for formatting failures through the * scx_error() calls in __bstr_format() and differs from @sch when a parent * supplies the kill reason for a child. A formatting failure doesn't revert the * claim - @sch still exits with the claimed kind and a fallback message. */ __printf(5, 0) bool scx_exit_bstr(struct scx_sched *sch, enum scx_exit_kind kind, s64 exit_code, struct scx_sched *fmt_blame, char *fmt, unsigned long long *data, u32 data__sz) { struct scx_exit_info *ei = sch->exit_info; u64 data_buf[MAX_BPRINTF_VARARGS]; s32 ret; guard(preempt)(); if (!scx_claim_exit(sch, kind)) return false; ret = __bstr_format(fmt_blame, data_buf, ei->msg, SCX_EXIT_MSG_LEN, fmt, data, data__sz); if (ret < 0) scnprintf(ei->msg, SCX_EXIT_MSG_LEN, "exit message formatting failed (%d)", ret); scx_finish_exit(sch, kind, exit_code, raw_smp_processor_id()); return true; } __bpf_kfunc_start_defs(); /** * scx_bpf_exit_bstr - Gracefully exit the BPF scheduler. * @exit_code: Exit value to pass to user space via struct scx_exit_info. * @fmt: error message format string * @data: format string parameters packaged using ___bpf_fill() macro * @data__sz: @data len, must end in '__sz' for the verifier * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Indicate that the BPF scheduler wants to exit gracefully, and initiate ops * disabling. */ __printf(2, 0) __bpf_kfunc void scx_bpf_exit_bstr(s64 exit_code, char *fmt, unsigned long long *data, u32 data__sz, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (likely(sch)) scx_exit_bstr(sch, SCX_EXIT_UNREG_BPF, exit_code, sch, fmt, data, data__sz); } /** * scx_bpf_error_bstr - Indicate fatal error * @fmt: error message format string * @data: format string parameters packaged using ___bpf_fill() macro * @data__sz: @data len, must end in '__sz' for the verifier * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Indicate that the BPF scheduler encountered a fatal error and initiate ops * disabling. */ __printf(1, 0) __bpf_kfunc void scx_bpf_error_bstr(char *fmt, unsigned long long *data, u32 data__sz, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (likely(sch)) scx_exit_bstr(sch, SCX_EXIT_ERROR_BPF, 0, sch, fmt, data, data__sz); } /** * scx_bpf_dump_bstr - Generate extra debug dump specific to the BPF scheduler * @fmt: format string * @data: format string parameters packaged using ___bpf_fill() macro * @data__sz: @data len, must end in '__sz' for the verifier * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * To be called through scx_bpf_dump() helper from ops.dump(), dump_cpu() and * dump_task() to generate extra debug dump specific to the BPF scheduler. * * The extra dump may be multiple lines. A single line may be split over * multiple calls. The last line is automatically terminated. */ __printf(1, 0) __bpf_kfunc void scx_bpf_dump_bstr(char *fmt, unsigned long long *data, u32 data__sz, const struct bpf_prog_aux *aux) { struct scx_sched *sch; struct scx_dump_data *dd = &scx_dump_data; struct scx_bstr_buf *buf = &dd->buf; s32 ret; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return; if (raw_smp_processor_id() != dd->cpu) { scx_error(sch, "scx_bpf_dump() must only be called from ops.dump() and friends"); return; } /* append the formatted string to the line buf */ ret = __bstr_format(sch, buf->data, buf->line + dd->cursor, sizeof(buf->line) - dd->cursor, fmt, data, data__sz); if (ret < 0) { scx_dump_line(dd->s, "%s[!] (\"%s\", %p, %u) failed to format (%d)", dd->prefix, fmt, data, data__sz, ret); return; } dd->cursor += ret; dd->cursor = min_t(s32, dd->cursor, sizeof(buf->line)); if (!dd->cursor) return; /* * If the line buf overflowed or ends in a newline, flush it into the * dump. This is to allow the caller to generate a single line over * multiple calls. As ops_dump_flush() can also handle multiple lines in * the line buf, the only case which can lead to an unexpected * truncation is when the caller keeps generating newlines in the middle * instead of the end consecutively. Don't do that. */ if (dd->cursor >= sizeof(buf->line) || buf->line[dd->cursor - 1] == '\n') ops_dump_flush(); } /** * scx_bpf_cpuperf_cap - Query the maximum relative capacity of a CPU * @cpu: CPU of interest * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Return the maximum relative capacity of @cpu in relation to the most * performant CPU in the system. The return value is in the range [1, * %SCX_CPUPERF_ONE]. See scx_bpf_cpuperf_cur(). */ __bpf_kfunc u32 scx_bpf_cpuperf_cap(s32 cpu, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (likely(sch) && scx_cpu_valid(sch, cpu, NULL)) return arch_scale_cpu_capacity(cpu); else return SCX_CPUPERF_ONE; } /** * scx_bpf_cidperf_cap - Query the maximum relative capacity of the CPU at @cid * @cid: cid of the CPU to query * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * cid-addressed equivalent of scx_bpf_cpuperf_cap(). */ __bpf_kfunc u32 scx_bpf_cidperf_cap(s32 cid, const struct bpf_prog_aux *aux) { struct scx_sched *sch; s32 cpu; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return SCX_CPUPERF_ONE; cpu = scx_cid_to_cpu(sch, cid); if (cpu < 0) return SCX_CPUPERF_ONE; return arch_scale_cpu_capacity(cpu); } /** * scx_bpf_cpuperf_cur - Query the current relative performance of a CPU * @cpu: CPU of interest * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Return the current relative performance of @cpu in relation to its maximum. * The return value is in the range [1, %SCX_CPUPERF_ONE]. * * The current performance level of a CPU in relation to the maximum performance * available in the system can be calculated as follows: * * scx_bpf_cpuperf_cap() * scx_bpf_cpuperf_cur() / %SCX_CPUPERF_ONE * * The result is in the range [1, %SCX_CPUPERF_ONE]. */ __bpf_kfunc u32 scx_bpf_cpuperf_cur(s32 cpu, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (likely(sch) && scx_cpu_valid(sch, cpu, NULL)) return arch_scale_freq_capacity(cpu); else return SCX_CPUPERF_ONE; } /** * scx_bpf_cidperf_cur - Query the current performance of the CPU at @cid * @cid: cid of the CPU to query * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * cid-addressed equivalent of scx_bpf_cpuperf_cur(). */ __bpf_kfunc u32 scx_bpf_cidperf_cur(s32 cid, const struct bpf_prog_aux *aux) { struct scx_sched *sch; s32 cpu; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return SCX_CPUPERF_ONE; cpu = scx_cid_to_cpu(sch, cid); if (cpu < 0) return SCX_CPUPERF_ONE; return arch_scale_freq_capacity(cpu); } /* validate and apply a cpuperf target, see scx_bpf_cpuperf_set() */ static s32 scx_cpuperf_set(struct scx_sched *sch, s32 cpu, u32 perf) { struct rq *rq, *locked_rq; struct rq_flags rf; s32 ret; if (unlikely(perf > SCX_CPUPERF_ONE)) { scx_error(sch, "Invalid cpuperf target %u for CPU %d", perf, cpu); return -EINVAL; } if (!scx_cpu_valid(sch, cpu, NULL)) return -EINVAL; rq = cpu_rq(cpu); locked_rq = scx_locked_rq(); /* * When called with an rq lock held, restrict the operation to the * corresponding CPU to prevent ABBA deadlocks. */ if (locked_rq && rq != locked_rq) { scx_error(sch, "Invalid target CPU %d", cpu); return -EINVAL; } /* * If no rq lock is held, allow to operate on any CPU by acquiring * the corresponding rq lock. */ if (!locked_rq) { rq_lock_irqsave(rq, &rf); update_rq_clock(rq); } /* * ecaps updates are folded under the rq lock, making this test * authoritative: a write can never land after a revoke has taken * effect on @cpu. */ if (likely(!scx_missing_caps(sch, cpu, SCX_CAP_PERF))) { rq->scx.cpuperf_target = perf; cpufreq_update_util(rq, 0); ret = 0; } else { __scx_add_event(sch, SCX_EV_SUB_CIDPERF_DENIED, 1); ret = -EACCES; } if (!locked_rq) rq_unlock_irqrestore(rq, &rf); return ret; } /** * scx_bpf_cpuperf_set - Set the relative performance target of a CPU * @cpu: CPU of interest * @perf: target performance level [0, %SCX_CPUPERF_ONE] * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Set the target performance level of @cpu to @perf. @perf is in linear * relative scale between 0 and %SCX_CPUPERF_ONE. This determines how the * schedutil cpufreq governor chooses the target frequency. * * The actual performance level chosen, CPU grouping, and the overhead and * latency of the operations are dependent on the hardware and cpufreq driver in * use. Consult hardware and cpufreq documentation for more information. The * current performance level can be monitored using scx_bpf_cpuperf_cur(). */ __bpf_kfunc void scx_bpf_cpuperf_set(s32 cpu, u32 perf, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return; scx_cpuperf_set(sch, cpu, perf); } /** * scx_bpf_cidperf_set - Set the performance target of the CPU at @cid * @cid: cid of the CPU to target * @perf: target performance level [0, %SCX_CPUPERF_ONE] * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * cid-addressed equivalent of scx_bpf_cpuperf_set(). A sub-sched needs * SCX_CAP_PERF on @cid. Returns 0 if the target was applied, -%EACCES if * the write was denied for missing caps, other -errnos if @cid didn't * resolve. */ __bpf_kfunc s32 scx_bpf_cidperf_set(s32 cid, u32 perf, const struct bpf_prog_aux *aux) { struct scx_sched *sch; s32 cpu; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return -ENODEV; cpu = scx_cid_to_cpu(sch, cid); if (cpu < 0) return cpu; return scx_cpuperf_set(sch, cpu, perf); } /** * scx_bpf_nr_node_ids - Return the number of possible node IDs * * All valid node IDs in the system are smaller than the returned value. */ __bpf_kfunc u32 scx_bpf_nr_node_ids(void) { return nr_node_ids; } /** * scx_bpf_nr_cpu_ids - Return the number of possible CPU IDs * * All valid CPU IDs in the system are smaller than the returned value. */ __bpf_kfunc u32 scx_bpf_nr_cpu_ids(void) { return nr_cpu_ids; } /** * scx_bpf_nr_cids - Return the size of the cid space * * Equals num_possible_cpus(). All valid cids are in [0, return value). */ __bpf_kfunc u32 scx_bpf_nr_cids(void) { return num_possible_cpus(); } /** * scx_bpf_nr_online_cids - Return current count of online CPUs in cid space * * Return num_online_cpus(). The standard model restarts the scheduler on * hotplug, which lets schedulers treat [0, nr_online_cids) as the online * range. Schedulers that prefer to handle hotplug without a restart should * install a custom mapping via scx_bpf_cid_override() and track onlining * through the ops.cid_online / ops.cid_offline callbacks. */ __bpf_kfunc u32 scx_bpf_nr_online_cids(void) { return num_online_cpus(); } /** * scx_bpf_this_cid - Return the cid of the CPU this program is running on * * cid-addressed equivalent of bpf_get_smp_processor_id() for scx programs. * The current cpu is trivially valid, so this is just a table lookup. Return * -EINVAL if called before any scheduler has ever published its cid tables. */ __bpf_kfunc s32 scx_bpf_this_cid(void) { s16 *tbl; guard(rcu)(); tbl = rcu_dereference(scx_cpu_to_cid_tbl); if (!tbl) return -EINVAL; return tbl[raw_smp_processor_id()]; } /** * scx_bpf_get_possible_cpumask - Get a referenced kptr to cpu_possible_mask */ __bpf_kfunc const struct cpumask *scx_bpf_get_possible_cpumask(void) { return cpu_possible_mask; } /** * scx_bpf_get_online_cpumask - Get a referenced kptr to cpu_online_mask */ __bpf_kfunc const struct cpumask *scx_bpf_get_online_cpumask(void) { return cpu_online_mask; } /** * scx_bpf_put_cpumask - Release a possible/online cpumask * @cpumask: cpumask to release */ __bpf_kfunc void scx_bpf_put_cpumask(const struct cpumask *cpumask) { /* * Empty function body because we aren't actually acquiring or releasing * a reference to a global cpumask, which is read-only in the caller and * is never released. The acquire / release semantics here are just used * to make the cpumask is a trusted pointer in the caller. */ } /** * scx_bpf_task_running - Is task currently running? * @p: task of interest */ __bpf_kfunc bool scx_bpf_task_running(const struct task_struct *p) { return task_rq(p)->curr == p; } /** * scx_bpf_task_cpu - CPU a task is currently associated with * @p: task of interest */ __bpf_kfunc s32 scx_bpf_task_cpu(const struct task_struct *p) { return task_cpu(p); } /** * scx_bpf_task_cid - cid a task is currently associated with * @p: task of interest * * cid-addressed equivalent of scx_bpf_task_cpu(). task_cpu(p) is always a * valid cpu, so this is just a table lookup. Return -EINVAL if called before * any scheduler has ever published its cid tables. */ __bpf_kfunc s32 scx_bpf_task_cid(const struct task_struct *p) { s16 *tbl; /* KF_RCU covers only @p - a sleepable program holds no RCU lock */ guard(rcu)(); tbl = rcu_dereference(scx_cpu_to_cid_tbl); if (!tbl) return -EINVAL; return tbl[task_cpu(p)]; } /** * scx_bpf_locked_rq - Return the rq currently locked by SCX * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Returns the rq if a rq lock is currently held by SCX. * Otherwise emits an error and returns NULL. */ __bpf_kfunc struct rq *scx_bpf_locked_rq(const struct bpf_prog_aux *aux) { struct scx_sched *sch; struct rq *rq; guard(preempt)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return NULL; rq = scx_locked_rq(); if (!rq) { scx_error(sch, "accessing rq without holding rq lock"); return NULL; } return rq; } /** * scx_bpf_cpu_curr - Return remote CPU's curr task * @cpu: CPU of interest * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Callers must hold RCU read lock (KF_RCU). */ __bpf_kfunc struct task_struct *scx_bpf_cpu_curr(s32 cpu, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return NULL; if (!scx_cpu_valid(sch, cpu, NULL)) return NULL; return rcu_dereference(cpu_rq(cpu)->curr); } /** * scx_bpf_cid_curr - Return the curr task on the CPU at @cid * @cid: cid of interest * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * cid-addressed equivalent of scx_bpf_cpu_curr(). Callers must hold RCU * read lock (KF_RCU). */ __bpf_kfunc struct task_struct *scx_bpf_cid_curr(s32 cid, const struct bpf_prog_aux *aux) { struct scx_sched *sch; s32 cpu; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return NULL; cpu = scx_cid_to_cpu(sch, cid); if (cpu < 0) return NULL; return rcu_dereference(cpu_rq(cpu)->curr); } /** * scx_bpf_tid_to_task - Look up a task by its scx tid * @tid: task ID previously read from p->scx.tid * * Returns the task with the given tid, or NULL if no such task exists. The * returned pointer is valid until the end of the current RCU read section * (KF_RCU_PROTECTED). Requires SCX_OPS_TID_TO_TASK to be set on the root * scheduler; otherwise an error is raised and NULL returned. */ __bpf_kfunc struct task_struct *scx_bpf_tid_to_task(u64 tid) { struct sched_ext_entity *scx; if (!scx_tid_to_task_enabled()) { struct scx_sched *sch = rcu_dereference(scx_root); if (sch) scx_error(sch, "scx_bpf_tid_to_task() called without SCX_OPS_TID_TO_TASK"); return NULL; } scx = rhashtable_lookup(&scx_tid_hash, &tid, scx_tid_hash_params); if (!scx) return NULL; return container_of(scx, struct task_struct, scx); } u64 __scx_bpf_now(struct rq *rq) { /* the caller must be on @rq's cpu or hold its lock */ lockdep_assert((rq == this_rq() && !preemptible()) || lockdep_is_held(__rq_lockp(rq))); if (smp_load_acquire(&rq->scx.flags) & SCX_RQ_CLK_VALID) { /* if the rq clock is valid, use the cached rq clock */ return READ_ONCE(rq->scx.clock); } else { /* * Otherwise, return a fresh rq clock. * * The rq clock is updated outside of the rq lock. * In this case, keep the updated rq clock invalid so the next * read outside the rq lock gets a fresh rq clock. */ return sched_clock_cpu(cpu_of(rq)); } } /** * scx_bpf_now - Returns a high-performance monotonically non-decreasing * clock for the current CPU. The clock returned is in nanoseconds. * * It provides the following properties: * * 1) High performance: Many BPF schedulers call bpf_ktime_get_ns() frequently * to account for execution time and track tasks' runtime properties. * Unfortunately, in some hardware platforms, bpf_ktime_get_ns() -- which * eventually reads a hardware timestamp counter -- is neither performant nor * scalable. scx_bpf_now() aims to provide a high-performance clock by * using the rq clock in the scheduler core whenever possible. * * 2) High enough resolution for the BPF scheduler use cases: In most BPF * scheduler use cases, the required clock resolution is lower than the most * accurate hardware clock (e.g., rdtsc in x86). scx_bpf_now() basically * uses the rq clock in the scheduler core whenever it is valid. It considers * that the rq clock is valid from the time the rq clock is updated * (update_rq_clock) until the rq is unlocked (rq_unpin_lock). * * 3) Monotonically non-decreasing clock for the same CPU: scx_bpf_now() * guarantees the clock never goes backward when comparing them in the same * CPU. On the other hand, when comparing clocks in different CPUs, there * is no such guarantee -- the clock can go backward. It provides a * monotonically *non-decreasing* clock so that it would provide the same * clock values in two different scx_bpf_now() calls in the same CPU * during the same period of when the rq clock is valid. */ __bpf_kfunc u64 scx_bpf_now(void) { /* * Note that scx_bpf_now() is re-entrant between a process context and * an interrupt context (e.g., timer interrupt). However, we don't need * to consider the race between them because such race is not observable * from a caller. */ guard(preempt)(); return __scx_bpf_now(this_rq()); } static void scx_read_events(struct scx_sched *sch, struct scx_event_stats *events) { int cpu; /* Aggregate per-CPU event counters into @events. */ memset(events, 0, sizeof(*events)); for_each_possible_cpu(cpu) { struct scx_event_stats *e_cpu = &per_cpu_ptr(sch->pcpu, cpu)->event_stats; #define SCX_EVENT(name) (events->name += READ_ONCE(e_cpu->name)) SCX_EVENTS_LIST(SCX_EVENT); #undef SCX_EVENT } } /** * scx_bpf_events - Read the event counters of the calling scheduler * @events: output buffer from a BPF program * @events__sz: @events len, must end in '__sz' for the verifier * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Read the event counters of the scheduler associated with the calling program. * @events is zeroed when no scheduler can be resolved. */ __bpf_kfunc void scx_bpf_events(struct scx_event_stats *events, size_t events__sz, const struct bpf_prog_aux *aux) { struct scx_sched *sch; struct scx_event_stats e_sys; rcu_read_lock(); sch = scx_prog_sched(aux); if (sch) scx_read_events(sch, &e_sys); else memset(&e_sys, 0, sizeof(e_sys)); rcu_read_unlock(); /* * We cannot entirely trust a BPF-provided size since a BPF program * might be compiled against a different vmlinux.h, of which * scx_event_stats would be larger (a newer vmlinux.h) or smaller * (an older vmlinux.h). Hence, we use the smaller size to avoid * memory corruption. */ events__sz = min(events__sz, sizeof(*events)); memcpy(events, &e_sys, events__sz); } #ifdef CONFIG_CGROUP_SCHED /** * scx_bpf_task_cgroup - Return the sched cgroup of a task * @p: task of interest * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * @p->sched_task_group->css.cgroup represents the cgroup @p is associated with * from the scheduler's POV. SCX operations should use this function to * determine @p's current cgroup as, unlike following @p->cgroups, * @p->sched_task_group is stable for the duration of the SCX op. See * SCX_CALL_OP_TASK() for details. */ __bpf_kfunc struct cgroup *scx_bpf_task_cgroup(struct task_struct *p, const struct bpf_prog_aux *aux) { struct task_group *tg = p->sched_task_group; struct cgroup *cgrp = &cgrp_dfl_root.cgrp; struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) goto out; if (!scx_kf_arg_task_ok(sch, p)) goto out; cgrp = tg_cgrp(tg); out: cgroup_get(cgrp); return cgrp; } #endif /* CONFIG_CGROUP_SCHED */ __bpf_kfunc_end_defs(); BTF_KFUNCS_START(scx_kfunc_ids_any) BTF_ID_FLAGS(func, scx_bpf_task_set_slice, KF_IMPLICIT_ARGS | KF_RCU); BTF_ID_FLAGS(func, scx_bpf_task_set_dsq_vtime, KF_IMPLICIT_ARGS | KF_RCU); BTF_ID_FLAGS(func, scx_bpf_kick_cpu, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_kick_cid, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_dsq_nr_queued, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_destroy_dsq, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_dsq_peek, KF_IMPLICIT_ARGS | KF_RCU_PROTECTED | KF_RET_NULL) BTF_ID_FLAGS(func, scx_bpf_dsq_reenq, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_reenqueue_local___v2, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, bpf_iter_scx_dsq_new, KF_IMPLICIT_ARGS | KF_ITER_NEW | KF_RCU_PROTECTED) BTF_ID_FLAGS(func, bpf_iter_scx_dsq_next, KF_ITER_NEXT | KF_RET_NULL) BTF_ID_FLAGS(func, bpf_iter_scx_dsq_destroy, KF_ITER_DESTROY) BTF_ID_FLAGS(func, scx_bpf_exit_bstr, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_error_bstr, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_dump_bstr, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_cpuperf_cap, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_cpuperf_cur, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_cpuperf_set, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_cidperf_cap, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_cidperf_cur, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_cidperf_set, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_nr_node_ids) BTF_ID_FLAGS(func, scx_bpf_nr_cpu_ids) BTF_ID_FLAGS(func, scx_bpf_nr_cids) BTF_ID_FLAGS(func, scx_bpf_nr_online_cids) BTF_ID_FLAGS(func, scx_bpf_this_cid) BTF_ID_FLAGS(func, scx_bpf_get_possible_cpumask, KF_ACQUIRE) BTF_ID_FLAGS(func, scx_bpf_get_online_cpumask, KF_ACQUIRE) BTF_ID_FLAGS(func, scx_bpf_put_cpumask, KF_RELEASE) BTF_ID_FLAGS(func, scx_bpf_task_running, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_task_cid, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_locked_rq, KF_IMPLICIT_ARGS | KF_RET_NULL) BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED) BTF_ID_FLAGS(func, scx_bpf_cid_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED) BTF_ID_FLAGS(func, scx_bpf_tid_to_task, KF_RET_NULL | KF_RCU_PROTECTED) BTF_ID_FLAGS(func, scx_bpf_now) BTF_ID_FLAGS(func, scx_bpf_events, KF_IMPLICIT_ARGS) #ifdef CONFIG_CGROUP_SCHED BTF_ID_FLAGS(func, scx_bpf_task_cgroup, KF_IMPLICIT_ARGS | KF_RCU | KF_ACQUIRE) #endif BTF_ID_FLAGS(func, scx_bpf_sub_grant, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_sub_revoke, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_sub_caps, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_sub_kill_bstr, KF_IMPLICIT_ARGS) BTF_KFUNCS_END(scx_kfunc_ids_any) static const struct btf_kfunc_id_set scx_kfunc_set_any = { .owner = THIS_MODULE, .set = &scx_kfunc_ids_any, .filter = scx_kfunc_context_filter, }; /* * cpu-form kfuncs that are forbidden from cid-form schedulers * (bpf_sched_ext_ops_cid). Programs targeting the cid struct_ops type must * use the cid-form alternative (cid/cmask kfuncs). * * Membership overlaps with scx_kfunc_ids_{any,idle,select_cpu}; the filter * tests this set independently and rejects matches before the per-op * allow-list check runs. * * pahole/resolve_btfids scans every BTF_ID_FLAGS() at build time and * intersects flags across duplicate entries, so each entry must carry the * same flags as the kfunc's primary declaration; otherwise the flags get * dropped globally. */ BTF_KFUNCS_START(scx_kfunc_ids_cpu_only) BTF_ID_FLAGS(func, scx_bpf_kick_cpu, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED) BTF_ID_FLAGS(func, scx_bpf_cpu_node, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_cpuperf_cap, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_cpuperf_cur, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_cpuperf_set, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_get_possible_cpumask, KF_ACQUIRE) BTF_ID_FLAGS(func, scx_bpf_get_online_cpumask, KF_ACQUIRE) BTF_ID_FLAGS(func, scx_bpf_put_cpumask, KF_RELEASE) BTF_ID_FLAGS(func, scx_bpf_select_cpu_dfl, KF_IMPLICIT_ARGS | KF_RCU) BTF_ID_FLAGS(func, __scx_bpf_select_cpu_and, KF_IMPLICIT_ARGS | KF_RCU) BTF_ID_FLAGS(func, scx_bpf_select_cpu_and, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_get_idle_cpumask, KF_IMPLICIT_ARGS | KF_ACQUIRE) BTF_ID_FLAGS(func, scx_bpf_get_idle_cpumask_node, KF_IMPLICIT_ARGS | KF_ACQUIRE) BTF_ID_FLAGS(func, scx_bpf_get_idle_smtmask, KF_IMPLICIT_ARGS | KF_ACQUIRE) BTF_ID_FLAGS(func, scx_bpf_get_idle_smtmask_node, KF_IMPLICIT_ARGS | KF_ACQUIRE) BTF_ID_FLAGS(func, scx_bpf_put_idle_cpumask, KF_RELEASE) BTF_ID_FLAGS(func, scx_bpf_test_and_clear_cpu_idle, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu, KF_IMPLICIT_ARGS | KF_RCU) BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu_node, KF_IMPLICIT_ARGS | KF_RCU) BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu, KF_IMPLICIT_ARGS | KF_RCU) BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu_node, KF_IMPLICIT_ARGS | KF_RCU) BTF_KFUNCS_END(scx_kfunc_ids_cpu_only) /* * Per-op kfunc allow flags. Each bit corresponds to a context-sensitive kfunc * group; an op may permit zero or more groups, with the union expressed in * scx_kf_allow_flags[]. The verifier-time filter (scx_kfunc_context_filter()) * consults this table to decide whether a context-sensitive kfunc is callable * from a given SCX op. */ enum scx_kf_allow_flags { SCX_KF_ALLOW_UNLOCKED = 1 << 0, SCX_KF_ALLOW_INIT_CIDS = 1 << 1, SCX_KF_ALLOW_CPU_RELEASE = 1 << 2, SCX_KF_ALLOW_DISPATCH = 1 << 3, SCX_KF_ALLOW_ENQUEUE = 1 << 4, SCX_KF_ALLOW_SELECT_CPU = 1 << 5, }; /* * Map each SCX op to the union of kfunc groups it permits, indexed by * SCX_OP_IDX(op). Ops not listed only permit kfuncs that are not * context-sensitive. */ static const u32 scx_kf_allow_flags[] = { [SCX_OP_IDX(select_cpu)] = SCX_KF_ALLOW_SELECT_CPU | SCX_KF_ALLOW_ENQUEUE, [SCX_OP_IDX(enqueue)] = SCX_KF_ALLOW_SELECT_CPU | SCX_KF_ALLOW_ENQUEUE, [SCX_OP_IDX(dispatch)] = SCX_KF_ALLOW_ENQUEUE | SCX_KF_ALLOW_DISPATCH, [SCX_OP_IDX(cpu_release)] = SCX_KF_ALLOW_CPU_RELEASE, [SCX_OP_IDX(init_task)] = SCX_KF_ALLOW_UNLOCKED, [SCX_OP_IDX(dump)] = SCX_KF_ALLOW_UNLOCKED, #ifdef CONFIG_EXT_GROUP_SCHED [SCX_OP_IDX(cgroup_init)] = SCX_KF_ALLOW_UNLOCKED, [SCX_OP_IDX(cgroup_exit)] = SCX_KF_ALLOW_UNLOCKED, [SCX_OP_IDX(cgroup_prep_move)] = SCX_KF_ALLOW_UNLOCKED, [SCX_OP_IDX(cgroup_cancel_move)] = SCX_KF_ALLOW_UNLOCKED, [SCX_OP_IDX(cgroup_set_weight)] = SCX_KF_ALLOW_UNLOCKED, [SCX_OP_IDX(cgroup_set_bandwidth)] = SCX_KF_ALLOW_UNLOCKED, [SCX_OP_IDX(cgroup_set_idle)] = SCX_KF_ALLOW_UNLOCKED, #endif /* CONFIG_EXT_GROUP_SCHED */ [SCX_OP_IDX(sub_attach)] = SCX_KF_ALLOW_UNLOCKED, [SCX_OP_IDX(sub_detach)] = SCX_KF_ALLOW_UNLOCKED, [SCX_OP_IDX(sub_ecaps_updated)] = SCX_KF_ALLOW_ENQUEUE | SCX_KF_ALLOW_DISPATCH, [SCX_OP_IDX(cpu_online)] = SCX_KF_ALLOW_UNLOCKED, [SCX_OP_IDX(cpu_offline)] = SCX_KF_ALLOW_UNLOCKED, [SCX_OP_IDX(init_cids)] = SCX_KF_ALLOW_UNLOCKED | SCX_KF_ALLOW_INIT_CIDS, [SCX_OP_IDX(init)] = SCX_KF_ALLOW_UNLOCKED, [SCX_OP_IDX(exit)] = SCX_KF_ALLOW_UNLOCKED, }; /* * Verifier-time filter for SCX kfuncs. Registered via the .filter field on * each per-group btf_kfunc_id_set. The BPF core invokes this for every kfunc * call in the registered hook (BPF_PROG_TYPE_STRUCT_OPS or * BPF_PROG_TYPE_SYSCALL), regardless of which set originally introduced the * kfunc - so the filter must short-circuit on kfuncs it doesn't govern by * falling through to "allow" when none of the SCX sets contain the kfunc. */ int scx_kfunc_context_filter(const struct bpf_prog *prog, u32 kfunc_id) { bool in_unlocked = btf_id_set8_contains(&scx_kfunc_ids_unlocked, kfunc_id); bool in_init_cids = btf_id_set8_contains(&scx_kfunc_ids_init_cids, kfunc_id); bool in_select_cpu = btf_id_set8_contains(&scx_kfunc_ids_select_cpu, kfunc_id); bool in_enqueue = btf_id_set8_contains(&scx_kfunc_ids_enqueue_dispatch, kfunc_id); bool in_dispatch = btf_id_set8_contains(&scx_kfunc_ids_dispatch, kfunc_id); bool in_cpu_release = btf_id_set8_contains(&scx_kfunc_ids_cpu_release, kfunc_id); bool in_idle = btf_id_set8_contains(&scx_kfunc_ids_idle, kfunc_id); bool in_any = btf_id_set8_contains(&scx_kfunc_ids_any, kfunc_id); bool in_cpu_only = btf_id_set8_contains(&scx_kfunc_ids_cpu_only, kfunc_id); bool in_cid = btf_id_set8_contains(&scx_kfunc_ids_cid, kfunc_id); u32 moff, flags; /* Not an SCX kfunc - allow. */ if (!(in_unlocked || in_init_cids || in_select_cpu || in_enqueue || in_dispatch || in_cpu_release || in_idle || in_any || in_cid)) return 0; /* SYSCALL progs (e.g. BPF test_run()) may call unlocked and select_cpu kfuncs. */ if (prog->type == BPF_PROG_TYPE_SYSCALL) return (in_unlocked || in_select_cpu || in_idle || in_any || in_cid) ? 0 : -EACCES; if (prog->type != BPF_PROG_TYPE_STRUCT_OPS) return (in_any || in_idle || in_cid) ? 0 : -EACCES; /* * add_subprog_and_kfunc() collects all kfunc calls, including dead code * guarded by bpf_ksym_exists(), before check_attach_btf_id() sets * prog->aux->st_ops. Allow all kfuncs when st_ops is not yet set; * do_check_main() re-runs the filter with st_ops set and enforces the * actual restrictions. */ if (!prog->aux->st_ops) return 0; /* * Non-SCX struct_ops: SCX kfuncs are not permitted. * * Both bpf_sched_ext_ops (cpu-form) and bpf_sched_ext_ops_cid * (cid-form) are valid SCX struct_ops. Member offsets match between * the two (verified by BUILD_BUG_ON in scx_init()), so the shared * scx_kf_allow_flags[] table indexed by SCX_MOFF_IDX(moff) applies to * both. */ if (prog->aux->st_ops != &bpf_sched_ext_ops && prog->aux->st_ops != &bpf_sched_ext_ops_cid) return -EACCES; /* * cid-form schedulers must use cid/cmask kfuncs. cid and cpu are both * small s32s and trivially confused, so cpu-only kfuncs are rejected at * load time. The reverse (cpu-form calling cid-form kfuncs) is * intentionally permissive to ease gradual cpumask -> cid migration. */ if (prog->aux->st_ops == &bpf_sched_ext_ops_cid && in_cpu_only) return -EACCES; /* SCX struct_ops: check the per-op allow list. */ if (in_any || in_idle || in_cid) return 0; moff = prog->aux->attach_st_ops_member_off; flags = scx_kf_allow_flags[SCX_MOFF_IDX(moff)]; if ((flags & SCX_KF_ALLOW_UNLOCKED) && in_unlocked) return 0; if ((flags & SCX_KF_ALLOW_INIT_CIDS) && in_init_cids) return 0; if ((flags & SCX_KF_ALLOW_CPU_RELEASE) && in_cpu_release) return 0; if ((flags & SCX_KF_ALLOW_DISPATCH) && in_dispatch) return 0; if ((flags & SCX_KF_ALLOW_ENQUEUE) && in_enqueue) return 0; if ((flags & SCX_KF_ALLOW_SELECT_CPU) && in_select_cpu) return 0; return -EACCES; } static int __init scx_init(void) { int ret; /* * sched_ext_ops_cid mirrors sched_ext_ops up to and including @priv. * Both bpf_scx_init_member() and bpf_scx_check_member() use offsets * from struct sched_ext_ops; sched_ext_ops_cid relies on those offsets * matching for the shared fields. Catch any drift at boot. */ #define CID_OFFSET_MATCH(cpu_field, cid_field) \ BUILD_BUG_ON(offsetof(struct sched_ext_ops, cpu_field) != \ offsetof(struct sched_ext_ops_cid, cid_field)) /* data fields used by bpf_scx_init_member() */ CID_OFFSET_MATCH(dispatch_max_batch, dispatch_max_batch); CID_OFFSET_MATCH(flags, flags); CID_OFFSET_MATCH(name, name); CID_OFFSET_MATCH(timeout_ms, timeout_ms); CID_OFFSET_MATCH(exit_dump_len, exit_dump_len); CID_OFFSET_MATCH(hotplug_seq, hotplug_seq); CID_OFFSET_MATCH(cid_shard_size, cid_shard_size); CID_OFFSET_MATCH(rescue_bandwidth_ppt, rescue_bandwidth_ppt); CID_OFFSET_MATCH(rescue_quantum_us, rescue_quantum_us); CID_OFFSET_MATCH(sub_cgroup_id, sub_cgroup_id); /* shared callbacks: the union view requires byte-for-byte offset match */ CID_OFFSET_MATCH(enqueue, enqueue); CID_OFFSET_MATCH(dequeue, dequeue); CID_OFFSET_MATCH(dispatch, dispatch); CID_OFFSET_MATCH(tick, tick); CID_OFFSET_MATCH(runnable, runnable); CID_OFFSET_MATCH(running, running); CID_OFFSET_MATCH(stopping, stopping); CID_OFFSET_MATCH(quiescent, quiescent); CID_OFFSET_MATCH(yield, yield); CID_OFFSET_MATCH(core_sched_before, core_sched_before); CID_OFFSET_MATCH(set_weight, set_weight); CID_OFFSET_MATCH(update_idle, update_idle); CID_OFFSET_MATCH(init_task, init_task); CID_OFFSET_MATCH(exit_task, exit_task); CID_OFFSET_MATCH(enable, enable); CID_OFFSET_MATCH(disable, disable); CID_OFFSET_MATCH(dump, dump); CID_OFFSET_MATCH(dump_task, dump_task); CID_OFFSET_MATCH(sub_attach, sub_attach); CID_OFFSET_MATCH(sub_detach, sub_detach); CID_OFFSET_MATCH(sub_caps_updated, sub_caps_updated); CID_OFFSET_MATCH(sub_ecaps_updated, sub_ecaps_updated); CID_OFFSET_MATCH(init_cids, init_cids); CID_OFFSET_MATCH(init, init); CID_OFFSET_MATCH(exit, exit); /* renamed callbacks must occupy the same slot as their cpu-form sibling */ CID_OFFSET_MATCH(select_cpu, select_cid); CID_OFFSET_MATCH(set_cpumask, set_cmask); CID_OFFSET_MATCH(cpu_online, cid_online); CID_OFFSET_MATCH(cpu_offline, cid_offline); CID_OFFSET_MATCH(dump_cpu, dump_cid); #ifdef CONFIG_EXT_GROUP_SCHED CID_OFFSET_MATCH(cgroup_init, cpuctl_init); CID_OFFSET_MATCH(cgroup_exit, cpuctl_exit); CID_OFFSET_MATCH(cgroup_prep_move, cpuctl_prep_move); CID_OFFSET_MATCH(cgroup_move, cpuctl_move); CID_OFFSET_MATCH(cgroup_cancel_move, cpuctl_cancel_move); CID_OFFSET_MATCH(cgroup_set_weight, cpuctl_set_weight); CID_OFFSET_MATCH(cgroup_set_bandwidth, cpuctl_set_bandwidth); CID_OFFSET_MATCH(cgroup_set_idle, cpuctl_set_idle); #endif /* @priv tail must align since both share the same data block */ CID_OFFSET_MATCH(priv, priv); /* * cid-form must end exactly at @priv - scx_validate_ops() skips * cpu_acquire/cpu_release for cid-form because reading those fields * past the BPF allocation would be UB. */ BUILD_BUG_ON(offsetof(struct sched_ext_ops_cid, __end) != offsetofend(struct sched_ext_ops, priv)); #undef CID_OFFSET_MATCH /* * kfunc registration can't be done from init_sched_ext_class() as * register_btf_kfunc_id_set() needs most of the system to be up. * * Some kfuncs are context-sensitive and can only be called from * specific SCX ops. They are grouped into per-context BTF sets, each * registered with scx_kfunc_context_filter as its .filter callback. The * BPF core dedups identical filter pointers per hook * (btf_populate_kfunc_set()), so the filter is invoked exactly once per * kfunc lookup; it consults scx_kf_allow_flags[] to enforce per-op * restrictions at verify time. */ if ((ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_enqueue_dispatch)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_dispatch)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_cpu_release)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_unlocked)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &scx_kfunc_set_unlocked)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_any)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &scx_kfunc_set_any)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &scx_kfunc_set_any))) { pr_err("sched_ext: Failed to register kfunc sets (%d)\n", ret); return ret; } ret = scx_idle_init(); if (ret) { pr_err("sched_ext: Failed to initialize idle tracking (%d)\n", ret); return ret; } ret = scx_cid_kfunc_init(); if (ret) { pr_err("sched_ext: Failed to register cid kfuncs (%d)\n", ret); return ret; } ret = register_bpf_struct_ops(&bpf_sched_ext_ops, sched_ext_ops); if (ret) { pr_err("sched_ext: Failed to register struct_ops (%d)\n", ret); return ret; } ret = register_bpf_struct_ops(&bpf_sched_ext_ops_cid, sched_ext_ops_cid); if (ret) { pr_err("sched_ext: Failed to register cid struct_ops (%d)\n", ret); return ret; } ret = register_pm_notifier(&scx_pm_notifier); if (ret) { pr_err("sched_ext: Failed to register PM notifier (%d)\n", ret); return ret; } scx_kset = kset_create_and_add("sched_ext", &scx_uevent_ops, kernel_kobj); if (!scx_kset) { pr_err("sched_ext: Failed to create /sys/kernel/sched_ext\n"); return -ENOMEM; } ret = sysfs_create_group(&scx_kset->kobj, &scx_global_attr_group); if (ret < 0) { pr_err("sched_ext: Failed to add global attributes\n"); return ret; } return 0; } __initcall(scx_init);