1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * stop-task scheduling class. 4 * 5 * The stop task is the highest priority task in the system, it preempts 6 * everything and will be preempted by nothing. 7 * 8 * See kernel/stop_machine.c 9 */ 10 #include "sched.h" 11 12 static int 13 select_task_rq_stop(struct task_struct *p, int cpu, int flags) 14 { 15 return task_cpu(p); /* stop tasks as never migrate */ 16 } 17 18 static int 19 balance_stop(struct rq *rq, struct rq_flags *rf) 20 { 21 return sched_stop_runnable(rq); 22 } 23 24 static void 25 wakeup_preempt_stop(struct rq *rq, struct task_struct *p, int flags) 26 { 27 /* we're never preempted */ 28 } 29 30 static void set_next_task_stop(struct rq *rq, struct task_struct *stop, enum snt_e type) 31 { 32 if (type == SNT_REPICK) 33 return; 34 35 stop->se.exec_start = rq_clock_task(rq); 36 } 37 38 static struct task_struct *pick_task_stop(struct rq *rq, struct rq_flags *rf) 39 { 40 if (!sched_stop_runnable(rq)) 41 return NULL; 42 43 return rq->stop; 44 } 45 46 static void 47 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags) 48 { 49 add_nr_running(rq, 1); 50 } 51 52 static bool 53 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags) 54 { 55 sub_nr_running(rq, 1); 56 return true; 57 } 58 59 static void yield_task_stop(struct rq *rq) 60 { 61 BUG(); /* the stop task should never yield, its pointless. */ 62 } 63 64 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev, struct task_struct *next) 65 { 66 update_curr_common(rq); 67 } 68 69 /* 70 * scheduler tick hitting a task of our scheduling class. 71 * 72 * NOTE: This function can be called remotely by the tick offload that 73 * goes along full dynticks. Therefore no local assumption can be made 74 * and everything must be accessed through the @rq and @curr passed in 75 * parameters. 76 */ 77 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued) 78 { 79 } 80 81 static void switching_to_stop(struct rq *rq, struct task_struct *p) 82 { 83 BUG(); /* its impossible to change to this class */ 84 } 85 86 static void 87 prio_changed_stop(struct rq *rq, struct task_struct *p, u64 oldprio) 88 { 89 if (p->prio == oldprio) 90 return; 91 92 BUG(); /* how!?, what priority? */ 93 } 94 95 static void update_curr_stop(struct rq *rq) 96 { 97 } 98 99 /* 100 * Simple, special scheduling class for the per-CPU stop tasks: 101 */ 102 DEFINE_SCHED_CLASS(stop) = { 103 .enqueue_task = enqueue_task_stop, 104 .dequeue_task = dequeue_task_stop, 105 .yield_task = yield_task_stop, 106 107 .wakeup_preempt = wakeup_preempt_stop, 108 109 .pick_task = pick_task_stop, 110 .put_prev_task = put_prev_task_stop, 111 .set_next_task = set_next_task_stop, 112 113 .balance = balance_stop, 114 .select_task_rq = select_task_rq_stop, 115 .set_cpus_allowed = set_cpus_allowed_common, 116 117 .task_tick = task_tick_stop, 118 119 .prio_changed = prio_changed_stop, 120 .switching_to = switching_to_stop, 121 .update_curr = update_curr_stop, 122 }; 123