xref: /linux/kernel/cgroup/cpuset.c (revision 7db28abbea0f7dc1ec4fdfdc149db5fbd9e4c994)

// SPDX-License-Identifier: GPL-2.0
/*
 *  kernel/cpuset.c
 *
 *  Processor and Memory placement constraints for sets of tasks.
 *
 *  Copyright (C) 2003 BULL SA.
 *  Copyright (C) 2004-2007 Silicon Graphics, Inc.
 *  Copyright (C) 2006 Google, Inc
 *
 *  Portions derived from Patrick Mochel's sysfs code.
 *  sysfs is Copyright (c) 2001-3 Patrick Mochel
 *
 *  2003-10-10 Written by Simon Derr.
 *  2003-10-22 Updates by Stephen Hemminger.
 *  2004 May-July Rework by Paul Jackson.
 *  2006 Rework by Paul Menage to use generic cgroups
 *  2008 Rework of the scheduler domains and CPU hotplug handling
 *       by Max Krasnyansky
 */
#include "cpuset-internal.h"

#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/mempolicy.h>
#include <linux/mm.h>
#include <linux/memory.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/sched/deadline.h>
#include <linux/sched/mm.h>
#include <linux/sched/task.h>
#include <linux/security.h>
#include <linux/oom.h>
#include <linux/sched/isolation.h>
#include <linux/wait.h>
#include <linux/workqueue.h>
#include <linux/task_work.h>
#include <linux/llist.h>

DEFINE_STATIC_KEY_FALSE(cpusets_pre_enable_key);
DEFINE_STATIC_KEY_FALSE(cpusets_enabled_key);

/*
 * There could be abnormal cpuset configurations for cpu or memory
 * node binding, add this key to provide a quick low-cost judgment
 * of the situation.
 */
DEFINE_STATIC_KEY_FALSE(cpusets_insane_config_key);

static const char * const perr_strings[] = {
	[PERR_INVCPUS]   = "Invalid cpu list in cpuset.cpus.exclusive",
	[PERR_INVPARENT] = "Parent is an invalid partition root",
	[PERR_NOTPART]   = "Parent is not a partition root",
	[PERR_NOTEXCL]   = "Cpu list in cpuset.cpus not exclusive",
	[PERR_NOCPUS]    = "Parent unable to distribute cpu downstream",
	[PERR_HOTPLUG]   = "No cpu available due to hotplug",
	[PERR_CPUSEMPTY] = "cpuset.cpus and cpuset.cpus.exclusive are empty",
	[PERR_HKEEPING]  = "partition config conflicts with housekeeping setup",
	[PERR_ACCESS]    = "Enable partition not permitted",
	[PERR_REMOTE]    = "Have remote partition underneath",
};

/*
 * CPUSET Locking Convention
 * -------------------------
 *
 * Below are the four global/local locks guarding cpuset structures in lock
 * acquisition order:
 *  - cpuset_top_mutex
 *  - cpu_hotplug_lock (cpus_read_lock/cpus_write_lock)
 *  - cpuset_mutex
 *  - callback_lock (raw spinlock)
 *
 * As cpuset will now indirectly flush a number of different workqueues in
 * housekeeping_update() to update housekeeping cpumasks when the set of
 * isolated CPUs is going to be changed, it may be vulnerable to deadlock
 * if we hold cpus_read_lock while calling into housekeeping_update().
 *
 * The first cpuset_top_mutex will be held except when calling into
 * cpuset_handle_hotplug() from the CPU hotplug code where cpus_write_lock
 * and cpuset_mutex will be held instead. The main purpose of this mutex
 * is to prevent regular cpuset control file write actions from interfering
 * with the call to housekeeping_update(), though CPU hotplug operation can
 * still happen in parallel. This mutex also provides protection for some
 * internal variables.
 *
 * A task must hold all the remaining three locks to modify externally visible
 * or used fields of cpusets, though some of the internally used cpuset fields
 * and internal variables can be modified without holding callback_lock. If only
 * reliable read access of the externally used fields are needed, a task can
 * hold either cpuset_mutex or callback_lock which are exposed to other
 * external subsystems.
 *
 * If a task holds cpu_hotplug_lock and cpuset_mutex, it blocks others,
 * ensuring that it is the only task able to also acquire callback_lock and
 * be able to modify cpusets.  It can perform various checks on the cpuset
 * structure first, knowing nothing will change. It can also allocate memory
 * without holding callback_lock. While it is performing these checks, various
 * callback routines can briefly acquire callback_lock to query cpusets.  Once
 * it is ready to make the changes, it takes callback_lock, blocking everyone
 * else.
 *
 * Calls to the kernel memory allocator cannot be made while holding
 * callback_lock which is a spinlock, as the memory allocator may sleep or
 * call back into cpuset code and acquire callback_lock.
 *
 * Now, the task_struct fields mems_allowed and mempolicy may be changed
 * by other task, we use alloc_lock in the task_struct fields to protect
 * them.
 *
 * The cpuset_common_seq_show() handlers only hold callback_lock across
 * small pieces of code, such as when reading out possibly multi-word
 * cpumasks and nodemasks.
 */

static DEFINE_MUTEX(cpuset_top_mutex);
static DEFINE_MUTEX(cpuset_mutex);

/*
 * File level internal variables below follow one of the following exclusion
 * rules.
 *
 * RWCS: Read/write-able by holding either cpus_write_lock (and optionally
 *	 cpuset_mutex) or both cpus_read_lock and cpuset_mutex.
 *
 * CSCB: Readable by holding either cpuset_mutex or callback_lock. Writable
 *	 by holding both cpuset_mutex and callback_lock.
 *
 * T:	 Read/write-able by holding the cpuset_top_mutex.
 */

/*
 * For local partitions, update to subpartitions_cpus & isolated_cpus is done
 * in update_parent_effective_cpumask(). For remote partitions, it is done in
 * the remote_partition_*() and remote_cpus_update() helpers.
 */
/*
 * Exclusive CPUs distributed out to local or remote sub-partitions of
 * top_cpuset
 */
static cpumask_var_t	subpartitions_cpus;	/* RWCS */

/*
 * Exclusive CPUs in isolated partitions (shown in cpuset.cpus.isolated)
 */
static cpumask_var_t	isolated_cpus;		/* CSCB */

/*
 * Set if housekeeping cpumasks are to be updated.
 */
static bool		update_housekeeping;	/* RWCS */

/*
 * Copy of isolated_cpus to be passed to housekeeping_update()
 */
static cpumask_var_t	isolated_hk_cpus;	/* T */

/*
 * A flag to force sched domain rebuild at the end of an operation.
 * It can be set in
 *  - update_partition_sd_lb()
 *  - update_cpumasks_hier()
 *  - cpuset_update_flag()
 *  - cpuset_hotplug_update_tasks()
 *  - cpuset_handle_hotplug()
 *
 * Protected by cpuset_mutex (with cpus_read_lock held) or cpus_write_lock.
 *
 * Note that update_relax_domain_level() in cpuset-v1.c can still call
 * rebuild_sched_domains_locked() directly without using this flag.
 */
static bool force_sd_rebuild;			/* RWCS */

/*
 * Partition root states:
 *
 *   0 - member (not a partition root)
 *   1 - partition root
 *   2 - partition root without load balancing (isolated)
 *  -1 - invalid partition root
 *  -2 - invalid isolated partition root
 *
 *  There are 2 types of partitions - local or remote. Local partitions are
 *  those whose parents are partition root themselves. Setting of
 *  cpuset.cpus.exclusive are optional in setting up local partitions.
 *  Remote partitions are those whose parents are not partition roots. Passing
 *  down exclusive CPUs by setting cpuset.cpus.exclusive along its ancestor
 *  nodes are mandatory in creating a remote partition.
 *
 *  For simplicity, a local partition can be created under a local or remote
 *  partition but a remote partition cannot have any partition root in its
 *  ancestor chain except the cgroup root.
 *
 *  A valid partition can be formed by setting exclusive_cpus or cpus_allowed
 *  if exclusive_cpus is not set. In the case of partition with empty
 *  exclusive_cpus, all the conflicting exclusive CPUs specified in the
 *  following cpumasks of sibling cpusets will be removed from its
 *  cpus_allowed in determining its effective_xcpus.
 *  - effective_xcpus
 *  - exclusive_cpus
 *
 *  The "cpuset.cpus.exclusive" control file should be used for setting up
 *  partition if the users want to get as many CPUs as possible.
 */
#define PRS_MEMBER		0
#define PRS_ROOT		1
#define PRS_ISOLATED		2
#define PRS_INVALID_ROOT	-1
#define PRS_INVALID_ISOLATED	-2

/*
 * Temporary cpumasks for working with partitions that are passed among
 * functions to avoid memory allocation in inner functions.
 */
struct tmpmasks {
	cpumask_var_t addmask, delmask;	/* For partition root */
	cpumask_var_t new_cpus;		/* For update_cpumasks_hier() */
};

void inc_dl_tasks_cs(struct task_struct *p)
{
	struct cpuset *cs = task_cs(p);

	atomic_inc(&cs->nr_deadline_tasks);
}

void dec_dl_tasks_cs(struct task_struct *p)
{
	struct cpuset *cs = task_cs(p);

	atomic_dec(&cs->nr_deadline_tasks);
}

static inline bool is_partition_valid(const struct cpuset *cs)
{
	return cs->partition_root_state > 0;
}

static inline bool is_partition_invalid(const struct cpuset *cs)
{
	return cs->partition_root_state < 0;
}

static inline bool cs_is_member(const struct cpuset *cs)
{
	return cs->partition_root_state == PRS_MEMBER;
}

/*
 * Callers should hold callback_lock to modify partition_root_state.
 */
static inline void make_partition_invalid(struct cpuset *cs)
{
	if (cs->partition_root_state > 0)
		cs->partition_root_state = -cs->partition_root_state;
}

/*
 * Send notification event of whenever partition_root_state changes.
 */
static inline void notify_partition_change(struct cpuset *cs, int old_prs)
{
	if (old_prs == cs->partition_root_state)
		return;
	cgroup_file_notify(&cs->partition_file);

	/* Reset prs_err if not invalid */
	if (is_partition_valid(cs))
		WRITE_ONCE(cs->prs_err, PERR_NONE);
}

/*
 * The top_cpuset is always synchronized to cpu_active_mask and we should avoid
 * using cpu_online_mask as much as possible. An active CPU is always an online
 * CPU, but not vice versa. cpu_active_mask and cpu_online_mask can differ
 * during hotplug operations. A CPU is marked active at the last stage of CPU
 * bringup (CPUHP_AP_ACTIVE). It is also the stage where cpuset hotplug code
 * will be called to update the sched domains so that the scheduler can move
 * a normal task to a newly active CPU or remove tasks away from a newly
 * inactivated CPU. The online bit is set much earlier in the CPU bringup
 * process and cleared much later in CPU teardown.
 *
 * If cpu_online_mask is used while a hotunplug operation is happening in
 * parallel, we may leave an offline CPU in cpu_allowed or some other masks.
 */
struct cpuset top_cpuset = {
	.flags = BIT(CS_CPU_EXCLUSIVE) |
		 BIT(CS_MEM_EXCLUSIVE) | BIT(CS_SCHED_LOAD_BALANCE),
	.partition_root_state = PRS_ROOT,
	.dl_bw_cpu = -1,
};

/**
 * cpuset_lock - Acquire the global cpuset mutex
 *
 * This locks the global cpuset mutex to prevent modifications to cpuset
 * hierarchy and configurations. This helper is not enough to make modification.
 */
void cpuset_lock(void)
{
	mutex_lock(&cpuset_mutex);
}

void cpuset_unlock(void)
{
	mutex_unlock(&cpuset_mutex);
}

void lockdep_assert_cpuset_lock_held(void)
{
	lockdep_assert_held(&cpuset_mutex);
}

/**
 * cpuset_full_lock - Acquire full protection for cpuset modification
 *
 * Takes both CPU hotplug read lock (cpus_read_lock()) and cpuset mutex
 * to safely modify cpuset data.
 */
void cpuset_full_lock(void)
{
	mutex_lock(&cpuset_top_mutex);
	cpus_read_lock();
	mutex_lock(&cpuset_mutex);
}

void cpuset_full_unlock(void)
{
	mutex_unlock(&cpuset_mutex);
	cpus_read_unlock();
	mutex_unlock(&cpuset_top_mutex);
}

#ifdef CONFIG_LOCKDEP
bool lockdep_is_cpuset_held(void)
{
	return lockdep_is_held(&cpuset_mutex) ||
	       lockdep_is_held(&cpuset_top_mutex);
}
#endif

static DEFINE_SPINLOCK(callback_lock);

void cpuset_callback_lock_irq(void)
{
	spin_lock_irq(&callback_lock);
}

void cpuset_callback_unlock_irq(void)
{
	spin_unlock_irq(&callback_lock);
}

static struct workqueue_struct *cpuset_migrate_mm_wq;

static DECLARE_WAIT_QUEUE_HEAD(cpuset_attach_wq);

/*
 * Cpuset task attach context
 * Protected by cpuset_mutex
 */
static struct {
	int in_progress;
	bool cpus_updated;
	bool mems_updated;
	bool task_work_queued;
	bool many_dest_cs;	/* Have many destination cpusets */
	struct cpuset *old_cs;	/* Source cpuset */
	nodemask_t nodemask_to;
} attach_ctx;
static LLIST_HEAD(src_cs_head);
static LLIST_HEAD(dst_cs_head);

/*
 * Wait if task attach is in progress until it is done and then acquire
 * cpuset_mutex before returning.
 */
static void wait_attach_done_lock(void)
	    __acquires(&cpuset_mutex)
{
	for (;;) {
		mutex_lock(&cpuset_mutex);
		if (!attach_ctx.in_progress)
			return;

		mutex_unlock(&cpuset_mutex);

		/* Wait until attach operation is done to prevent racing */
		wait_event(cpuset_attach_wq, attach_ctx.in_progress == 0);
	}
}

static inline void check_insane_mems_config(nodemask_t *nodes)
{
	if (!cpusets_insane_config() &&
		movable_only_nodes(nodes)) {
		static_branch_enable_cpuslocked(&cpusets_insane_config_key);
		pr_info("Unsupported (movable nodes only) cpuset configuration detected (nmask=%*pbl)!\n"
			"Cpuset allocations might fail even with a lot of memory available.\n",
			nodemask_pr_args(nodes));
	}
}

/*
 * decrease attach_ctx.in_progress.
 * wake_up cpuset_attach_wq if attach_ctx.in_progress==0.
 */
static inline void dec_attach_in_progress_locked(void)
{
	lockdep_assert_cpuset_lock_held();

	attach_ctx.in_progress--;
	if (!attach_ctx.in_progress)
		wake_up(&cpuset_attach_wq);
}

static inline void dec_attach_in_progress(void)
{
	mutex_lock(&cpuset_mutex);
	dec_attach_in_progress_locked();
	mutex_unlock(&cpuset_mutex);
}

static inline bool cpuset_v2(void)
{
	return !IS_ENABLED(CONFIG_CPUSETS_V1) ||
		cgroup_subsys_on_dfl(cpuset_cgrp_subsys);
}

/*
 * Cgroup v2 behavior is used on the "cpus" and "mems" control files when
 * on default hierarchy or when the cpuset_v2_mode flag is set by mounting
 * the v1 cpuset cgroup filesystem with the "cpuset_v2_mode" mount option.
 * With v2 behavior, "cpus" and "mems" are always what the users have
 * requested and won't be changed by hotplug events. Only the effective
 * cpus or mems will be affected.
 */
static inline bool is_in_v2_mode(void)
{
	return cpuset_v2() ||
	      (cpuset_cgrp_subsys.root->flags & CGRP_ROOT_CPUSET_V2_MODE);
}

/**
 * partition_is_populated - check if partition has tasks
 * @cs: partition root to be checked
 * @excluded_child: a child cpuset to be excluded in task checking
 * Return: true if there are tasks, false otherwise
 *
 * @cs should be a valid partition root or going to become a partition root.
 * @excluded_child should be non-NULL when this cpuset is going to become a
 * partition itself.
 *
 * Note that a remote partition is not allowed underneath a valid local
 * or remote partition. So if a non-partition root child is populated,
 * the whole partition is considered populated.
 */
static inline bool partition_is_populated(struct cpuset *cs,
					  struct cpuset *excluded_child)
{
	struct cpuset *cp;
	struct cgroup_subsys_state *pos_css;

	/*
	 * We cannot call cs_is_populated(cs) directly, as
	 * nr_populated_domain_children may include populated
	 * csets from descendants that are partitions.
	 */
	if (cgroup_has_tasks(cs->css.cgroup))
		return true;

	rcu_read_lock();
	cpuset_for_each_descendant_pre(cp, pos_css, cs) {
		if (cp == cs || cp == excluded_child)
			continue;

		if (is_partition_valid(cp)) {
			pos_css = css_rightmost_descendant(pos_css);
			continue;
		}

		if (cpuset_is_populated(cp)) {
			rcu_read_unlock();
			return true;
		}
	}
	rcu_read_unlock();
	return false;
}

/*
 * Return in pmask the portion of a task's cpusets's cpus_allowed that
 * are online and are capable of running the task.  If none are found,
 * walk up the cpuset hierarchy until we find one that does have some
 * appropriate cpus.
 *
 * One way or another, we guarantee to return some non-empty subset
 * of cpu_active_mask.
 *
 * Call with callback_lock or cpuset_mutex held.
 */
static void guarantee_active_cpus(struct task_struct *tsk,
				  struct cpumask *pmask)
{
	const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
	struct cpuset *cs;

	if (WARN_ON(!cpumask_and(pmask, possible_mask, cpu_active_mask)))
		cpumask_copy(pmask, cpu_active_mask);

	rcu_read_lock();
	cs = task_cs(tsk);

	while (!cpumask_intersects(cs->effective_cpus, pmask))
		cs = parent_cs(cs);

	cpumask_and(pmask, pmask, cs->effective_cpus);
	rcu_read_unlock();
}

/*
 * Return in *pmask the portion of a cpusets's mems_allowed that
 * are online, with memory.  If none are online with memory, walk
 * up the cpuset hierarchy until we find one that does have some
 * online mems.  The top cpuset always has some mems online. With v2,
 * effective_mems should always contain online memory nodes except
 * during the transition period where a memory node hotunplug operation
 * is in progress.
 *
 * One way or another, we guarantee to return some non-empty subset
 * of node_states[N_MEMORY].
 *
 * Call with callback_lock or cpuset_mutex held.
 */
static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
{
	while (!nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY]))
		cs = parent_cs(cs);
}

/**
 * alloc_cpumasks - Allocate an array of cpumask variables
 * @pmasks: Pointer to array of cpumask_var_t pointers
 * @size: Number of cpumasks to allocate
 * Return: 0 if successful, -ENOMEM otherwise.
 *
 * Allocates @size cpumasks and initializes them to empty. Returns 0 on
 * success, -ENOMEM on allocation failure. On failure, any previously
 * allocated cpumasks are freed.
 */
static inline int alloc_cpumasks(cpumask_var_t *pmasks[], u32 size)
{
	int i;

	for (i = 0; i < size; i++) {
		if (!zalloc_cpumask_var(pmasks[i], GFP_KERNEL)) {
			while (--i >= 0)
				free_cpumask_var(*pmasks[i]);
			return -ENOMEM;
		}
	}
	return 0;
}

/**
 * alloc_tmpmasks - Allocate temporary cpumasks for cpuset operations.
 * @tmp: Pointer to tmpmasks structure to populate
 * Return: 0 on success, -ENOMEM on allocation failure
 */
static inline int alloc_tmpmasks(struct tmpmasks *tmp)
{
	/*
	 * Array of pointers to the three cpumask_var_t fields in tmpmasks.
	 * Note: Array size must match actual number of masks (3)
	 */
	cpumask_var_t *pmask[3] = {
		&tmp->new_cpus,
		&tmp->addmask,
		&tmp->delmask
	};

	return alloc_cpumasks(pmask, ARRAY_SIZE(pmask));
}

/**
 * free_tmpmasks - free cpumasks in a tmpmasks structure
 * @tmp: the tmpmasks structure pointer
 */
static inline void free_tmpmasks(struct tmpmasks *tmp)
{
	if (!tmp)
		return;

	free_cpumask_var(tmp->new_cpus);
	free_cpumask_var(tmp->addmask);
	free_cpumask_var(tmp->delmask);
}

/**
 * dup_or_alloc_cpuset - Duplicate or allocate a new cpuset
 * @cs: Source cpuset to duplicate (NULL for a fresh allocation)
 *
 * Creates a new cpuset by either:
 * 1. Duplicating an existing cpuset (if @cs is non-NULL), or
 * 2. Allocating a fresh cpuset with zero-initialized masks (if @cs is NULL)
 *
 * Return: Pointer to newly allocated cpuset on success, NULL on failure
 */
static struct cpuset *dup_or_alloc_cpuset(struct cpuset *cs)
{
	struct cpuset *trial;

	/* Allocate base structure */
	trial = cs ? kmemdup(cs, sizeof(*cs), GFP_KERNEL) :
		     kzalloc_obj(*cs);
	if (!trial)
		return NULL;

	trial->dl_bw_cpu = -1;
	init_llist_node(&trial->attach_node);

	/* Setup cpumask pointer array */
	cpumask_var_t *pmask[4] = {
		&trial->cpus_allowed,
		&trial->effective_cpus,
		&trial->effective_xcpus,
		&trial->exclusive_cpus
	};

	if (alloc_cpumasks(pmask, ARRAY_SIZE(pmask))) {
		kfree(trial);
		return NULL;
	}

	/* Copy masks if duplicating */
	if (cs) {
		cpumask_copy(trial->cpus_allowed, cs->cpus_allowed);
		cpumask_copy(trial->effective_cpus, cs->effective_cpus);
		cpumask_copy(trial->effective_xcpus, cs->effective_xcpus);
		cpumask_copy(trial->exclusive_cpus, cs->exclusive_cpus);
	}

	return trial;
}

/**
 * free_cpuset - free the cpuset
 * @cs: the cpuset to be freed
 */
static inline void free_cpuset(struct cpuset *cs)
{
	free_cpumask_var(cs->cpus_allowed);
	free_cpumask_var(cs->effective_cpus);
	free_cpumask_var(cs->effective_xcpus);
	free_cpumask_var(cs->exclusive_cpus);
	kfree(cs);
}

/* Return user specified exclusive CPUs */
static inline struct cpumask *user_xcpus(struct cpuset *cs)
{
	return cpumask_empty(cs->exclusive_cpus) ? cs->cpus_allowed
						 : cs->exclusive_cpus;
}

static inline bool xcpus_empty(struct cpuset *cs)
{
	return cpumask_empty(cs->cpus_allowed) &&
	       cpumask_empty(cs->exclusive_cpus);
}

/*
 * cpusets_are_exclusive() - check if two cpusets are exclusive
 *
 * Return true if exclusive, false if not
 */
static inline bool cpusets_are_exclusive(struct cpuset *cs1, struct cpuset *cs2)
{
	struct cpumask *xcpus1 = user_xcpus(cs1);
	struct cpumask *xcpus2 = user_xcpus(cs2);

	if (cpumask_intersects(xcpus1, xcpus2))
		return false;
	return true;
}

/**
 * cpus_excl_conflict - Check if two cpusets have exclusive CPU conflicts
 * @trial:	the trial cpuset to be checked
 * @sibling:	a sibling cpuset to be checked against
 * @xcpus_changed: set if exclusive_cpus has been set
 *
 * Returns: true if CPU exclusivity conflict exists, false otherwise
 *
 * Conflict detection rules:
 *  o cgroup v1
 *    See cpuset1_cpus_excl_conflict()
 *  o cgroup v2
 *    - The exclusive_cpus values cannot overlap.
 *    - New exclusive_cpus cannot be a superset of a sibling's cpus_allowed.
 */
static inline bool cpus_excl_conflict(struct cpuset *trial, struct cpuset *sibling,
				      bool xcpus_changed)
{
	if (!cpuset_v2())
		return cpuset1_cpus_excl_conflict(trial, sibling);

	/* The cpus_allowed of a sibling cpuset cannot be a subset of the new exclusive_cpus */
	if (xcpus_changed && !cpumask_empty(sibling->cpus_allowed) &&
	    cpumask_subset(sibling->cpus_allowed, trial->exclusive_cpus))
		return true;

	/* Exclusive_cpus cannot intersect */
	return cpumask_intersects(trial->exclusive_cpus, sibling->exclusive_cpus);
}

static inline bool mems_excl_conflict(struct cpuset *cs1, struct cpuset *cs2)
{
	if ((is_mem_exclusive(cs1) || is_mem_exclusive(cs2)))
		return nodes_intersects(cs1->mems_allowed, cs2->mems_allowed);
	return false;
}

/*
 * validate_change() - Used to validate that any proposed cpuset change
 *		       follows the structural rules for cpusets.
 *
 * If we replaced the flag and mask values of the current cpuset
 * (cur) with those values in the trial cpuset (trial), would
 * our various subset and exclusive rules still be valid?  Presumes
 * cpuset_mutex held.
 *
 * 'cur' is the address of an actual, in-use cpuset.  Operations
 * such as list traversal that depend on the actual address of the
 * cpuset in the list must use cur below, not trial.
 *
 * 'trial' is the address of bulk structure copy of cur, with
 * perhaps one or more of the fields cpus_allowed, mems_allowed,
 * or flags changed to new, trial values.
 *
 * Return 0 if valid, -errno if not.
 */

static int validate_change(struct cpuset *cur, struct cpuset *trial)
{
	struct cgroup_subsys_state *css;
	struct cpuset *c, *par;
	bool xcpus_changed;
	int ret = 0;

	rcu_read_lock();

	if (!is_in_v2_mode())
		ret = cpuset1_validate_change(cur, trial);
	if (ret)
		goto out;

	/* Remaining checks don't apply to root cpuset */
	if (cur == &top_cpuset)
		goto out;

	par = parent_cs(cur);

	/*
	 * We can't shrink if we won't have enough room for SCHED_DEADLINE
	 * tasks. This check is not done when scheduling is disabled as the
	 * users should know what they are doing.
	 *
	 * For v1, effective_cpus == cpus_allowed & user_xcpus() returns
	 * cpus_allowed.
	 *
	 * For v2, is_cpu_exclusive() & is_sched_load_balance() are true only
	 * for non-isolated partition root. At this point, the target
	 * effective_cpus isn't computed yet. user_xcpus() is the best
	 * approximation.
	 *
	 * TBD: May need to precompute the real effective_cpus here in case
	 * incorrect scheduling of SCHED_DEADLINE tasks in a partition
	 * becomes an issue.
	 */
	ret = -EBUSY;
	if (is_cpu_exclusive(cur) && is_sched_load_balance(cur) &&
	    !cpuset_cpumask_can_shrink(cur->effective_cpus, user_xcpus(trial)))
		goto out;

	/*
	 * If either I or some sibling (!= me) is exclusive, we can't
	 * overlap. exclusive_cpus cannot overlap with each other if set.
	 */
	ret = -EINVAL;
	xcpus_changed = !cpumask_equal(cur->exclusive_cpus, trial->exclusive_cpus);
	cpuset_for_each_child(c, css, par) {
		if (c == cur)
			continue;
		if (cpus_excl_conflict(trial, c, xcpus_changed))
			goto out;
		if (mems_excl_conflict(trial, c))
			goto out;
	}

	ret = 0;
out:
	rcu_read_unlock();
	return ret;
}

#ifdef CONFIG_SMP

/*
 * generate_sched_domains()
 *
 * This function builds a partial partition of the systems CPUs
 * A 'partial partition' is a set of non-overlapping subsets whose
 * union is a subset of that set.
 * The output of this function needs to be passed to kernel/sched/core.c
 * partition_sched_domains() routine, which will rebuild the scheduler's
 * load balancing domains (sched domains) as specified by that partial
 * partition.
 *
 * See "What is sched_load_balance" in Documentation/admin-guide/cgroup-v1/cpusets.rst
 * for a background explanation of this.
 *
 * Does not return errors, on the theory that the callers of this
 * routine would rather not worry about failures to rebuild sched
 * domains when operating in the severe memory shortage situations
 * that could cause allocation failures below.
 *
 * Must be called with cpuset_mutex held.
 *
 * The three key local variables below are:
 *    cp - cpuset pointer, used (together with pos_css) to perform a
 *	   top-down scan of all cpusets. For our purposes, rebuilding
 *	   the schedulers sched domains, we can ignore !is_sched_load_
 *	   balance cpusets.
 *  csa  - (for CpuSet Array) Array of pointers to all the cpusets
 *	   that need to be load balanced, for convenient iterative
 *	   access by the subsequent code that finds the best partition,
 *	   i.e the set of domains (subsets) of CPUs such that the
 *	   cpus_allowed of every cpuset marked is_sched_load_balance
 *	   is a subset of one of these domains, while there are as
 *	   many such domains as possible, each as small as possible.
 * doms  - Conversion of 'csa' to an array of cpumasks, for passing to
 *	   the kernel/sched/core.c routine partition_sched_domains() in a
 *	   convenient format, that can be easily compared to the prior
 *	   value to determine what partition elements (sched domains)
 *	   were changed (added or removed.)
 */
static int generate_sched_domains(cpumask_var_t **domains,
			struct sched_domain_attr **attributes)
{
	struct cpuset *cp;	/* top-down scan of cpusets */
	struct cpuset **csa;	/* array of all cpuset ptrs */
	int i, j;		/* indices for partition finding loops */
	cpumask_var_t *doms;	/* resulting partition; i.e. sched domains */
	struct sched_domain_attr *dattr;  /* attributes for custom domains */
	int ndoms = 0;		/* number of sched domains in result */
	struct cgroup_subsys_state *pos_css;

	if (!cpuset_v2())
		return cpuset1_generate_sched_domains(domains, attributes);

	doms = NULL;
	dattr = NULL;
	csa = NULL;

	/* Special case for the 99% of systems with one, full, sched domain */
	if (cpumask_empty(subpartitions_cpus)) {
		ndoms = 1;
		/* !csa will be checked and can be correctly handled */
		goto generate_doms;
	}

	csa = kmalloc_objs(cp, nr_cpusets());
	if (!csa)
		goto done;

	/* Find how many partitions and cache them to csa[] */
	rcu_read_lock();
	cpuset_for_each_descendant_pre(cp, pos_css, &top_cpuset) {
		/*
		 * Only valid partition roots that are not isolated and with
		 * non-empty effective_cpus will be saved into csa[].
		 */
		if ((cp->partition_root_state == PRS_ROOT) &&
		    !cpumask_empty(cp->effective_cpus))
			csa[ndoms++] = cp;

		/*
		 * Skip @cp's subtree if not a partition root and has no
		 * exclusive CPUs to be granted to child cpusets.
		 */
		if (!is_partition_valid(cp) && cpumask_empty(cp->exclusive_cpus))
			pos_css = css_rightmost_descendant(pos_css);
	}
	rcu_read_unlock();

	for (i = 0; i < ndoms; i++) {
		for (j = i + 1; j < ndoms; j++) {
			if (cpusets_overlap(csa[i], csa[j]))
				/*
				 * Cgroup v2 shouldn't pass down overlapping
				 * partition root cpusets.
				 */
				WARN_ON_ONCE(1);
		}
	}

generate_doms:
	doms = alloc_sched_domains(ndoms);
	if (!doms)
		goto done;

	/*
	 * The rest of the code, including the scheduler, can deal with
	 * dattr==NULL case. No need to abort if alloc fails.
	 */
	dattr = kmalloc_objs(struct sched_domain_attr, ndoms);

	/*
	 * Cgroup v2 doesn't support domain attributes, just set all of them
	 * to SD_ATTR_INIT. Also non-isolating partition root CPUs are a
	 * subset of HK_TYPE_DOMAIN_BOOT housekeeping CPUs.
	 */
	for (i = 0; i < ndoms; i++) {
		/*
		 * The top cpuset may contain some boot time isolated
		 * CPUs that need to be excluded from the sched domain.
		 */
		if (!csa || csa[i] == &top_cpuset)
			cpumask_and(doms[i], top_cpuset.effective_cpus,
				    housekeeping_cpumask(HK_TYPE_DOMAIN_BOOT));
		else
			cpumask_copy(doms[i], csa[i]->effective_cpus);
		if (dattr)
			dattr[i] = SD_ATTR_INIT;
	}

done:
	kfree(csa);

	/*
	 * Fallback to the default domain if kmalloc() failed.
	 * See comments in partition_sched_domains().
	 */
	if (doms == NULL)
		ndoms = 1;

	*domains    = doms;
	*attributes = dattr;
	return ndoms;
}

static void dl_update_tasks_root_domain(struct cpuset *cs)
{
	struct css_task_iter it;
	struct task_struct *task;

	if (atomic_read(&cs->nr_deadline_tasks) == 0)
		return;

	css_task_iter_start(&cs->css, 0, &it);

	while ((task = css_task_iter_next(&it)))
		dl_add_task_root_domain(task);

	css_task_iter_end(&it);
}

void dl_rebuild_rd_accounting(void)
{
	struct cpuset *cs = NULL;
	struct cgroup_subsys_state *pos_css;
	int cpu;
	u64 cookie = ++dl_cookie;

	lockdep_assert_cpuset_lock_held();
	lockdep_assert_cpus_held();
	lockdep_assert_held(&sched_domains_mutex);

	rcu_read_lock();

	for_each_possible_cpu(cpu) {
		if (dl_bw_visited(cpu, cookie))
			continue;

		dl_clear_root_domain_cpu(cpu);
	}

	cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {

		if (cpumask_empty(cs->effective_cpus)) {
			pos_css = css_rightmost_descendant(pos_css);
			continue;
		}

		css_get(&cs->css);

		rcu_read_unlock();

		dl_update_tasks_root_domain(cs);

		rcu_read_lock();
		css_put(&cs->css);
	}
	rcu_read_unlock();
}

/*
 * Rebuild scheduler domains.
 *
 * If the flag 'sched_load_balance' of any cpuset with non-empty
 * 'cpus' changes, or if the 'cpus' allowed changes in any cpuset
 * which has that flag enabled, or if any cpuset with a non-empty
 * 'cpus' is removed, then call this routine to rebuild the
 * scheduler's dynamic sched domains.
 *
 * Call with cpuset_mutex held.  Takes cpus_read_lock().
 */
void rebuild_sched_domains_locked(void)
{
	struct sched_domain_attr *attr;
	cpumask_var_t *doms;
	int ndoms;
	int i;

	lockdep_assert_cpus_held();
	lockdep_assert_cpuset_lock_held();
	force_sd_rebuild = false;

	/* Generate domain masks and attrs */
	ndoms = generate_sched_domains(&doms, &attr);

	/*
	* cpuset_hotplug_workfn is invoked synchronously now, thus this
	* function should not race with CPU hotplug. And the effective CPUs
	* must not include any offline CPUs. Passing an offline CPU in the
	* doms to partition_sched_domains() will trigger a kernel panic.
	*
	* We perform a final check here: if the doms contains any
	* offline CPUs, a warning is emitted and we return directly to
	* prevent the panic.
	*/
	for (i = 0; doms && i < ndoms; i++) {
		if (WARN_ON_ONCE(!cpumask_subset(doms[i], cpu_active_mask))) {
			free_sched_domains(doms, ndoms);
			kfree(attr);
			return;
		}
	}

	/* Have scheduler rebuild the domains */
	partition_sched_domains(ndoms, doms, attr);
}
#else /* !CONFIG_SMP */
void rebuild_sched_domains_locked(void)
{
}
#endif /* CONFIG_SMP */

static void rebuild_sched_domains_cpuslocked(void)
{
	mutex_lock(&cpuset_mutex);
	rebuild_sched_domains_locked();
	mutex_unlock(&cpuset_mutex);
}

void rebuild_sched_domains(void)
{
	cpus_read_lock();
	rebuild_sched_domains_cpuslocked();
	cpus_read_unlock();
}

void cpuset_reset_sched_domains(void)
{
	mutex_lock(&cpuset_mutex);
	partition_sched_domains(1, NULL, NULL);
	mutex_unlock(&cpuset_mutex);
}

/**
 * cpuset_update_tasks_cpumask - Update the cpumasks of tasks in the cpuset.
 * @cs: the cpuset in which each task's cpus_allowed mask needs to be changed
 * @new_cpus: the temp variable for the new effective_cpus mask
 *
 * Iterate through each task of @cs updating its cpus_allowed to the
 * effective cpuset's.  As this function is called with cpuset_mutex held,
 * cpuset membership stays stable.
 *
 * For top_cpuset, task_cpu_possible_mask() is used instead of effective_cpus
 * to make sure all offline CPUs are also included as hotplug code won't
 * update cpumasks for tasks in top_cpuset.
 *
 * As task_cpu_possible_mask() can be task dependent in arm64, we have to
 * do cpu masking per task instead of doing it once for all.
 */
void cpuset_update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus)
{
	struct css_task_iter it;
	struct task_struct *task;
	bool top_cs = cs == &top_cpuset;

	css_task_iter_start(&cs->css, 0, &it);
	while ((task = css_task_iter_next(&it))) {
		const struct cpumask *possible_mask = task_cpu_possible_mask(task);

		if (top_cs) {
			/*
			 * PF_KTHREAD tasks are handled by housekeeping.
			 * PF_NO_SETAFFINITY tasks are ignored.
			 */
			if (task->flags & (PF_KTHREAD | PF_NO_SETAFFINITY))
				continue;
			cpumask_andnot(new_cpus, possible_mask, subpartitions_cpus);
		} else {
			cpumask_and(new_cpus, possible_mask, cs->effective_cpus);
		}
		set_cpus_allowed_ptr(task, new_cpus);
	}
	css_task_iter_end(&it);
}

/**
 * compute_effective_cpumask - Compute the effective cpumask of the cpuset
 * @new_cpus: the temp variable for the new effective_cpus mask
 * @cs: the cpuset the need to recompute the new effective_cpus mask
 * @parent: the parent cpuset
 *
 * For v2, the parent's effective_cpus is inherited if cpumask is empty.
 * The result is valid only if the given cpuset isn't a partition root.
 */
static void compute_effective_cpumask(struct cpumask *new_cpus,
				      struct cpuset *cs, struct cpuset *parent)
{
	bool has_cpus;

	has_cpus = cpumask_and(new_cpus, cs->cpus_allowed, parent->effective_cpus);
	if (!has_cpus && is_in_v2_mode())
		cpumask_copy(new_cpus, parent->effective_cpus);
}

/**
 * compute_effective_nodemask - Compute the effective nodemask of the cpuset
 * @new_mems: the temp variable for the new effective_mems mask
 * @cs: the cpuset the need to recompute the new effective_mems mask
 * @parent: the parent cpuset
 *
 * For v2, the parent's effective_mems is inherited if nodemask is empty.
 */
static void compute_effective_nodemask(nodemask_t *new_mems,
				       struct cpuset *cs, struct cpuset *parent)
{
	bool has_mems;

	has_mems = nodes_and(*new_mems, cs->mems_allowed, parent->effective_mems);
	if (!has_mems && is_in_v2_mode())
		nodes_copy(*new_mems, parent->effective_mems);
}

/*
 * Commands for update_parent_effective_cpumask
 */
enum partition_cmd {
	partcmd_enable,		/* Enable partition root	  */
	partcmd_enablei,	/* Enable isolated partition root */
	partcmd_disable,	/* Disable partition root	  */
	partcmd_update,		/* Update parent's effective_cpus */
	partcmd_invalidate,	/* Make partition invalid	  */
};

static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
				    struct tmpmasks *tmp);

/*
 * Update partition exclusive flag
 *
 * Return: 0 if successful, an error code otherwise
 */
static int update_partition_exclusive_flag(struct cpuset *cs, int new_prs)
{
	bool exclusive = (new_prs > PRS_MEMBER);

	if (exclusive && !is_cpu_exclusive(cs)) {
		if (cpuset_update_flag(CS_CPU_EXCLUSIVE, cs, 1))
			return PERR_NOTEXCL;
	} else if (!exclusive && is_cpu_exclusive(cs)) {
		/* Turning off CS_CPU_EXCLUSIVE will not return error */
		cpuset_update_flag(CS_CPU_EXCLUSIVE, cs, 0);
	}
	return 0;
}

/*
 * Update partition load balance flag and/or rebuild sched domain
 *
 * Changing load balance flag will automatically call
 * rebuild_sched_domains_locked().
 * This function is for cgroup v2 only.
 */
static void update_partition_sd_lb(struct cpuset *cs, int old_prs)
{
	int new_prs = cs->partition_root_state;
	bool rebuild_domains = (new_prs > 0) || (old_prs > 0);
	bool new_lb;

	/*
	 * If cs is not a valid partition root, the load balance state
	 * will follow its parent.
	 */
	if (new_prs > 0) {
		new_lb = (new_prs != PRS_ISOLATED);
	} else {
		new_lb = is_sched_load_balance(parent_cs(cs));
	}
	if (new_lb != !!is_sched_load_balance(cs)) {
		rebuild_domains = true;
		if (new_lb)
			set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
		else
			clear_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
	}

	if (rebuild_domains)
		cpuset_force_rebuild();
}

/*
 * tasks_nocpu_error - Return true if tasks will have no effective_cpus
 */
static bool tasks_nocpu_error(struct cpuset *parent, struct cpuset *cs,
			      struct cpumask *xcpus)
{
	/*
	 * A populated partition (cs or parent) can't have empty effective_cpus
	 */
	return (cpumask_subset(parent->effective_cpus, xcpus) &&
		partition_is_populated(parent, cs)) ||
	       (!cpumask_intersects(xcpus, cpu_active_mask) &&
		partition_is_populated(cs, NULL));
}

static void reset_partition_data(struct cpuset *cs)
{
	struct cpuset *parent = parent_cs(cs);

	if (!cpuset_v2())
		return;

	lockdep_assert_held(&callback_lock);

	if (cpumask_empty(cs->exclusive_cpus)) {
		cpumask_clear(cs->effective_xcpus);
		if (is_cpu_exclusive(cs))
			clear_bit(CS_CPU_EXCLUSIVE, &cs->flags);
	}
	if (!cpumask_and(cs->effective_cpus, parent->effective_cpus, cs->cpus_allowed))
		cpumask_copy(cs->effective_cpus, parent->effective_cpus);
}

/*
 * isolated_cpus_update - Update the isolated_cpus mask
 * @old_prs: old partition_root_state
 * @new_prs: new partition_root_state
 * @xcpus: exclusive CPUs with state change
 */
static void isolated_cpus_update(int old_prs, int new_prs, struct cpumask *xcpus)
{
	WARN_ON_ONCE(old_prs == new_prs);
	lockdep_assert_held(&callback_lock);
	lockdep_assert_held(&cpuset_mutex);
	if (new_prs == PRS_ISOLATED) {
		if (cpumask_subset(xcpus, isolated_cpus))
			return;
		cpumask_or(isolated_cpus, isolated_cpus, xcpus);
	} else {
		if (!cpumask_intersects(xcpus, isolated_cpus))
			return;
		cpumask_andnot(isolated_cpus, isolated_cpus, xcpus);
	}
	update_housekeeping = true;
}

/*
 * partition_xcpus_add - Add new exclusive CPUs to partition
 * @new_prs: new partition_root_state
 * @parent: parent cpuset
 * @xcpus: exclusive CPUs to be added
 *
 * Remote partition if parent == NULL
 */
static void partition_xcpus_add(int new_prs, struct cpuset *parent,
				struct cpumask *xcpus)
{
	WARN_ON_ONCE(new_prs < 0);
	lockdep_assert_held(&callback_lock);
	if (!parent)
		parent = &top_cpuset;


	if (parent == &top_cpuset)
		cpumask_or(subpartitions_cpus, subpartitions_cpus, xcpus);

	if (new_prs != parent->partition_root_state)
		isolated_cpus_update(parent->partition_root_state, new_prs,
				     xcpus);

	cpumask_andnot(parent->effective_cpus, parent->effective_cpus, xcpus);
}

/*
 * partition_xcpus_del - Remove exclusive CPUs from partition
 * @old_prs: old partition_root_state
 * @parent: parent cpuset
 * @xcpus: exclusive CPUs to be removed
 *
 * Remote partition if parent == NULL
 */
static void partition_xcpus_del(int old_prs, struct cpuset *parent,
				struct cpumask *xcpus)
{
	WARN_ON_ONCE(old_prs < 0);
	lockdep_assert_held(&callback_lock);
	if (!parent)
		parent = &top_cpuset;

	if (parent == &top_cpuset)
		cpumask_andnot(subpartitions_cpus, subpartitions_cpus, xcpus);

	if (old_prs != parent->partition_root_state)
		isolated_cpus_update(old_prs, parent->partition_root_state,
				     xcpus);

	cpumask_or(parent->effective_cpus, parent->effective_cpus, xcpus);
	cpumask_and(parent->effective_cpus, parent->effective_cpus, cpu_active_mask);
}

/*
 * isolated_cpus_can_update - check for isolated & nohz_full conflicts
 * @add_cpus: cpu mask for cpus that are going to be isolated
 * @del_cpus: cpu mask for cpus that are no longer isolated, can be NULL
 * Return: false if there is conflict, true otherwise
 *
 * If nohz_full is enabled and we have isolated CPUs, their combination must
 * still leave housekeeping CPUs.
 *
 * TBD: Should consider merging this function into
 *      prstate_housekeeping_conflict().
 */
static bool isolated_cpus_can_update(struct cpumask *add_cpus,
				     struct cpumask *del_cpus)
{
	cpumask_var_t full_hk_cpus;
	int res = true;

	if (!housekeeping_enabled(HK_TYPE_KERNEL_NOISE))
		return true;

	if (del_cpus && cpumask_weight_and(del_cpus,
			housekeeping_cpumask(HK_TYPE_KERNEL_NOISE)))
		return true;

	if (!alloc_cpumask_var(&full_hk_cpus, GFP_KERNEL))
		return false;

	cpumask_and(full_hk_cpus, housekeeping_cpumask(HK_TYPE_KERNEL_NOISE),
		    housekeeping_cpumask(HK_TYPE_DOMAIN));
	cpumask_andnot(full_hk_cpus, full_hk_cpus, isolated_cpus);
	cpumask_and(full_hk_cpus, full_hk_cpus, cpu_active_mask);
	if (!cpumask_weight_andnot(full_hk_cpus, add_cpus))
		res = false;

	free_cpumask_var(full_hk_cpus);
	return res;
}

/*
 * prstate_housekeeping_conflict - check for partition & housekeeping conflicts
 * @prstate: partition root state to be checked
 * @new_cpus: cpu mask
 * Return: true if there is conflict, false otherwise
 *
 * CPUs outside of HK_TYPE_DOMAIN_BOOT, if defined, can only be used in an
 * isolated partition.
 */
static bool prstate_housekeeping_conflict(int prstate, struct cpumask *new_cpus)
{
	if (!housekeeping_enabled(HK_TYPE_DOMAIN_BOOT))
		return false;

	if ((prstate != PRS_ISOLATED) &&
	    !cpumask_subset(new_cpus, housekeeping_cpumask(HK_TYPE_DOMAIN_BOOT)))
		return true;

	return false;
}

/*
 * cpuset_update_sd_hk_unlock - Rebuild sched domains, update HK & unlock
 *
 * Update housekeeping cpumasks and rebuild sched domains if necessary and
 * then do a cpuset_full_unlock().
 * This should be called at the end of cpuset operation.
 */
static void cpuset_update_sd_hk_unlock(void)
	__releases(&cpuset_mutex)
	__releases(&cpuset_top_mutex)
{
	/* force_sd_rebuild will be cleared in rebuild_sched_domains_locked() */
	if (force_sd_rebuild)
		rebuild_sched_domains_locked();

	if (update_housekeeping) {
		update_housekeeping = false;
		cpumask_copy(isolated_hk_cpus, isolated_cpus);

		/*
		 * housekeeping_update() is now called without holding
		 * cpus_read_lock and cpuset_mutex. Only cpuset_top_mutex
		 * is still being held for mutual exclusion.
		 */
		mutex_unlock(&cpuset_mutex);
		cpus_read_unlock();
		WARN_ON_ONCE(housekeeping_update(isolated_hk_cpus));
		mutex_unlock(&cpuset_top_mutex);
	} else {
		cpuset_full_unlock();
	}
}

/*
 * Work function to invoke cpuset_update_sd_hk_unlock()
 */
static void hk_sd_workfn(struct work_struct *work)
{
	cpuset_full_lock();
	cpuset_update_sd_hk_unlock();
}

/**
 * rm_siblings_excl_cpus - Remove exclusive CPUs that are used by sibling cpusets
 * @parent: Parent cpuset containing all siblings
 * @cs: Current cpuset (will be skipped)
 * @excpus:  exclusive effective CPU mask to modify
 *
 * This function ensures the given @excpus mask doesn't include any CPUs that
 * are exclusively allocated to sibling cpusets. It walks through all siblings
 * of @cs under @parent and removes their exclusive CPUs from @excpus.
 */
static int rm_siblings_excl_cpus(struct cpuset *parent, struct cpuset *cs,
					struct cpumask *excpus)
{
	struct cgroup_subsys_state *css;
	struct cpuset *sibling;
	int retval = 0;

	if (cpumask_empty(excpus))
		return 0;

	/*
	 * Remove exclusive CPUs from siblings
	 */
	rcu_read_lock();
	cpuset_for_each_child(sibling, css, parent) {
		struct cpumask *sibling_xcpus;

		if (sibling == cs)
			continue;

		/*
		 * If exclusive_cpus is defined, effective_xcpus will always
		 * be a subset. Otherwise, effective_xcpus will only be set
		 * in a valid partition root.
		 */
		sibling_xcpus = cpumask_empty(sibling->exclusive_cpus)
			      ? sibling->effective_xcpus
			      : sibling->exclusive_cpus;

		if (cpumask_intersects(excpus, sibling_xcpus)) {
			cpumask_andnot(excpus, excpus, sibling_xcpus);
			retval++;
		}
	}
	rcu_read_unlock();

	return retval;
}

/*
 * compute_excpus - compute effective exclusive CPUs
 * @cs: cpuset
 * @xcpus: effective exclusive CPUs value to be set
 * Return: 0 if there is no sibling conflict, > 0 otherwise
 *
 * If exclusive_cpus isn't explicitly set , we have to scan the sibling cpusets
 * and exclude their exclusive_cpus or effective_xcpus as well.
 */
static int compute_excpus(struct cpuset *cs, struct cpumask *excpus)
{
	struct cpuset *parent = parent_cs(cs);

	cpumask_and(excpus, user_xcpus(cs), parent->effective_xcpus);

	if (!cpumask_empty(cs->exclusive_cpus))
		return 0;

	return rm_siblings_excl_cpus(parent, cs, excpus);
}

/*
 * compute_trialcs_excpus - Compute effective exclusive CPUs for a trial cpuset
 * @trialcs: The trial cpuset containing the proposed new configuration
 * @cs: The original cpuset that the trial configuration is based on
 * Return: 0 if successful with no sibling conflict, >0 if a conflict is found
 *
 * Computes the effective_xcpus for a trial configuration. @cs is provided to represent
 * the real cs.
 */
static int compute_trialcs_excpus(struct cpuset *trialcs, struct cpuset *cs)
{
	struct cpuset *parent = parent_cs(trialcs);
	struct cpumask *excpus = trialcs->effective_xcpus;

	/* trialcs is member, cpuset.cpus has no impact to excpus */
	if (cs_is_member(cs))
		cpumask_and(excpus, trialcs->exclusive_cpus,
				parent->effective_xcpus);
	else
		cpumask_and(excpus, user_xcpus(trialcs), parent->effective_xcpus);

	return rm_siblings_excl_cpus(parent, cs, excpus);
}

static inline bool is_remote_partition(struct cpuset *cs)
{
	return cs->remote_partition;
}

static inline bool is_local_partition(struct cpuset *cs)
{
	return is_partition_valid(cs) && !is_remote_partition(cs);
}

/*
 * remote_partition_enable - Enable current cpuset as a remote partition root
 * @cs: the cpuset to update
 * @new_prs: new partition_root_state
 * @tmp: temporary masks
 * Return: 0 if successful, errcode if error
 *
 * Enable the current cpuset to become a remote partition root taking CPUs
 * directly from the top cpuset. cpuset_mutex must be held by the caller.
 */
static int remote_partition_enable(struct cpuset *cs, int new_prs,
				   struct tmpmasks *tmp)
{
	/*
	 * The user must have sysadmin privilege.
	 */
	if (!capable(CAP_SYS_ADMIN))
		return PERR_ACCESS;

	/*
	 * The requested exclusive_cpus must not be allocated to other
	 * partitions and it can't use up all the root's effective_cpus.
	 *
	 * The effective_xcpus mask can contain offline CPUs, but there must
	 * be at least one or more online CPUs present before it can be enabled.
	 *
	 * Note that creating a remote partition with any local partition root
	 * above it or remote partition root underneath it is not allowed.
	 */
	compute_excpus(cs, tmp->new_cpus);
	WARN_ON_ONCE(cpumask_intersects(tmp->new_cpus, subpartitions_cpus));
	if (!cpumask_intersects(tmp->new_cpus, cpu_active_mask) ||
	    cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus))
		return PERR_INVCPUS;
	if (((new_prs == PRS_ISOLATED) &&
	     !isolated_cpus_can_update(tmp->new_cpus, NULL)) ||
	    prstate_housekeeping_conflict(new_prs, tmp->new_cpus))
		return PERR_HKEEPING;

	spin_lock_irq(&callback_lock);
	partition_xcpus_add(new_prs, NULL, tmp->new_cpus);
	cs->remote_partition = true;
	cpumask_copy(cs->effective_xcpus, tmp->new_cpus);
	spin_unlock_irq(&callback_lock);
	cpuset_force_rebuild();
	WRITE_ONCE(cs->prs_err, 0);

	/*
	 * Propagate changes in top_cpuset's effective_cpus down the hierarchy.
	 */
	cpuset_update_tasks_cpumask(&top_cpuset, tmp->new_cpus);
	update_sibling_cpumasks(&top_cpuset, NULL, tmp);
	return 0;
}

/*
 * remote_partition_disable - Remove current cpuset from remote partition list
 * @cs: the cpuset to update
 * @tmp: temporary masks
 *
 * The effective_cpus is also updated.
 *
 * cpuset_mutex must be held by the caller.
 */
static void remote_partition_disable(struct cpuset *cs, struct tmpmasks *tmp)
{
	WARN_ON_ONCE(!is_remote_partition(cs));
	/*
	 * When a CPU is offlined, top_cpuset may end up with no available CPUs,
	 * which should clear subpartitions_cpus. We should not emit a warning for this
	 * scenario: the hierarchy is updated from top to bottom, so subpartitions_cpus
	 * may already be cleared when disabling the partition.
	 */
	WARN_ON_ONCE(!cpumask_subset(cs->effective_xcpus, subpartitions_cpus) &&
		     !cpumask_empty(subpartitions_cpus));

	spin_lock_irq(&callback_lock);
	cs->remote_partition = false;
	partition_xcpus_del(cs->partition_root_state, NULL, cs->effective_xcpus);
	if (cs->prs_err)
		cs->partition_root_state = -cs->partition_root_state;
	else
		cs->partition_root_state = PRS_MEMBER;

	/* effective_xcpus may need to be changed */
	compute_excpus(cs, cs->effective_xcpus);
	reset_partition_data(cs);
	spin_unlock_irq(&callback_lock);
	cpuset_force_rebuild();

	/*
	 * Propagate changes in top_cpuset's effective_cpus down the hierarchy.
	 */
	cpuset_update_tasks_cpumask(&top_cpuset, tmp->new_cpus);
	update_sibling_cpumasks(&top_cpuset, NULL, tmp);
}

/*
 * remote_cpus_update - cpus_exclusive change of remote partition
 * @cs: the cpuset to be updated
 * @xcpus: the new exclusive_cpus mask, if non-NULL
 * @excpus: the new effective_xcpus mask
 * @tmp: temporary masks
 *
 * top_cpuset and subpartitions_cpus will be updated or partition can be
 * invalidated.
 */
static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus,
			       struct cpumask *excpus, struct tmpmasks *tmp)
{
	bool adding, deleting;
	int prs = cs->partition_root_state;

	if (WARN_ON_ONCE(!is_remote_partition(cs)))
		return;

	WARN_ON_ONCE(!cpumask_subset(cs->effective_xcpus, subpartitions_cpus));

	if (cpumask_empty(excpus)) {
		WRITE_ONCE(cs->prs_err, PERR_CPUSEMPTY);
		goto invalidate;
	}

	adding   = cpumask_andnot(tmp->addmask, excpus, cs->effective_xcpus);
	deleting = cpumask_andnot(tmp->delmask, cs->effective_xcpus, excpus);

	/*
	 * Additions of remote CPUs is only allowed if those CPUs are
	 * not allocated to other partitions and there are effective_cpus
	 * left in the top cpuset.
	 */
	if (adding) {
		WARN_ON_ONCE(cpumask_intersects(tmp->addmask, subpartitions_cpus));
		if (!capable(CAP_SYS_ADMIN))
			WRITE_ONCE(cs->prs_err, PERR_ACCESS);
		else if (cpumask_intersects(tmp->addmask, subpartitions_cpus) ||
			 cpumask_subset(top_cpuset.effective_cpus, tmp->addmask))
			WRITE_ONCE(cs->prs_err, PERR_NOCPUS);
		else if ((prs == PRS_ISOLATED) &&
			 !isolated_cpus_can_update(tmp->addmask, tmp->delmask))
			WRITE_ONCE(cs->prs_err, PERR_HKEEPING);
		if (cs->prs_err)
			goto invalidate;
	}

	spin_lock_irq(&callback_lock);
	if (adding)
		partition_xcpus_add(prs, NULL, tmp->addmask);
	if (deleting)
		partition_xcpus_del(prs, NULL, tmp->delmask);
	/*
	 * Need to update effective_xcpus and exclusive_cpus now as
	 * update_sibling_cpumasks() below may iterate back to the same cs.
	 */
	cpumask_copy(cs->effective_xcpus, excpus);
	if (xcpus)
		cpumask_copy(cs->exclusive_cpus, xcpus);
	spin_unlock_irq(&callback_lock);
	if (adding || deleting)
		cpuset_force_rebuild();

	/*
	 * Propagate changes in top_cpuset's effective_cpus down the hierarchy.
	 */
	cpuset_update_tasks_cpumask(&top_cpuset, tmp->new_cpus);
	update_sibling_cpumasks(&top_cpuset, NULL, tmp);
	return;

invalidate:
	remote_partition_disable(cs, tmp);
}

/**
 * update_parent_effective_cpumask - update effective_cpus mask of parent cpuset
 * @cs:      The cpuset that requests change in partition root state
 * @cmd:     Partition root state change command
 * @newmask: Optional new cpumask for partcmd_update
 * @tmp:     Temporary addmask and delmask
 * Return:   0 or a partition root state error code
 *
 * For partcmd_enable*, the cpuset is being transformed from a non-partition
 * root to a partition root. The effective_xcpus (cpus_allowed if
 * effective_xcpus not set) mask of the given cpuset will be taken away from
 * parent's effective_cpus. The function will return 0 if all the CPUs listed
 * in effective_xcpus can be granted or an error code will be returned.
 *
 * For partcmd_disable, the cpuset is being transformed from a partition
 * root back to a non-partition root. Any CPUs in effective_xcpus will be
 * given back to parent's effective_cpus. 0 will always be returned.
 *
 * For partcmd_update, if the optional newmask is specified, the cpu list is
 * to be changed from effective_xcpus to newmask. Otherwise, effective_xcpus is
 * assumed to remain the same. The cpuset should either be a valid or invalid
 * partition root. The partition root state may change from valid to invalid
 * or vice versa. An error code will be returned if transitioning from
 * invalid to valid violates the exclusivity rule.
 *
 * For partcmd_invalidate, the current partition will be made invalid.
 *
 * The partcmd_enable* and partcmd_disable commands are used by
 * update_prstate(). An error code may be returned and the caller will check
 * for error.
 *
 * The partcmd_update command is used by update_cpumasks_hier() with newmask
 * NULL and update_cpumask() with newmask set. The partcmd_invalidate is used
 * by update_cpumask() with NULL newmask. In both cases, the callers won't
 * check for error and so partition_root_state and prs_err will be updated
 * directly.
 */
static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
					   struct cpumask *newmask,
					   struct tmpmasks *tmp)
{
	struct cpuset *parent = parent_cs(cs);
	int adding;	/* Adding cpus to parent's effective_cpus	*/
	int deleting;	/* Deleting cpus from parent's effective_cpus	*/
	int old_prs, new_prs;
	int part_error = PERR_NONE;	/* Partition error? */
	struct cpumask *xcpus = user_xcpus(cs);
	int parent_prs = parent->partition_root_state;
	bool nocpu;

	lockdep_assert_cpuset_lock_held();
	WARN_ON_ONCE(is_remote_partition(cs));	/* For local partition only */

	/*
	 * new_prs will only be changed for the partcmd_update and
	 * partcmd_invalidate commands.
	 */
	adding = deleting = false;
	old_prs = new_prs = cs->partition_root_state;

	if (cmd == partcmd_invalidate) {
		if (is_partition_invalid(cs))
			return 0;

		/*
		 * Make the current partition invalid.
		 */
		if (is_partition_valid(parent))
			adding = cpumask_and(tmp->addmask,
					     cs->effective_xcpus,
					     parent->effective_xcpus);
		if (old_prs > 0)
			new_prs = -old_prs;

		goto write_error;
	}

	/*
	 * The parent must be a partition root.
	 * The new cpumask, if present, or the current cpus_allowed must
	 * not be empty.
	 */
	if (!is_partition_valid(parent)) {
		return is_partition_invalid(parent)
		       ? PERR_INVPARENT : PERR_NOTPART;
	}
	if (!newmask && xcpus_empty(cs))
		return PERR_CPUSEMPTY;

	nocpu = tasks_nocpu_error(parent, cs, xcpus);

	if ((cmd == partcmd_enable) || (cmd == partcmd_enablei)) {
		/*
		 * Need to call compute_excpus() in case
		 * exclusive_cpus not set. Sibling conflict should only happen
		 * if exclusive_cpus isn't set.
		 */
		xcpus = tmp->delmask;
		if (compute_excpus(cs, xcpus))
			WARN_ON_ONCE(!cpumask_empty(cs->exclusive_cpus));
		new_prs = (cmd == partcmd_enable) ? PRS_ROOT : PRS_ISOLATED;

		/*
		 * Enabling partition root is not allowed if its
		 * effective_xcpus is empty.
		 */
		if (cpumask_empty(xcpus))
			return PERR_INVCPUS;

		if (prstate_housekeeping_conflict(new_prs, xcpus))
			return PERR_HKEEPING;

		if ((new_prs == PRS_ISOLATED) && (new_prs != parent_prs) &&
		    !isolated_cpus_can_update(xcpus, NULL))
			return PERR_HKEEPING;

		if (tasks_nocpu_error(parent, cs, xcpus))
			return PERR_NOCPUS;

		/*
		 * This function will only be called when all the preliminary
		 * checks have passed. At this point, the following condition
		 * should hold.
		 *
		 * (cs->effective_xcpus & cpu_active_mask) ⊆ parent->effective_cpus
		 *
		 * Warn if it is not the case.
		 */
		cpumask_and(tmp->new_cpus, xcpus, cpu_active_mask);
		WARN_ON_ONCE(!cpumask_subset(tmp->new_cpus, parent->effective_cpus));

		deleting = true;
	} else if (cmd == partcmd_disable) {
		/*
		 * May need to add cpus back to parent's effective_cpus
		 * (and maybe removed from subpartitions_cpus/isolated_cpus)
		 * for valid partition root. xcpus may contain CPUs that
		 * shouldn't be removed from the two global cpumasks.
		 */
		if (is_partition_valid(cs)) {
			cpumask_copy(tmp->addmask, cs->effective_xcpus);
			adding = true;
		}
		new_prs = PRS_MEMBER;
	} else if (newmask) {
		/*
		 * Empty cpumask is not allowed
		 */
		if (cpumask_empty(newmask)) {
			part_error = PERR_CPUSEMPTY;
			goto write_error;
		}

		/* Check newmask again, whether cpus are available for parent/cs */
		nocpu |= tasks_nocpu_error(parent, cs, newmask);

		/*
		 * partcmd_update with newmask:
		 *
		 * Compute add/delete mask to/from effective_cpus
		 *
		 * For valid partition:
		 *   addmask = effective_xcpus & ~newmask
		 *			      & parent->effective_xcpus
		 *   delmask = newmask & ~effective_xcpus
		 *		       & parent->effective_xcpus
		 *
		 * For invalid partition:
		 *   delmask = newmask & parent->effective_xcpus
		 *   The partition may become valid soon.
		 */
		if (is_partition_invalid(cs)) {
			adding = false;
			deleting = cpumask_and(tmp->delmask,
					newmask, parent->effective_xcpus);
		} else {
			cpumask_andnot(tmp->addmask, cs->effective_xcpus, newmask);
			adding = cpumask_and(tmp->addmask, tmp->addmask,
					     parent->effective_xcpus);

			cpumask_andnot(tmp->delmask, newmask, cs->effective_xcpus);
			deleting = cpumask_and(tmp->delmask, tmp->delmask,
					       parent->effective_xcpus);
		}

		/*
		 * TBD: Invalidate a currently valid child root partition may
		 * still break isolated_cpus_can_update() rule if parent is an
		 * isolated partition.
		 */
		if (is_partition_valid(cs) && (old_prs != parent_prs)) {
			if ((parent_prs == PRS_ROOT) &&
			    /* Adding to parent means removing isolated CPUs */
			    !isolated_cpus_can_update(tmp->delmask, tmp->addmask))
				part_error = PERR_HKEEPING;
			if ((parent_prs == PRS_ISOLATED) &&
			    /* Adding to parent means adding isolated CPUs */
			    !isolated_cpus_can_update(tmp->addmask, tmp->delmask))
				part_error = PERR_HKEEPING;
		}

		/*
		 * The new CPUs to be removed from parent's effective CPUs
		 * must be present.
		 */
		if (deleting) {
			cpumask_and(tmp->new_cpus, tmp->delmask, cpu_active_mask);
			WARN_ON_ONCE(!cpumask_subset(tmp->new_cpus, parent->effective_cpus));
		}

		/*
		 * Make partition invalid if parent's effective_cpus could
		 * become empty and there are tasks in the parent.
		 */
		if (nocpu && (!adding ||
		    !cpumask_intersects(tmp->addmask, cpu_active_mask))) {
			part_error = PERR_NOCPUS;
			deleting = false;
			adding = cpumask_and(tmp->addmask,
					     cs->effective_xcpus, parent->effective_xcpus);
		}
	} else {
		/*
		 * partcmd_update w/o newmask
		 *
		 * delmask = effective_xcpus & parent->effective_cpus
		 *
		 * This can be called from:
		 * 1) update_cpumasks_hier()
		 * 2) cpuset_hotplug_update_tasks()
		 *
		 * Check to see if it can be transitioned from valid to
		 * invalid partition or vice versa.
		 *
		 * A partition error happens when parent has tasks and all
		 * its effective CPUs will have to be distributed out.
		 */
		if (nocpu) {
			part_error = PERR_NOCPUS;
			if (is_partition_valid(cs))
				adding = cpumask_and(tmp->addmask,
						     cs->effective_xcpus,
						     parent->effective_xcpus);
		} else if (is_partition_invalid(cs) && !cpumask_empty(xcpus) &&
			   cpumask_subset(xcpus, parent->effective_xcpus)) {
			struct cgroup_subsys_state *css;
			struct cpuset *child;
			bool exclusive = true;

			/*
			 * Convert invalid partition to valid has to
			 * pass the cpu exclusivity test.
			 */
			rcu_read_lock();
			cpuset_for_each_child(child, css, parent) {
				if (child == cs)
					continue;
				if (!cpusets_are_exclusive(cs, child)) {
					exclusive = false;
					break;
				}
			}
			rcu_read_unlock();
			if (exclusive)
				deleting = cpumask_and(tmp->delmask,
						xcpus, parent->effective_cpus);
			else
				part_error = PERR_NOTEXCL;
		}
	}

write_error:
	if (part_error)
		WRITE_ONCE(cs->prs_err, part_error);

	if (cmd == partcmd_update) {
		/*
		 * Check for possible transition between valid and invalid
		 * partition root.
		 */
		switch (cs->partition_root_state) {
		case PRS_ROOT:
		case PRS_ISOLATED:
			if (part_error)
				new_prs = -old_prs;
			break;
		case PRS_INVALID_ROOT:
		case PRS_INVALID_ISOLATED:
			if (!part_error)
				new_prs = -old_prs;
			break;
		}
	}

	if (!adding && !deleting && (new_prs == old_prs))
		return 0;

	/*
	 * Transitioning between invalid to valid or vice versa may require
	 * changing CS_CPU_EXCLUSIVE. In the case of partcmd_update,
	 * validate_change() has already been successfully called and
	 * CPU lists in cs haven't been updated yet. So defer it to later.
	 */
	if ((old_prs != new_prs) && (cmd != partcmd_update))  {
		int err = update_partition_exclusive_flag(cs, new_prs);

		if (err)
			return err;
	}

	/*
	 * Change the parent's effective_cpus & effective_xcpus (top cpuset
	 * only).
	 *
	 * Newly added CPUs will be removed from effective_cpus and
	 * newly deleted ones will be added back to effective_cpus.
	 */
	spin_lock_irq(&callback_lock);
	if (old_prs != new_prs)
		cs->partition_root_state = new_prs;

	/*
	 * Adding to parent's effective_cpus means deletion CPUs from cs
	 * and vice versa.
	 */
	if (adding)
		partition_xcpus_del(old_prs, parent, tmp->addmask);
	if (deleting)
		partition_xcpus_add(new_prs, parent, tmp->delmask);

	spin_unlock_irq(&callback_lock);

	if ((old_prs != new_prs) && (cmd == partcmd_update))
		update_partition_exclusive_flag(cs, new_prs);

	if (adding || deleting) {
		cpuset_update_tasks_cpumask(parent, tmp->addmask);
		update_sibling_cpumasks(parent, cs, tmp);
	}

	/*
	 * For partcmd_update without newmask, it is being called from
	 * cpuset_handle_hotplug(). Update the load balance flag and
	 * scheduling domain accordingly.
	 */
	if ((cmd == partcmd_update) && !newmask)
		update_partition_sd_lb(cs, old_prs);

	notify_partition_change(cs, old_prs);
	return 0;
}

/**
 * compute_partition_effective_cpumask - compute effective_cpus for partition
 * @cs: partition root cpuset
 * @new_ecpus: previously computed effective_cpus to be updated
 *
 * Compute the effective_cpus of a partition root by scanning effective_xcpus
 * of child partition roots and excluding their effective_xcpus.
 *
 * This has the side effect of invalidating valid child partition roots,
 * if necessary. Since it is called from either cpuset_hotplug_update_tasks()
 * or update_cpumasks_hier() where parent and children are modified
 * successively, we don't need to call update_parent_effective_cpumask()
 * and the child's effective_cpus will be updated in later iterations.
 *
 * Note that rcu_read_lock() is assumed to be held.
 */
static void compute_partition_effective_cpumask(struct cpuset *cs,
						struct cpumask *new_ecpus)
{
	struct cgroup_subsys_state *css;
	struct cpuset *child;
	bool populated = partition_is_populated(cs, NULL);

	/*
	 * Check child partition roots to see if they should be
	 * invalidated when
	 *  1) child effective_xcpus not a subset of new
	 *     excluisve_cpus
	 *  2) All the effective_cpus will be used up and cp
	 *     has tasks
	 */
	compute_excpus(cs, new_ecpus);
	cpumask_and(new_ecpus, new_ecpus, cpu_active_mask);

	rcu_read_lock();
	cpuset_for_each_child(child, css, cs) {
		if (!is_partition_valid(child))
			continue;

		/*
		 * There shouldn't be a remote partition underneath another
		 * partition root.
		 */
		WARN_ON_ONCE(is_remote_partition(child));
		WRITE_ONCE(child->prs_err, 0);
		if (!cpumask_subset(child->effective_xcpus,
				    cs->effective_xcpus))
			WRITE_ONCE(child->prs_err, PERR_INVCPUS);
		else if (populated &&
			 cpumask_subset(new_ecpus, child->effective_xcpus))
			WRITE_ONCE(child->prs_err, PERR_NOCPUS);

		if (child->prs_err) {
			int old_prs = child->partition_root_state;

			/*
			 * Invalidate child partition
			 */
			spin_lock_irq(&callback_lock);
			make_partition_invalid(child);
			spin_unlock_irq(&callback_lock);
			notify_partition_change(child, old_prs);
			continue;
		}
		cpumask_andnot(new_ecpus, new_ecpus,
			       child->effective_xcpus);
	}
	rcu_read_unlock();
}

/*
 * update_cpumasks_hier - Update effective cpumasks and tasks in the subtree
 * @cs:  the cpuset to consider
 * @tmp: temp variables for calculating effective_cpus & partition setup
 * @force: don't skip any descendant cpusets if set
 *
 * When configured cpumask is changed, the effective cpumasks of this cpuset
 * and all its descendants need to be updated.
 *
 * On legacy hierarchy, effective_cpus will be the same with cpu_allowed.
 *
 * Called with cpuset_mutex held
 */
static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
				 bool force)
{
	struct cpuset *cp;
	struct cgroup_subsys_state *pos_css;
	int old_prs, new_prs;

	rcu_read_lock();
	cpuset_for_each_descendant_pre(cp, pos_css, cs) {
		struct cpuset *parent = parent_cs(cp);
		bool remote = is_remote_partition(cp);
		bool update_parent = false;

		old_prs = new_prs = cp->partition_root_state;

		/*
		 * For child remote partition root (!= cs), we need to call
		 * remote_cpus_update() if effective_xcpus will be changed.
		 * Otherwise, we can skip the whole subtree.
		 *
		 * remote_cpus_update() will reuse tmp->new_cpus only after
		 * its value is being processed.
		 */
		if (remote && (cp != cs)) {
			compute_excpus(cp, tmp->new_cpus);
			if (cpumask_equal(cp->effective_xcpus, tmp->new_cpus)) {
				pos_css = css_rightmost_descendant(pos_css);
				continue;
			}
			rcu_read_unlock();
			remote_cpus_update(cp, NULL, tmp->new_cpus, tmp);
			rcu_read_lock();

			/* Remote partition may be invalidated */
			new_prs = cp->partition_root_state;
			remote = (new_prs == old_prs);
		}

		if (remote || (is_partition_valid(parent) && is_partition_valid(cp)))
			compute_partition_effective_cpumask(cp, tmp->new_cpus);
		else
			compute_effective_cpumask(tmp->new_cpus, cp, parent);

		if (remote)
			goto get_css;	/* Ready to update cpuset data */

		/*
		 * A partition with no effective_cpus is allowed as long as
		 * there is no task associated with it. Call
		 * update_parent_effective_cpumask() to check it.
		 */
		if (is_partition_valid(cp) && cpumask_empty(tmp->new_cpus)) {
			update_parent = true;
			goto update_parent_effective;
		}

		/*
		 * Skip the whole subtree if
		 * 1) the cpumask remains the same,
		 * 2) has no partition root state,
		 * 3) force flag not set, and
		 * 4) for v2 load balance state same as its parent.
		 */
		if (!cp->partition_root_state && !force &&
		    cpumask_equal(tmp->new_cpus, cp->effective_cpus) &&
		    (!cpuset_v2() ||
		    (is_sched_load_balance(parent) == is_sched_load_balance(cp)))) {
			pos_css = css_rightmost_descendant(pos_css);
			continue;
		}

update_parent_effective:
		/*
		 * update_parent_effective_cpumask() should have been called
		 * for cs already in update_cpumask(). We should also call
		 * cpuset_update_tasks_cpumask() again for tasks in the parent
		 * cpuset if the parent's effective_cpus changes.
		 */
		if ((cp != cs) && old_prs) {
			switch (parent->partition_root_state) {
			case PRS_ROOT:
			case PRS_ISOLATED:
				update_parent = true;
				break;

			default:
				/*
				 * When parent is not a partition root or is
				 * invalid, child partition roots become
				 * invalid too.
				 */
				if (is_partition_valid(cp))
					new_prs = -cp->partition_root_state;
				WRITE_ONCE(cp->prs_err,
					   is_partition_invalid(parent)
					   ? PERR_INVPARENT : PERR_NOTPART);
				break;
			}
		}
get_css:
		if (!css_tryget_online(&cp->css))
			continue;
		rcu_read_unlock();

		if (update_parent) {
			update_parent_effective_cpumask(cp, partcmd_update, NULL, tmp);
			/*
			 * The cpuset partition_root_state may become
			 * invalid. Capture it.
			 */
			new_prs = cp->partition_root_state;
		}

		spin_lock_irq(&callback_lock);
		cpumask_copy(cp->effective_cpus, tmp->new_cpus);
		cp->partition_root_state = new_prs;
		/*
		 * Need to compute effective_xcpus if either exclusive_cpus
		 * is non-empty or it is a valid partition root.
		 */
		if ((new_prs > 0) || !cpumask_empty(cp->exclusive_cpus))
			compute_excpus(cp, cp->effective_xcpus);
		if (new_prs <= 0)
			reset_partition_data(cp);
		spin_unlock_irq(&callback_lock);

		notify_partition_change(cp, old_prs);

		WARN_ON(!is_in_v2_mode() &&
			!cpumask_equal(cp->cpus_allowed, cp->effective_cpus));

		cpuset_update_tasks_cpumask(cp, tmp->new_cpus);

		/*
		 * On default hierarchy, inherit the CS_SCHED_LOAD_BALANCE
		 * from parent if current cpuset isn't a valid partition root
		 * and their load balance states differ.
		 */
		if (cpuset_v2() && !is_partition_valid(cp) &&
		    (is_sched_load_balance(parent) != is_sched_load_balance(cp))) {
			if (is_sched_load_balance(parent))
				set_bit(CS_SCHED_LOAD_BALANCE, &cp->flags);
			else
				clear_bit(CS_SCHED_LOAD_BALANCE, &cp->flags);
		}

		/*
		 * On legacy hierarchy, if the effective cpumask of any non-
		 * empty cpuset is changed, we need to rebuild sched domains.
		 * On default hierarchy, the cpuset needs to be a partition
		 * root as well.
		 */
		if (!cpumask_empty(cp->cpus_allowed) &&
		    is_sched_load_balance(cp) &&
		   (!cpuset_v2() || is_partition_valid(cp)))
			cpuset_force_rebuild();

		rcu_read_lock();
		css_put(&cp->css);
	}
	rcu_read_unlock();
}

/**
 * update_sibling_cpumasks - Update siblings cpumasks
 * @parent:  Parent cpuset
 * @cs:      Current cpuset
 * @tmp:     Temp variables
 */
static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
				    struct tmpmasks *tmp)
{
	struct cpuset *sibling;
	struct cgroup_subsys_state *pos_css;

	lockdep_assert_cpuset_lock_held();

	/*
	 * Check all its siblings and call update_cpumasks_hier()
	 * if their effective_cpus will need to be changed.
	 *
	 * It is possible a change in parent's effective_cpus
	 * due to a change in a child partition's effective_xcpus will impact
	 * its siblings even if they do not inherit parent's effective_cpus
	 * directly. It should not impact valid partition.
	 *
	 * The update_cpumasks_hier() function may sleep. So we have to
	 * release the RCU read lock before calling it.
	 */
	rcu_read_lock();
	cpuset_for_each_child(sibling, pos_css, parent) {
		if (sibling == cs || is_partition_valid(sibling))
			continue;

		compute_effective_cpumask(tmp->new_cpus, sibling,
					  parent);
		if (cpumask_equal(tmp->new_cpus, sibling->effective_cpus))
			continue;

		if (!css_tryget_online(&sibling->css))
			continue;

		rcu_read_unlock();
		update_cpumasks_hier(sibling, tmp, false);
		rcu_read_lock();
		css_put(&sibling->css);
	}
	rcu_read_unlock();
}

static int parse_cpuset_cpulist(const char *buf, struct cpumask *out_mask)
{
	int retval;

	retval = cpulist_parse(buf, out_mask);
	if (retval < 0)
		return retval;
	if (!cpumask_subset(out_mask, top_cpuset.cpus_allowed))
		return -EINVAL;

	return 0;
}

/**
 * validate_partition - Validate a cpuset partition configuration
 * @cs: The cpuset to validate
 * @trialcs: The trial cpuset containing proposed configuration changes
 *
 * If any validation check fails, the appropriate error code is set in the
 * cpuset's prs_err field.
 *
 * Return: PRS error code (0 if valid, non-zero error code if invalid)
 */
static enum prs_errcode validate_partition(struct cpuset *cs, struct cpuset *trialcs)
{
	struct cpuset *parent = parent_cs(cs);

	if (cs_is_member(trialcs))
		return PERR_NONE;

	if (cpumask_empty(trialcs->effective_xcpus))
		return PERR_INVCPUS;

	if (prstate_housekeeping_conflict(trialcs->partition_root_state,
					  trialcs->effective_xcpus))
		return PERR_HKEEPING;

	if (tasks_nocpu_error(parent, cs, trialcs->effective_xcpus))
		return PERR_NOCPUS;

	return PERR_NONE;
}

/**
 * partition_cpus_change - Handle partition state changes due to CPU mask updates
 * @cs: The target cpuset being modified
 * @trialcs: The trial cpuset containing proposed configuration changes
 * @tmp: Temporary masks for intermediate calculations
 *
 * This function handles partition state transitions triggered by CPU mask changes.
 * CPU modifications may cause a partition to be disabled or require state updates.
 */
static void partition_cpus_change(struct cpuset *cs, struct cpuset *trialcs,
					struct tmpmasks *tmp)
{
	enum prs_errcode prs_err;

	if (cs_is_member(cs))
		return;

	prs_err = validate_partition(cs, trialcs);
	if (prs_err) {
		WRITE_ONCE(cs->prs_err, prs_err);
		trialcs->prs_err = prs_err;
	}

	if (is_remote_partition(cs)) {
		if (trialcs->prs_err)
			remote_partition_disable(cs, tmp);
		else
			remote_cpus_update(cs, trialcs->exclusive_cpus,
					   trialcs->effective_xcpus, tmp);
	} else {
		if (trialcs->prs_err)
			update_parent_effective_cpumask(cs, partcmd_invalidate,
							NULL, tmp);
		else
			update_parent_effective_cpumask(cs, partcmd_update,
							trialcs->effective_xcpus, tmp);
	}
}

/**
 * update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
 * @cs: the cpuset to consider
 * @trialcs: trial cpuset
 * @buf: buffer of cpu numbers written to this cpuset
 */
static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
			  const char *buf)
{
	int retval;
	struct tmpmasks tmp;
	bool force = false;
	int old_prs = cs->partition_root_state;

	retval = parse_cpuset_cpulist(buf, trialcs->cpus_allowed);
	if (retval < 0)
		return retval;

	/* Nothing to do if the cpus didn't change */
	if (cpumask_equal(cs->cpus_allowed, trialcs->cpus_allowed))
		return 0;

	compute_trialcs_excpus(trialcs, cs);
	trialcs->prs_err = PERR_NONE;

	retval = validate_change(cs, trialcs);
	if (retval < 0)
		return retval;

	if (alloc_tmpmasks(&tmp))
		return -ENOMEM;

	/*
	 * Check all the descendants in update_cpumasks_hier() if
	 * effective_xcpus is to be changed.
	 */
	force = !cpumask_equal(cs->effective_xcpus, trialcs->effective_xcpus);

	partition_cpus_change(cs, trialcs, &tmp);

	spin_lock_irq(&callback_lock);
	cpumask_copy(cs->cpus_allowed, trialcs->cpus_allowed);
	cpumask_copy(cs->effective_xcpus, trialcs->effective_xcpus);
	if ((old_prs > 0) && !is_partition_valid(cs))
		reset_partition_data(cs);
	spin_unlock_irq(&callback_lock);

	/* effective_cpus/effective_xcpus will be updated here */
	update_cpumasks_hier(cs, &tmp, force);

	/* Update CS_SCHED_LOAD_BALANCE and/or sched_domains, if necessary */
	if (cs->partition_root_state)
		update_partition_sd_lb(cs, old_prs);

	free_tmpmasks(&tmp);
	return retval;
}

/**
 * update_exclusive_cpumask - update the exclusive_cpus mask of a cpuset
 * @cs: the cpuset to consider
 * @trialcs: trial cpuset
 * @buf: buffer of cpu numbers written to this cpuset
 *
 * The tasks' cpumask will be updated if cs is a valid partition root.
 */
static int update_exclusive_cpumask(struct cpuset *cs, struct cpuset *trialcs,
				    const char *buf)
{
	int retval;
	struct tmpmasks tmp;
	bool force = false;
	int old_prs = cs->partition_root_state;

	retval = parse_cpuset_cpulist(buf, trialcs->exclusive_cpus);
	if (retval < 0)
		return retval;

	/* Nothing to do if the CPUs didn't change */
	if (cpumask_equal(cs->exclusive_cpus, trialcs->exclusive_cpus))
		return 0;

	/*
	 * Reject the change if there is exclusive CPUs conflict with
	 * the siblings.
	 */
	if (compute_trialcs_excpus(trialcs, cs))
		return -EINVAL;

	/*
	 * Check all the descendants in update_cpumasks_hier() if
	 * effective_xcpus is to be changed.
	 */
	force = !cpumask_equal(cs->effective_xcpus, trialcs->effective_xcpus);

	retval = validate_change(cs, trialcs);
	if (retval)
		return retval;

	if (alloc_tmpmasks(&tmp))
		return -ENOMEM;

	trialcs->prs_err = PERR_NONE;
	partition_cpus_change(cs, trialcs, &tmp);

	spin_lock_irq(&callback_lock);
	cpumask_copy(cs->exclusive_cpus, trialcs->exclusive_cpus);
	cpumask_copy(cs->effective_xcpus, trialcs->effective_xcpus);
	if ((old_prs > 0) && !is_partition_valid(cs))
		reset_partition_data(cs);
	spin_unlock_irq(&callback_lock);

	/*
	 * Call update_cpumasks_hier() to update effective_cpus/effective_xcpus
	 * of the subtree when it is a valid partition root or effective_xcpus
	 * is updated.
	 */
	if (is_partition_valid(cs) || force)
		update_cpumasks_hier(cs, &tmp, force);

	/* Update CS_SCHED_LOAD_BALANCE and/or sched_domains, if necessary */
	if (cs->partition_root_state)
		update_partition_sd_lb(cs, old_prs);

	free_tmpmasks(&tmp);
	return 0;
}

/*
 * Migrate memory region from one set of nodes to another.  This is
 * performed asynchronously as it can be called from process migration path
 * holding locks involved in process management.  All mm migrations are
 * performed in the queued order and can be waited for by flushing
 * cpuset_migrate_mm_wq.
 */

struct cpuset_migrate_mm_work {
	struct work_struct	work;
	struct mm_struct	*mm;
	nodemask_t		from;
	nodemask_t		to;
};

static void cpuset_migrate_mm_workfn(struct work_struct *work)
{
	struct cpuset_migrate_mm_work *mwork =
		container_of(work, struct cpuset_migrate_mm_work, work);

	/* on a wq worker, no need to worry about %current's mems_allowed */
	do_migrate_pages(mwork->mm, &mwork->from, &mwork->to, MPOL_MF_MOVE_ALL);
	mmput(mwork->mm);
	kfree(mwork);
}

static void cpuset_migrate_mm(struct mm_struct *mm, const nodemask_t *from,
							const nodemask_t *to)
{
	struct cpuset_migrate_mm_work *mwork;

	if (nodes_equal(*from, *to)) {
		mmput(mm);
		return;
	}

	mwork = kzalloc_obj(*mwork);
	if (mwork) {
		mwork->mm = mm;
		mwork->from = *from;
		mwork->to = *to;
		INIT_WORK(&mwork->work, cpuset_migrate_mm_workfn);
		queue_work(cpuset_migrate_mm_wq, &mwork->work);
	} else {
		mmput(mm);
	}
}

static void flush_migrate_mm_task_workfn(struct callback_head *head)
{
	flush_workqueue(cpuset_migrate_mm_wq);
	kfree(head);
}

static void schedule_flush_migrate_mm(void)
{
	struct callback_head *flush_cb;

	flush_cb = kzalloc_obj(struct callback_head);
	if (!flush_cb)
		return;

	init_task_work(flush_cb, flush_migrate_mm_task_workfn);

	if (task_work_add(current, flush_cb, TWA_RESUME))
		kfree(flush_cb);
}

/*
 * cpuset_change_task_nodemask - change task's mems_allowed and mempolicy
 * @tsk: the task to change
 * @newmems: new nodes that the task will be set
 *
 * We use the mems_allowed_seq seqlock to safely update both tsk->mems_allowed
 * and rebind an eventual tasks' mempolicy. If the task is allocating in
 * parallel, it might temporarily see an empty intersection, which results in
 * a seqlock check and retry before OOM or allocation failure.
 */
static void cpuset_change_task_nodemask(struct task_struct *tsk,
					nodemask_t *newmems)
{
	task_lock(tsk);

	local_irq_disable();
	write_seqcount_begin(&tsk->mems_allowed_seq);

	nodes_or(tsk->mems_allowed, tsk->mems_allowed, *newmems);
	mpol_rebind_task(tsk, newmems);
	tsk->mems_allowed = *newmems;

	write_seqcount_end(&tsk->mems_allowed_seq);
	local_irq_enable();

	task_unlock(tsk);
}

static void *cpuset_being_rebound;

/**
 * cpuset_update_tasks_nodemask - Update the nodemasks of tasks in the cpuset.
 * @cs: the cpuset in which each task's mems_allowed mask needs to be changed
 *
 * Iterate through each task of @cs updating its mems_allowed to the
 * effective cpuset's.  As this function is called with cpuset_mutex held,
 * cpuset membership stays stable.
 *
 * - cpuset_change_task_nodemask(): guarantee_online_mems()
 * - mpol_rebind_mm(): effective_mems
 * - cpuset_migrate_mm(): guarantee_online_mems()
 * - old_mems_allowed: guarantee_online_mems()
 *
 * For v2, guarantee_online_mems() should return a node mask that is the same
 * as the effective_mems of current cpuset.
 */
void cpuset_update_tasks_nodemask(struct cpuset *cs)
{
	static nodemask_t newmems;	/* protected by cpuset_mutex */
	struct css_task_iter it;
	struct task_struct *task;

	cpuset_being_rebound = cs;		/* causes mpol_dup() rebind */
	guarantee_online_mems(cs, &newmems);

	/*
	 * The mpol_rebind_mm() call takes mmap_lock, which we couldn't
	 * take while holding tasklist_lock.  Forks can happen - the
	 * mpol_dup() cpuset_being_rebound check will catch such forks,
	 * and rebind their vma mempolicies too.  Because we still hold
	 * the global cpuset_mutex, we know that no other rebind effort
	 * will be contending for the global variable cpuset_being_rebound.
	 * It's ok if we rebind the same mm twice; mpol_rebind_mm()
	 * is idempotent.  Also migrate pages in each mm to new nodes.
	 */
	css_task_iter_start(&cs->css, 0, &it);
	while ((task = css_task_iter_next(&it))) {
		struct mm_struct *mm;
		bool migrate;

		cpuset_change_task_nodemask(task, &newmems);

		/* Rebind and migrate mm only for thread group leader */
		if (!thread_group_leader(task))
			continue;

		mm = get_task_mm(task);
		if (!mm)
			continue;

		migrate = is_memory_migrate(cs);

		/*
		 * For v1 we can have empty effective_mems, but we cannot
		 * attach any tasks (see cpuset_can_attach_check()). For v2,
		 * effective_mems is guaranteed to not be empty.
		 */
		mpol_rebind_mm(mm, &cs->effective_mems);
		if (migrate)
			cpuset_migrate_mm(mm, &cs->old_mems_allowed, &newmems);
		else
			mmput(mm);
	}
	css_task_iter_end(&it);

	/*
	 * All the tasks' nodemasks have been updated, update
	 * cs->old_mems_allowed.
	 */
	cs->old_mems_allowed = newmems;

	/* We're done rebinding vmas to this cpuset's new mems_allowed. */
	cpuset_being_rebound = NULL;
}

/*
 * update_nodemasks_hier - Update effective nodemasks and tasks in the subtree
 * @cs: the cpuset to consider
 * @new_mems: a temp variable for calculating new effective_mems
 *
 * When configured nodemask is changed, the effective nodemasks of this cpuset
 * and all its descendants need to be updated.
 *
 * On legacy hierarchy, effective_mems will be the same with mems_allowed.
 *
 * Called with cpuset_mutex held
 */
static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
{
	struct cpuset *cp;
	struct cgroup_subsys_state *pos_css;

	rcu_read_lock();
	cpuset_for_each_descendant_pre(cp, pos_css, cs) {
		struct cpuset *parent = parent_cs(cp);

		compute_effective_nodemask(new_mems, cp, parent);

		/* Skip the whole subtree if the nodemask remains the same. */
		if (nodes_equal(*new_mems, cp->effective_mems)) {
			pos_css = css_rightmost_descendant(pos_css);
			continue;
		}

		if (!css_tryget_online(&cp->css))
			continue;
		rcu_read_unlock();

		spin_lock_irq(&callback_lock);
		cp->effective_mems = *new_mems;
		spin_unlock_irq(&callback_lock);

		WARN_ON(!is_in_v2_mode() &&
			!nodes_equal(cp->mems_allowed, cp->effective_mems));

		cpuset_update_tasks_nodemask(cp);

		rcu_read_lock();
		css_put(&cp->css);
	}
	rcu_read_unlock();
}

/*
 * Handle user request to change the 'mems' memory placement
 * of a cpuset.  Needs to validate the request, update the
 * cpusets mems_allowed, and for each task in the cpuset,
 * update mems_allowed and rebind task's mempolicy and any vma
 * mempolicies and if the cpuset is marked 'memory_migrate',
 * migrate the tasks pages to the new memory.
 *
 * Call with cpuset_mutex held. May take callback_lock during call.
 * Will take tasklist_lock, scan tasklist for tasks in cpuset cs,
 * lock each such tasks mm->mmap_lock, scan its vma's and rebind
 * their mempolicies to the cpusets new mems_allowed.
 */
static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
			   const char *buf)
{
	int retval;

	/*
	 * An empty mems_allowed is ok iff there are no tasks in the cpuset.
	 * The validate_change() call ensures that cpusets with tasks have memory.
	 */
	retval = nodelist_parse(buf, trialcs->mems_allowed);
	if (retval < 0)
		return retval;

	if (!nodes_subset(trialcs->mems_allowed,
			  top_cpuset.mems_allowed))
		return -EINVAL;

	/* No change? nothing to do */
	if (nodes_equal(cs->mems_allowed, trialcs->mems_allowed))
		return 0;

	retval = validate_change(cs, trialcs);
	if (retval < 0)
		return retval;

	check_insane_mems_config(&trialcs->mems_allowed);

	spin_lock_irq(&callback_lock);
	cs->mems_allowed = trialcs->mems_allowed;
	spin_unlock_irq(&callback_lock);

	/* use trialcs->mems_allowed as a temp variable */
	update_nodemasks_hier(cs, &trialcs->mems_allowed);
	return 0;
}

bool current_cpuset_is_being_rebound(void)
{
	bool ret;

	rcu_read_lock();
	ret = task_cs(current) == cpuset_being_rebound;
	rcu_read_unlock();

	return ret;
}

/*
 * cpuset_update_flag - read a 0 or a 1 in a file and update associated flag
 * bit:		the bit to update (see cpuset_flagbits_t)
 * cs:		the cpuset to update
 * turning_on: 	whether the flag is being set or cleared
 *
 * Call with cpuset_mutex held.
 */

int cpuset_update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
		       int turning_on)
{
	struct cpuset *trialcs;
	int balance_flag_changed;
	int spread_page_changed;
	int err;

	trialcs = dup_or_alloc_cpuset(cs);
	if (!trialcs)
		return -ENOMEM;

	if (turning_on)
		set_bit(bit, &trialcs->flags);
	else
		clear_bit(bit, &trialcs->flags);

	err = validate_change(cs, trialcs);
	if (err < 0)
		goto out;

	balance_flag_changed = (is_sched_load_balance(cs) !=
				is_sched_load_balance(trialcs));

	spread_page_changed = is_spread_page(cs) != is_spread_page(trialcs);

	spin_lock_irq(&callback_lock);
	cs->flags = trialcs->flags;
	spin_unlock_irq(&callback_lock);

	if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed) {
		if (cpuset_v2())
			cpuset_force_rebuild();
		else
			rebuild_sched_domains_locked();
	}

	if (spread_page_changed)
		cpuset1_update_tasks_flags(cs);
out:
	free_cpuset(trialcs);
	return err;
}

/**
 * update_prstate - update partition_root_state
 * @cs: the cpuset to update
 * @new_prs: new partition root state
 * Return: 0 if successful, != 0 if error
 *
 * Call with cpuset_mutex held.
 */
static int update_prstate(struct cpuset *cs, int new_prs)
{
	int err = PERR_NONE, old_prs = cs->partition_root_state;
	struct cpuset *parent = parent_cs(cs);
	struct tmpmasks tmpmask;
	bool isolcpus_updated = false;

	if (old_prs == new_prs)
		return 0;

	/*
	 * Treat a previously invalid partition root as if it is a "member".
	 */
	if (new_prs && is_partition_invalid(cs))
		old_prs = PRS_MEMBER;

	if (alloc_tmpmasks(&tmpmask))
		return -ENOMEM;

	err = update_partition_exclusive_flag(cs, new_prs);
	if (err)
		goto out;

	if (!old_prs) {
		/*
		 * cpus_allowed and exclusive_cpus cannot be both empty.
		 */
		if (xcpus_empty(cs)) {
			err = PERR_CPUSEMPTY;
			goto out;
		}

		/*
		 * We don't support the creation of a new local partition with
		 * a remote partition underneath it. This unsupported
		 * setting can happen only if parent is the top_cpuset because
		 * a remote partition cannot be created underneath an existing
		 * local or remote partition.
		 */
		if ((parent == &top_cpuset) &&
		    cpumask_intersects(cs->exclusive_cpus, subpartitions_cpus)) {
			err = PERR_REMOTE;
			goto out;
		}

		/*
		 * If parent is valid partition, enable local partiion.
		 * Otherwise, enable a remote partition.
		 */
		if (is_partition_valid(parent)) {
			enum partition_cmd cmd = (new_prs == PRS_ROOT)
					       ? partcmd_enable : partcmd_enablei;

			err = update_parent_effective_cpumask(cs, cmd, NULL, &tmpmask);
		} else {
			err = remote_partition_enable(cs, new_prs, &tmpmask);
		}
	} else if (old_prs && new_prs) {
		/*
		 * A change in load balance state only, no change in cpumasks.
		 * Need to update isolated_cpus.
		 */
		if (((new_prs == PRS_ISOLATED) &&
		     !isolated_cpus_can_update(cs->effective_xcpus, NULL)) ||
		    prstate_housekeeping_conflict(new_prs, cs->effective_xcpus))
			err = PERR_HKEEPING;
		else
			isolcpus_updated = true;
	} else {
		/*
		 * Switching back to member is always allowed even if it
		 * disables child partitions.
		 */
		if (is_remote_partition(cs))
			remote_partition_disable(cs, &tmpmask);
		else
			update_parent_effective_cpumask(cs, partcmd_disable,
							NULL, &tmpmask);

		/*
		 * Invalidation of child partitions will be done in
		 * update_cpumasks_hier().
		 */
	}
out:
	/*
	 * Make partition invalid & disable CS_CPU_EXCLUSIVE if an error
	 * happens.
	 */
	if (err) {
		new_prs = -new_prs;
		update_partition_exclusive_flag(cs, new_prs);
	}

	spin_lock_irq(&callback_lock);
	cs->partition_root_state = new_prs;
	WRITE_ONCE(cs->prs_err, err);
	if (!is_partition_valid(cs))
		reset_partition_data(cs);
	else if (isolcpus_updated)
		isolated_cpus_update(old_prs, new_prs, cs->effective_xcpus);
	spin_unlock_irq(&callback_lock);

	/* Force update if switching back to member & update effective_xcpus */
	update_cpumasks_hier(cs, &tmpmask, !new_prs);

	/* A newly created partition must have effective_xcpus set */
	WARN_ON_ONCE(!old_prs && (new_prs > 0)
			      && cpumask_empty(cs->effective_xcpus));

	/* Update sched domains and load balance flag */
	update_partition_sd_lb(cs, old_prs);

	notify_partition_change(cs, old_prs);
	if (force_sd_rebuild)
		rebuild_sched_domains_locked();
	free_tmpmasks(&tmpmask);
	return 0;
}

/*
 * Check to see if a cpuset can accept a new task
 * For v1, cpus_allowed and mems_allowed can't be empty.
 * For v2, effective_cpus can't be empty.
 * Note that in v1, effective_cpus = cpus_allowed.
 *
 * Also set the boolean flag passed in by @psetsched depending on if
 * security_task_setscheduler() call is needed and @oldcs is not NULL.
 */
static int cpuset_can_attach_check(struct cpuset *cs, struct cpuset *oldcs,
				   bool *psetsched)
{
	bool cpus_updated, mems_updated;

	if (cpumask_empty(cs->effective_cpus) ||
	   (!is_in_v2_mode() && nodes_empty(cs->mems_allowed)))
		return -ENOSPC;

	if (!oldcs)
		return 0;

	if (!llist_on_list(&oldcs->attach_node))
		llist_add(&oldcs->attach_node, &src_cs_head);

	if (!llist_on_list(&cs->attach_node))
		llist_add(&cs->attach_node, &dst_cs_head);

	cpus_updated = !cpumask_equal(cs->effective_cpus, oldcs->effective_cpus);
	mems_updated = !nodes_equal(cs->effective_mems, oldcs->effective_mems);

	if (cpus_updated)
		attach_ctx.cpus_updated = true;
	if (mems_updated)
		attach_ctx.mems_updated = true;

	/*
	 * Skip rights over task setsched check in v2 when nothing changes for
	 * the current oldcs/cs pair, migration permission derives from
	 * hierarchy ownership in cgroup_procs_write_permission()).
	 */
	*psetsched = !cpuset_v2() || cpus_updated || mems_updated;

	/*
	 * A v1 cpuset with tasks will have no CPU left only when CPU hotplug
	 * brings the last online CPU offline as users are not allowed to empty
	 * cpuset.cpus when there are active tasks inside. When that happens,
	 * we should allow tasks to migrate out without security check to make
	 * sure they will be able to run after migration.
	 */
	if (!is_in_v2_mode() && cpumask_empty(oldcs->effective_cpus))
		*psetsched = false;

	return 0;
}

static int cpuset_reserve_dl_bw(void)
{
	struct cpuset *cs;
	int cpu, ret;

	llist_for_each_entry(cs, dst_cs_head.first, attach_node) {
		if (!cs->sum_migrate_dl_bw)
			continue;

		cpu = cpumask_any_and(cpu_active_mask, cs->effective_cpus);
		if (unlikely(cpu >= nr_cpu_ids))
			return -EINVAL;

		ret = dl_bw_alloc(cpu, cs->sum_migrate_dl_bw);
		if (ret)
			return ret;

		cs->dl_bw_cpu = cpu;
	}
	return 0;
}

/*
 * Clear and optionally apply (@cancel is false) the attach related data in the
 * source or destination cpuset.
 */
static void clear_attach_data(struct llist_head *head, bool cancel)
{
	struct cpuset *cs, *next;
	struct llist_node *lnode = __llist_del_all(head);

	llist_for_each_entry_safe(cs, next, lnode, attach_node) {
		init_llist_node(&cs->attach_node);
		if (cs->nr_migrate_dl_tasks) {
			if (!cancel)
				atomic_add(cs->nr_migrate_dl_tasks, &cs->nr_deadline_tasks);
			else if (cs->dl_bw_cpu >= 0) /* && cancel */
				dl_bw_free(cs->dl_bw_cpu, cs->sum_migrate_dl_bw);
			cs->nr_migrate_dl_tasks = 0;
			cs->sum_migrate_dl_bw = 0;
			cs->dl_bw_cpu = -1;
		}
	}
}

/* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
static int cpuset_can_attach(struct cgroup_taskset *tset)
{
	struct cgroup_subsys_state *css;
	struct cpuset *cs, *oldcs;
	struct task_struct *task;
	bool setsched_check;
	int ret;

	cs = oldcs = NULL;
	mutex_lock(&cpuset_mutex);
	attach_ctx.old_cs = NULL;	/* Used later in cpuset_attach_task() */
	attach_ctx.cpus_updated = false;
	attach_ctx.mems_updated = false;
	attach_ctx.many_dest_cs = false;

	/*
	 * The attach_ctx.old_cs is used mainly by cpuset_migrate_mm() to get
	 * the old_mems_allowed value. There are two ways that many-to-one
	 * cpuset migration can happen:
	 * 1) A multithread application with threads in different cpusets is
	 *    wholely migrated to a new cpuset.
	 * 2) Disabling v2 cpuset controller will move all the tasks in child
	 *    cpusets to the parent cpuset.
	 *
	 * In the former case, it is the mm setting of the group leader that
	 * really matters. So attach_ctx.old_cs should track the oldcs of the
	 * group leader. It falls back to the oldcs of the first task if there
	 * is no group leader in the taskset. In the latter case, effective_mems
	 * of child cpusets must always be a subset of the parent. So no real
	 * page migration will be necessary no matter which child cpuset is
	 * selected as attach_ctx.old_cs.
	 *
	 * For a v2 threaded subtree where cpuset isn't enabled in some of the
	 * cgroups, it is possible that oldcs == cs for some of the tasks.
	 * In this case, we can skip checking on those tasks as there is no
	 * actual migration wrt cpuset.
	 */
	cgroup_taskset_for_each(task, css, tset) {
		struct cpuset *new_cs = css_cs(css);
		struct cpuset *new_oldcs = task_cs(task);

		if ((new_oldcs != oldcs) || (new_cs != cs)) {
			if (cs && (new_cs != cs))
				attach_ctx.many_dest_cs = true;
			cs = new_cs;
			oldcs = new_oldcs;
			if (oldcs == cs)
				continue;
			if (!attach_ctx.old_cs)
				attach_ctx.old_cs = oldcs;
			ret = cpuset_can_attach_check(cs, oldcs, &setsched_check);
			if (ret)
				goto out_unlock;
		}

		if (oldcs == cs)
			continue;

		ret = task_can_attach(task);
		if (ret)
			goto out_unlock;

		/* Update attach_ctx.old_cs to the latest group leader */
		if (task == task->group_leader)
			attach_ctx.old_cs = task_cs(task);

		if (setsched_check) {
			ret = security_task_setscheduler(task);
			if (ret)
				goto out_unlock;
		}

		if (dl_task(task)) {
			/*
			 * Count all migrating DL tasks for cpuset task accounting.
			 * Only tasks that need a root-domain bandwidth move
			 * contribute to sum_migrate_dl_bw.
			 */
			cs->nr_migrate_dl_tasks++;
			oldcs->nr_migrate_dl_tasks--;
			if (dl_task_needs_bw_move(task, cs->effective_cpus))
				cs->sum_migrate_dl_bw += task->dl.dl_bw;
		}
	}

	/*
	 * The only case where there are multiple destination cpusets for
	 * task migration is when enabling a v2 cpuset controllers where
	 * tasks will be migrated to multiple child cpusets from a parent
	 * cpuset with the same effective CPUs and memory nodes. IOW,
	 * both attach_cpus_updated and attach_mems_updated should be false.
	 * If not, it is a condition that the current code cannot handle.
	 * Print a warning and abort the attach operation as further code
	 * change may be needed.
	 */
	if (WARN_ON_ONCE(attach_ctx.many_dest_cs && (!cpuset_v2() ||
			 attach_ctx.cpus_updated || attach_ctx.mems_updated))) {
		ret = -EINVAL;
		goto out_unlock;
	}

	ret = cpuset_reserve_dl_bw();

out_unlock:
	if (ret) {
		clear_attach_data(&src_cs_head, true);
		clear_attach_data(&dst_cs_head, true);
	} else {
		attach_ctx.in_progress++;
	}

	mutex_unlock(&cpuset_mutex);
	return ret;
}

static void cpuset_cancel_attach(struct cgroup_taskset *tset)
{
	mutex_lock(&cpuset_mutex);
	dec_attach_in_progress_locked();
	clear_attach_data(&src_cs_head, true);
	clear_attach_data(&dst_cs_head, true);
	mutex_unlock(&cpuset_mutex);
}

/*
 * Protected by cpuset_mutex. cpus_attach is used only by cpuset_attach_task()
 * but we can't allocate it dynamically there.  Define it global and
 * allocate from cpuset_init().
 */
static cpumask_var_t cpus_attach;

static void cpuset_attach_task(struct cpuset *cs, struct task_struct *task)
{
	struct mm_struct *mm;

	lockdep_assert_cpuset_lock_held();

	if (cs != &top_cpuset)
		guarantee_active_cpus(task, cpus_attach);
	else
		cpumask_andnot(cpus_attach, task_cpu_possible_mask(task),
			       subpartitions_cpus);
	/*
	 * can_attach beforehand should guarantee that this doesn't
	 * fail.  TODO: have a better way to handle failure here
	 */
	WARN_ON_ONCE(set_cpus_allowed_ptr(task, cpus_attach));

	if (cpuset_v2() && !attach_ctx.mems_updated)
		return;

	cpuset_change_task_nodemask(task, &attach_ctx.nodemask_to);
	cpuset1_update_task_spread_flags(cs, task);

	if ((task != task->group_leader) || !attach_ctx.mems_updated)
		return;

	/*
	 * Change mm for threadgroup leader. This is expensive and may
	 * sleep and should be moved outside migration path proper.
	 */
	mm = get_task_mm(task);
	if (mm) {
		struct cpuset *oldcs = attach_ctx.old_cs;

		mpol_rebind_mm(mm, &cs->effective_mems);

		/*
		 * old_mems_allowed is the same with mems_allowed
		 * here, except if this task is being moved
		 * automatically due to hotplug.  In that case
		 * @mems_allowed has been updated and is empty, so
		 * @old_mems_allowed is the right nodesets that we
		 * migrate mm from.
		 */
		if (is_memory_migrate(cs)) {
			cpuset_migrate_mm(mm, &oldcs->old_mems_allowed,
					  &attach_ctx.nodemask_to);
			attach_ctx.task_work_queued = true;
		} else {
			mmput(mm);
		}
	}
}

static void cpuset_attach(struct cgroup_taskset *tset)
{
	struct task_struct *task;
	struct cgroup_subsys_state *css;
	struct cpuset *cs;

	cgroup_taskset_first(tset, &css);
	cs = css_cs(css);

	lockdep_assert_cpus_held();	/* see cgroup_attach_lock() */
	mutex_lock(&cpuset_mutex);
	attach_ctx.task_work_queued = false;
	guarantee_online_mems(cs, &attach_ctx.nodemask_to);

	/*
	 * attach_ctx.old_cs can only be NULL if no task is actually migrating.
	 * This is highly unlikely. If it happens at all, we can skip task
	 * iteration and setting old_mems_allowed.
	 */
	if (unlikely(!attach_ctx.old_cs))
		goto out;

	/*
	 * In the default hierarchy, enabling cpuset in the child cgroups
	 * will trigger a cpuset_attach() call with no change in effective cpus
	 * and mems. In that case, we can optimize out by skipping the task
	 * iteration and the destination cpuset list is iterated to set
	 * old_mems_allowed.
	 */
	if (cpuset_v2() && !attach_ctx.cpus_updated && !attach_ctx.mems_updated) {
		llist_for_each_entry(cs, dst_cs_head.first, attach_node)
			cs->old_mems_allowed = attach_ctx.nodemask_to;
		goto out;
	}

	cgroup_taskset_for_each(task, css, tset)
		cpuset_attach_task(cs, task);

	if (attach_ctx.task_work_queued)
		schedule_flush_migrate_mm();
	cs->old_mems_allowed = attach_ctx.nodemask_to;
out:
	clear_attach_data(&src_cs_head, false);
	clear_attach_data(&dst_cs_head, false);
	dec_attach_in_progress_locked();

	mutex_unlock(&cpuset_mutex);
}

/*
 * Common handling for a write to a "cpus" or "mems" file.
 */
ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
				    char *buf, size_t nbytes, loff_t off)
{
	struct cpuset *cs = css_cs(of_css(of));
	struct cpuset *trialcs;
	int retval = -ENODEV;

	/* root is read-only */
	if (cs == &top_cpuset)
		return -EACCES;

	buf = strstrip(buf);

	/* cpuset_mutex acquired in wait_attach_done_lock() */
	mutex_lock(&cpuset_top_mutex);
	cpus_read_lock();
	wait_attach_done_lock();

	if (!is_cpuset_online(cs))
		goto out_unlock;

	trialcs = dup_or_alloc_cpuset(cs);
	if (!trialcs) {
		retval = -ENOMEM;
		goto out_unlock;
	}

	switch (of_cft(of)->private) {
	case FILE_CPULIST:
		retval = update_cpumask(cs, trialcs, buf);
		break;
	case FILE_EXCLUSIVE_CPULIST:
		retval = update_exclusive_cpumask(cs, trialcs, buf);
		break;
	case FILE_MEMLIST:
		retval = update_nodemask(cs, trialcs, buf);
		break;
	default:
		retval = -EINVAL;
		break;
	}

	free_cpuset(trialcs);
out_unlock:
	cpuset_update_sd_hk_unlock();
	if (of_cft(of)->private == FILE_MEMLIST)
		schedule_flush_migrate_mm();
	return retval ?: nbytes;
}

/*
 * These ascii lists should be read in a single call, by using a user
 * buffer large enough to hold the entire map.  If read in smaller
 * chunks, there is no guarantee of atomicity.  Since the display format
 * used, list of ranges of sequential numbers, is variable length,
 * and since these maps can change value dynamically, one could read
 * gibberish by doing partial reads while a list was changing.
 */
int cpuset_common_seq_show(struct seq_file *sf, void *v)
{
	struct cpuset *cs = css_cs(seq_css(sf));
	cpuset_filetype_t type = seq_cft(sf)->private;
	int ret = 0;

	spin_lock_irq(&callback_lock);

	switch (type) {
	case FILE_CPULIST:
		seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->cpus_allowed));
		break;
	case FILE_MEMLIST:
		seq_printf(sf, "%*pbl\n", nodemask_pr_args(&cs->mems_allowed));
		break;
	case FILE_EFFECTIVE_CPULIST:
		seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->effective_cpus));
		break;
	case FILE_EFFECTIVE_MEMLIST:
		seq_printf(sf, "%*pbl\n", nodemask_pr_args(&cs->effective_mems));
		break;
	case FILE_EXCLUSIVE_CPULIST:
		seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->exclusive_cpus));
		break;
	case FILE_EFFECTIVE_XCPULIST:
		seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->effective_xcpus));
		break;
	case FILE_SUBPARTS_CPULIST:
		seq_printf(sf, "%*pbl\n", cpumask_pr_args(subpartitions_cpus));
		break;
	case FILE_ISOLATED_CPULIST:
		seq_printf(sf, "%*pbl\n", cpumask_pr_args(isolated_cpus));
		break;
	default:
		ret = -EINVAL;
	}

	spin_unlock_irq(&callback_lock);
	return ret;
}

static int cpuset_partition_show(struct seq_file *seq, void *v)
{
	struct cpuset *cs = css_cs(seq_css(seq));
	const char *err, *type = NULL;

	switch (cs->partition_root_state) {
	case PRS_ROOT:
		seq_puts(seq, "root\n");
		break;
	case PRS_ISOLATED:
		seq_puts(seq, "isolated\n");
		break;
	case PRS_MEMBER:
		seq_puts(seq, "member\n");
		break;
	case PRS_INVALID_ROOT:
		type = "root";
		fallthrough;
	case PRS_INVALID_ISOLATED:
		if (!type)
			type = "isolated";
		err = perr_strings[READ_ONCE(cs->prs_err)];
		if (err)
			seq_printf(seq, "%s invalid (%s)\n", type, err);
		else
			seq_printf(seq, "%s invalid\n", type);
		break;
	}
	return 0;
}

static ssize_t cpuset_partition_write(struct kernfs_open_file *of, char *buf,
				     size_t nbytes, loff_t off)
{
	struct cpuset *cs = css_cs(of_css(of));
	int val;
	int retval = -ENODEV;

	buf = strstrip(buf);

	if (!strcmp(buf, "root"))
		val = PRS_ROOT;
	else if (!strcmp(buf, "member"))
		val = PRS_MEMBER;
	else if (!strcmp(buf, "isolated"))
		val = PRS_ISOLATED;
	else
		return -EINVAL;

	mutex_lock(&cpuset_top_mutex);
	cpus_read_lock();
	wait_attach_done_lock();

	if (is_cpuset_online(cs))
		retval = update_prstate(cs, val);
	cpuset_update_sd_hk_unlock();
	return retval ?: nbytes;
}

/*
 * This is currently a minimal set for the default hierarchy. It can be
 * expanded later on by migrating more features and control files from v1.
 */
static struct cftype dfl_files[] = {
	{
		.name = "cpus",
		.seq_show = cpuset_common_seq_show,
		.write = cpuset_write_resmask,
		.max_write_len = (100U + 6 * NR_CPUS),
		.private = FILE_CPULIST,
		.flags = CFTYPE_NOT_ON_ROOT,
	},

	{
		.name = "mems",
		.seq_show = cpuset_common_seq_show,
		.write = cpuset_write_resmask,
		.max_write_len = (100U + 6 * MAX_NUMNODES),
		.private = FILE_MEMLIST,
		.flags = CFTYPE_NOT_ON_ROOT,
	},

	{
		.name = "cpus.effective",
		.seq_show = cpuset_common_seq_show,
		.private = FILE_EFFECTIVE_CPULIST,
	},

	{
		.name = "mems.effective",
		.seq_show = cpuset_common_seq_show,
		.private = FILE_EFFECTIVE_MEMLIST,
	},

	{
		.name = "cpus.partition",
		.seq_show = cpuset_partition_show,
		.write = cpuset_partition_write,
		.private = FILE_PARTITION_ROOT,
		.flags = CFTYPE_NOT_ON_ROOT,
		.file_offset = offsetof(struct cpuset, partition_file),
	},

	{
		.name = "cpus.exclusive",
		.seq_show = cpuset_common_seq_show,
		.write = cpuset_write_resmask,
		.max_write_len = (100U + 6 * NR_CPUS),
		.private = FILE_EXCLUSIVE_CPULIST,
		.flags = CFTYPE_NOT_ON_ROOT,
	},

	{
		.name = "cpus.exclusive.effective",
		.seq_show = cpuset_common_seq_show,
		.private = FILE_EFFECTIVE_XCPULIST,
		.flags = CFTYPE_NOT_ON_ROOT,
	},

	{
		.name = "cpus.subpartitions",
		.seq_show = cpuset_common_seq_show,
		.private = FILE_SUBPARTS_CPULIST,
		.flags = CFTYPE_ONLY_ON_ROOT | CFTYPE_DEBUG,
	},

	{
		.name = "cpus.isolated",
		.seq_show = cpuset_common_seq_show,
		.private = FILE_ISOLATED_CPULIST,
		.flags = CFTYPE_ONLY_ON_ROOT,
	},

	{ }	/* terminate */
};


/**
 * cpuset_css_alloc - Allocate a cpuset css
 * @parent_css: Parent css of the control group that the new cpuset will be
 *              part of
 * Return: cpuset css on success, -ENOMEM on failure.
 *
 * Allocate and initialize a new cpuset css, for non-NULL @parent_css, return
 * top cpuset css otherwise.
 */
static struct cgroup_subsys_state *
cpuset_css_alloc(struct cgroup_subsys_state *parent_css)
{
	struct cpuset *cs;

	if (!parent_css)
		return &top_cpuset.css;

	cs = dup_or_alloc_cpuset(NULL);
	if (!cs)
		return ERR_PTR(-ENOMEM);

	__set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
	cpuset1_init(cs);

	/* Set CS_MEMORY_MIGRATE for default hierarchy */
	if (cpuset_v2())
		__set_bit(CS_MEMORY_MIGRATE, &cs->flags);

	return &cs->css;
}

static int cpuset_css_online(struct cgroup_subsys_state *css)
{
	struct cpuset *cs = css_cs(css);
	struct cpuset *parent = parent_cs(cs);

	if (!parent)
		return 0;

	cpuset_full_lock();
	/*
	 * For v2, clear CS_SCHED_LOAD_BALANCE if parent is isolated
	 */
	if (cpuset_v2() && !is_sched_load_balance(parent))
		clear_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);

	cpuset_inc();

	spin_lock_irq(&callback_lock);
	if (is_in_v2_mode()) {
		cpumask_copy(cs->effective_cpus, parent->effective_cpus);
		cs->effective_mems = parent->effective_mems;
	}
	spin_unlock_irq(&callback_lock);
	cpuset1_online_css(css);

	cpuset_full_unlock();
	return 0;
}

/*
 * If the cpuset being removed has its flag 'sched_load_balance'
 * enabled, then simulate turning sched_load_balance off, which
 * will call rebuild_sched_domains_locked(). That is not needed
 * in the default hierarchy where only changes in partition
 * will cause repartitioning.
 */
static void cpuset_css_offline(struct cgroup_subsys_state *css)
{
	struct cpuset *cs = css_cs(css);

	cpuset_full_lock();
	if (!cpuset_v2() && is_sched_load_balance(cs))
		cpuset_update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);

	cpuset_dec();
	cpuset_full_unlock();
}

/*
 * If a dying cpuset has the 'cpus.partition' enabled, turn it off by
 * changing it back to member to free its exclusive CPUs back to the pool to
 * be used by other online cpusets.
 */
static void cpuset_css_killed(struct cgroup_subsys_state *css)
{
	struct cpuset *cs = css_cs(css);

	cpuset_full_lock();
	/* Reset valid partition back to member */
	if (is_partition_valid(cs))
		update_prstate(cs, PRS_MEMBER);
	cpuset_update_sd_hk_unlock();
}

static void cpuset_css_free(struct cgroup_subsys_state *css)
{
	struct cpuset *cs = css_cs(css);

	free_cpuset(cs);
}

static void cpuset_bind(struct cgroup_subsys_state *root_css)
{
	mutex_lock(&cpuset_mutex);
	spin_lock_irq(&callback_lock);

	if (is_in_v2_mode()) {
		cpumask_copy(top_cpuset.cpus_allowed, cpu_possible_mask);
		cpumask_copy(top_cpuset.effective_xcpus, cpu_possible_mask);
		top_cpuset.mems_allowed = node_possible_map;
	} else {
		cpumask_copy(top_cpuset.cpus_allowed,
			     top_cpuset.effective_cpus);
		top_cpuset.mems_allowed = top_cpuset.effective_mems;
	}

	spin_unlock_irq(&callback_lock);
	mutex_unlock(&cpuset_mutex);
}

/*
 * In case the child is cloned into a cpuset different from its parent,
 * additional checks are done to see if the move is allowed.
 */
static int cpuset_can_fork(struct task_struct *task, struct css_set *cset)
{
	struct cpuset *cs = css_cs(cset->subsys[cpuset_cgrp_id]);
	bool same_cs;
	int ret;

	rcu_read_lock();
	same_cs = (cs == task_cs(current));
	rcu_read_unlock();

	if (same_cs)
		return 0;

	lockdep_assert_held(&cgroup_mutex);
	mutex_lock(&cpuset_mutex);

	/* Check to see if task is allowed in the cpuset */
	ret = cpuset_can_attach_check(cs, NULL, NULL);
	if (ret)
		goto out_unlock;

	ret = task_can_attach(task);
	if (ret)
		goto out_unlock;

	ret = security_task_setscheduler(task);
	if (ret)
		goto out_unlock;

	attach_ctx.in_progress++;
out_unlock:
	mutex_unlock(&cpuset_mutex);
	return ret;
}

static void cpuset_cancel_fork(struct task_struct *task, struct css_set *cset)
{
	struct cpuset *cs = css_cs(cset->subsys[cpuset_cgrp_id]);
	bool same_cs;

	rcu_read_lock();
	same_cs = (cs == task_cs(current));
	rcu_read_unlock();

	if (same_cs)
		return;

	dec_attach_in_progress();
}

/*
 * Make sure the new task conform to the current state of its parent,
 * which could have been changed by cpuset just after it inherits the
 * state from the parent and before it sits on the cgroup's task list.
 */
static void cpuset_fork(struct task_struct *task)
{
	struct cpuset *cs, *oldcs;

	rcu_read_lock();
	cs = task_cs(task);
	oldcs = task_cs(current);
	rcu_read_unlock();

	if (cs == oldcs) {
		if (cs == &top_cpuset)
			return;

		set_cpus_allowed_ptr(task, current->cpus_ptr);
		task->mems_allowed = current->mems_allowed;
		return;
	}

	/* CLONE_INTO_CGROUP */
	mutex_lock(&cpuset_mutex);
	guarantee_online_mems(cs, &attach_ctx.nodemask_to);
	cs->old_mems_allowed = attach_ctx.nodemask_to;

	/*
	 * Assume CPUs and memory nodes are updated
	 * A CLONE_INTO_CGROUP operation should have taken the cgroup mutex
	 * and so there shouldn't be a competing cpuset_attach() operation.
	 */
	attach_ctx.cpus_updated = attach_ctx.mems_updated = true;
	attach_ctx.task_work_queued = false;
	attach_ctx.old_cs = oldcs;
	cpuset_attach_task(cs, task);
	if (attach_ctx.task_work_queued)
		schedule_flush_migrate_mm();

	dec_attach_in_progress_locked();
	mutex_unlock(&cpuset_mutex);
}

struct cgroup_subsys cpuset_cgrp_subsys = {
	.css_alloc	= cpuset_css_alloc,
	.css_online	= cpuset_css_online,
	.css_offline	= cpuset_css_offline,
	.css_killed	= cpuset_css_killed,
	.css_free	= cpuset_css_free,
	.can_attach	= cpuset_can_attach,
	.cancel_attach	= cpuset_cancel_attach,
	.attach		= cpuset_attach,
	.bind		= cpuset_bind,
	.can_fork	= cpuset_can_fork,
	.cancel_fork	= cpuset_cancel_fork,
	.fork		= cpuset_fork,
#ifdef CONFIG_CPUSETS_V1
	.legacy_cftypes	= cpuset1_files,
#endif
	.dfl_cftypes	= dfl_files,
	.early_init	= true,
	.threaded	= true,
};

/**
 * cpuset_init - initialize cpusets at system boot
 *
 * Description: Initialize top_cpuset
 **/

int __init cpuset_init(void)
{
	BUG_ON(!alloc_cpumask_var(&top_cpuset.cpus_allowed, GFP_KERNEL));
	BUG_ON(!alloc_cpumask_var(&top_cpuset.effective_cpus, GFP_KERNEL));
	BUG_ON(!alloc_cpumask_var(&top_cpuset.effective_xcpus, GFP_KERNEL));
	BUG_ON(!alloc_cpumask_var(&top_cpuset.exclusive_cpus, GFP_KERNEL));
	BUG_ON(!zalloc_cpumask_var(&subpartitions_cpus, GFP_KERNEL));
	BUG_ON(!zalloc_cpumask_var(&isolated_cpus, GFP_KERNEL));
	BUG_ON(!zalloc_cpumask_var(&isolated_hk_cpus, GFP_KERNEL));

	cpumask_setall(top_cpuset.cpus_allowed);
	nodes_setall(top_cpuset.mems_allowed);
	cpumask_setall(top_cpuset.effective_cpus);
	cpumask_setall(top_cpuset.effective_xcpus);
	cpumask_setall(top_cpuset.exclusive_cpus);
	nodes_setall(top_cpuset.effective_mems);
	init_llist_node(&top_cpuset.attach_node);

	cpuset1_init(&top_cpuset);

	BUG_ON(!alloc_cpumask_var(&cpus_attach, GFP_KERNEL));

	if (housekeeping_enabled(HK_TYPE_DOMAIN_BOOT))
		cpumask_andnot(isolated_cpus, cpu_possible_mask,
			       housekeeping_cpumask(HK_TYPE_DOMAIN_BOOT));

	return 0;
}

static void
hotplug_update_tasks(struct cpuset *cs,
		     struct cpumask *new_cpus, nodemask_t *new_mems,
		     bool cpus_updated, bool mems_updated)
{
	/* A partition root is allowed to have empty effective cpus */
	if (cpumask_empty(new_cpus) && !is_partition_valid(cs))
		cpumask_copy(new_cpus, parent_cs(cs)->effective_cpus);
	if (nodes_empty(*new_mems))
		*new_mems = parent_cs(cs)->effective_mems;

	spin_lock_irq(&callback_lock);
	cpumask_copy(cs->effective_cpus, new_cpus);
	cs->effective_mems = *new_mems;
	spin_unlock_irq(&callback_lock);

	if (cpus_updated)
		cpuset_update_tasks_cpumask(cs, new_cpus);
	if (mems_updated)
		cpuset_update_tasks_nodemask(cs);
}

void cpuset_force_rebuild(void)
{
	force_sd_rebuild = true;
}

/**
 * cpuset_hotplug_update_tasks - update tasks in a cpuset for hotunplug
 * @cs: cpuset in interest
 * @tmp: the tmpmasks structure pointer
 *
 * Compare @cs's cpu and mem masks against top_cpuset and if some have gone
 * offline, update @cs accordingly.  If @cs ends up with no CPU or memory,
 * all its tasks are moved to the nearest ancestor with both resources.
 */
static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
{
	static cpumask_t new_cpus;
	static nodemask_t new_mems;
	bool cpus_updated;
	bool mems_updated;
	bool remote;
	int partcmd = -1;
	struct cpuset *parent;

	wait_attach_done_lock();
	parent = parent_cs(cs);
	compute_effective_cpumask(&new_cpus, cs, parent);
	compute_effective_nodemask(&new_mems, cs, parent);

	if (!tmp || !cs->partition_root_state)
		goto update_tasks;

	/*
	 * Compute effective_cpus for valid partition root, may invalidate
	 * child partition roots if necessary.
	 */
	remote = is_remote_partition(cs);
	if (remote || (is_partition_valid(cs) && is_partition_valid(parent)))
		compute_partition_effective_cpumask(cs, &new_cpus);

	if (remote && (cpumask_empty(subpartitions_cpus) ||
			(cpumask_empty(&new_cpus) &&
			 partition_is_populated(cs, NULL)))) {
		WRITE_ONCE(cs->prs_err, PERR_HOTPLUG);
		remote_partition_disable(cs, tmp);
		compute_effective_cpumask(&new_cpus, cs, parent);
		remote = false;
	}

	/*
	 * Force the partition to become invalid if either one of
	 * the following conditions hold:
	 * 1) empty effective cpus but not valid empty partition.
	 * 2) parent is invalid or doesn't grant any cpus to child
	 *    partitions.
	 * 3) subpartitions_cpus is empty.
	 */
	if (is_local_partition(cs) &&
	    (!is_partition_valid(parent) ||
	     tasks_nocpu_error(parent, cs, &new_cpus) ||
	     cpumask_empty(subpartitions_cpus)))
		partcmd = partcmd_invalidate;
	/*
	 * On the other hand, an invalid partition root may be transitioned
	 * back to a regular one with a non-empty effective xcpus.
	 */
	else if (is_partition_valid(parent) && is_partition_invalid(cs) &&
		 !cpumask_empty(cs->effective_xcpus))
		partcmd = partcmd_update;

	if (partcmd >= 0) {
		update_parent_effective_cpumask(cs, partcmd, NULL, tmp);
		if ((partcmd == partcmd_invalidate) || is_partition_valid(cs)) {
			compute_partition_effective_cpumask(cs, &new_cpus);
			cpuset_force_rebuild();
		}
	}

update_tasks:
	cpus_updated = !cpumask_equal(&new_cpus, cs->effective_cpus);
	mems_updated = !nodes_equal(new_mems, cs->effective_mems);
	if (!cpus_updated && !mems_updated)
		goto unlock;	/* Hotplug doesn't affect this cpuset */

	if (mems_updated)
		check_insane_mems_config(&new_mems);

	if (is_in_v2_mode())
		hotplug_update_tasks(cs, &new_cpus, &new_mems,
				     cpus_updated, mems_updated);
	else
		cpuset1_hotplug_update_tasks(cs, &new_cpus, &new_mems,
					    cpus_updated, mems_updated);

unlock:
	mutex_unlock(&cpuset_mutex);
}

/**
 * cpuset_handle_hotplug - handle CPU/memory hot{,un}plug for a cpuset
 *
 * This function is called after either CPU or memory configuration has
 * changed and updates cpuset accordingly.  The top_cpuset is always
 * synchronized to cpu_active_mask and N_MEMORY, which is necessary in
 * order to make cpusets transparent (of no affect) on systems that are
 * actively using CPU hotplug but making no active use of cpusets.
 *
 * Non-root cpusets are only affected by offlining.  If any CPUs or memory
 * nodes have been taken down, cpuset_hotplug_update_tasks() is invoked on
 * all descendants.
 *
 * Note that CPU offlining during suspend is ignored.  We don't modify
 * cpusets across suspend/resume cycles at all.
 *
 * CPU / memory hotplug is handled synchronously.
 */
static void cpuset_handle_hotplug(void)
{
	static DECLARE_WORK(hk_sd_work, hk_sd_workfn);
	static cpumask_t new_cpus;
	static nodemask_t new_mems;
	bool cpus_updated, mems_updated;
	bool on_dfl = is_in_v2_mode();
	struct tmpmasks tmp, *ptmp = NULL;

	if (on_dfl && !alloc_tmpmasks(&tmp))
		ptmp = &tmp;

	lockdep_assert_cpus_held();
	mutex_lock(&cpuset_mutex);

	/* fetch the available cpus/mems and find out which changed how */
	cpumask_copy(&new_cpus, cpu_active_mask);
	new_mems = node_states[N_MEMORY];

	/*
	 * If subpartitions_cpus is populated, it is likely that the check
	 * below will produce a false positive on cpus_updated when the cpu
	 * list isn't changed. It is extra work, but it is better to be safe.
	 */
	cpus_updated = !cpumask_equal(top_cpuset.effective_cpus, &new_cpus) ||
		       !cpumask_empty(subpartitions_cpus);
	mems_updated = !nodes_equal(top_cpuset.effective_mems, new_mems);

	/* For v1, synchronize cpus_allowed to cpu_active_mask */
	if (cpus_updated) {
		cpuset_force_rebuild();
		spin_lock_irq(&callback_lock);
		if (!on_dfl)
			cpumask_copy(top_cpuset.cpus_allowed, &new_cpus);
		/*
		 * Make sure that CPUs allocated to child partitions
		 * do not show up in effective_cpus. If no CPU is left,
		 * we clear the subpartitions_cpus & let the child partitions
		 * fight for the CPUs again.
		 */
		if (!cpumask_empty(subpartitions_cpus)) {
			if (cpumask_subset(&new_cpus, subpartitions_cpus)) {
				cpumask_clear(subpartitions_cpus);
			} else {
				cpumask_andnot(&new_cpus, &new_cpus,
					       subpartitions_cpus);
			}
		}
		cpumask_copy(top_cpuset.effective_cpus, &new_cpus);
		spin_unlock_irq(&callback_lock);
		/* we don't mess with cpumasks of tasks in top_cpuset */
	}

	/* synchronize mems_allowed to N_MEMORY */
	if (mems_updated) {
		spin_lock_irq(&callback_lock);
		if (!on_dfl)
			top_cpuset.mems_allowed = new_mems;
		top_cpuset.effective_mems = new_mems;
		spin_unlock_irq(&callback_lock);
		cpuset_update_tasks_nodemask(&top_cpuset);
	}

	mutex_unlock(&cpuset_mutex);

	/* if cpus or mems changed, we need to propagate to descendants */
	if (cpus_updated || mems_updated) {
		struct cpuset *cs;
		struct cgroup_subsys_state *pos_css;

		rcu_read_lock();
		cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
			if (cs == &top_cpuset || !css_tryget_online(&cs->css))
				continue;
			rcu_read_unlock();

			cpuset_hotplug_update_tasks(cs, ptmp);

			rcu_read_lock();
			css_put(&cs->css);
		}
		rcu_read_unlock();
	}

	/*
	 * rebuild_sched_domains() will always be called directly if needed
	 * to make sure that newly added or removed CPU will be reflected in
	 * the sched domains. However, if isolated partition invalidation
	 * or recreation is being done (update_housekeeping set), a work item
	 * will be queued to call housekeeping_update() to update the
	 * corresponding housekeeping cpumasks after some slight delay.
	 *
	 * We rely on WORK_STRUCT_PENDING_BIT to not requeue a work item that
	 * is still pending. Before the pending bit is cleared, the work data
	 * is copied out and work item dequeued. So it is possible to queue
	 * the work again before the hk_sd_workfn() is invoked to process the
	 * previously queued work. Since hk_sd_workfn() doesn't use the work
	 * item at all, this is not a problem.
	 */
	if (force_sd_rebuild)
		rebuild_sched_domains_cpuslocked();
	if (update_housekeeping)
		queue_work(system_dfl_wq, &hk_sd_work);

	free_tmpmasks(ptmp);
}

void cpuset_update_active_cpus(void)
{
	/*
	 * We're inside cpu hotplug critical region which usually nests
	 * inside cgroup synchronization.  Bounce actual hotplug processing
	 * to a work item to avoid reverse locking order.
	 */
	cpuset_handle_hotplug();
}

/*
 * Keep top_cpuset.mems_allowed tracking node_states[N_MEMORY].
 * Call this routine anytime after node_states[N_MEMORY] changes.
 * See cpuset_update_active_cpus() for CPU hotplug handling.
 */
static int cpuset_track_online_nodes(struct notifier_block *self,
				unsigned long action, void *arg)
{
	cpuset_handle_hotplug();
	return NOTIFY_OK;
}

/**
 * cpuset_init_smp - initialize cpus_allowed
 *
 * Description: Finish top cpuset after cpu, node maps are initialized
 */
void __init cpuset_init_smp(void)
{
	/*
	 * cpus_allowd/mems_allowed set to v2 values in the initial
	 * cpuset_bind() call will be reset to v1 values in another
	 * cpuset_bind() call when v1 cpuset is mounted.
	 */
	top_cpuset.old_mems_allowed = top_cpuset.mems_allowed;

	cpumask_copy(top_cpuset.effective_cpus, cpu_active_mask);
	top_cpuset.effective_mems = node_states[N_MEMORY];

	hotplug_node_notifier(cpuset_track_online_nodes, CPUSET_CALLBACK_PRI);

	cpuset_migrate_mm_wq = alloc_ordered_workqueue("cpuset_migrate_mm", 0);
	BUG_ON(!cpuset_migrate_mm_wq);
}

/*
 * Return cpus_allowed mask from a task's cpuset.
 */
static void __cpuset_cpus_allowed_locked(struct task_struct *tsk, struct cpumask *pmask)
{
	struct cpuset *cs;

	cs = task_cs(tsk);
	if (cs != &top_cpuset)
		guarantee_active_cpus(tsk, pmask);
	/*
	 * Tasks in the top cpuset won't get update to their cpumasks
	 * when a hotplug online/offline event happens. So we include all
	 * offline cpus in the allowed cpu list.
	 */
	if ((cs == &top_cpuset) || cpumask_empty(pmask)) {
		const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);

		/*
		 * We first exclude cpus allocated to partitions. If there is no
		 * allowable online cpu left, we fall back to all possible cpus.
		 */
		cpumask_andnot(pmask, possible_mask, subpartitions_cpus);
		if (!cpumask_intersects(pmask, cpu_active_mask))
			cpumask_copy(pmask, possible_mask);
	}
}

/**
 * cpuset_cpus_allowed_locked - return cpus_allowed mask from a task's cpuset.
 * @tsk: pointer to task_struct from which to obtain cpuset->cpus_allowed.
 * @pmask: pointer to struct cpumask variable to receive cpus_allowed set.
 *
 * Similir to cpuset_cpus_allowed() except that the caller must have acquired
 * cpuset_mutex.
 */
void cpuset_cpus_allowed_locked(struct task_struct *tsk, struct cpumask *pmask)
{
	lockdep_assert_cpuset_lock_held();
	__cpuset_cpus_allowed_locked(tsk, pmask);
}

/**
 * cpuset_cpus_allowed - return cpus_allowed mask from a task's cpuset.
 * @tsk: pointer to task_struct from which to obtain cpuset->cpus_allowed.
 * @pmask: pointer to struct cpumask variable to receive cpus_allowed set.
 *
 * Description: Returns the cpumask_var_t cpus_allowed of the cpuset
 * attached to the specified @tsk.  Guaranteed to return some non-empty
 * subset of cpu_active_mask, even if this means going outside the
 * tasks cpuset, except when the task is in the top cpuset.
 **/

void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
{
	unsigned long flags;

	spin_lock_irqsave(&callback_lock, flags);
	__cpuset_cpus_allowed_locked(tsk, pmask);
	spin_unlock_irqrestore(&callback_lock, flags);
}

/**
 * cpuset_cpus_allowed_fallback - final fallback before complete catastrophe.
 * @tsk: pointer to task_struct with which the scheduler is struggling
 *
 * Description: In the case that the scheduler cannot find an allowed cpu in
 * tsk->cpus_allowed, we fall back to task_cs(tsk)->cpus_allowed. In legacy
 * mode however, this value is the same as task_cs(tsk)->effective_cpus,
 * which will not contain a sane cpumask during cases such as cpu hotplugging.
 * This is the absolute last resort for the scheduler and it is only used if
 * _every_ other avenue has been traveled.
 *
 * Returns true if the affinity of @tsk was changed, false otherwise.
 **/

bool cpuset_cpus_allowed_fallback(struct task_struct *tsk)
{
	const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
	const struct cpumask *cs_mask;
	bool changed = false;

	rcu_read_lock();
	cs_mask = task_cs(tsk)->cpus_allowed;
	if (is_in_v2_mode() && cpumask_subset(cs_mask, possible_mask)) {
		set_cpus_allowed_force(tsk, cs_mask);
		changed = true;
	}
	rcu_read_unlock();

	/*
	 * We own tsk->cpus_allowed, nobody can change it under us.
	 *
	 * But we used cs && cs->cpus_allowed lockless and thus can
	 * race with cgroup_attach_task() or update_cpumask() and get
	 * the wrong tsk->cpus_allowed. However, both cases imply the
	 * subsequent cpuset_change_cpumask()->set_cpus_allowed_ptr()
	 * which takes task_rq_lock().
	 *
	 * If we are called after it dropped the lock we must see all
	 * changes in tsk_cs()->cpus_allowed. Otherwise we can temporary
	 * set any mask even if it is not right from task_cs() pov,
	 * the pending set_cpus_allowed_ptr() will fix things.
	 *
	 * select_fallback_rq() will fix things ups and set cpu_possible_mask
	 * if required.
	 */
	return changed;
}

/*
 * Returns the number of CPUs available for this cgroup.
 *
 * This only really works for cgroup-v2 where all the controllers are mounted
 * in the same hierarchy. If not cgroup-v2 or no cpuset controller is
 * configured it reverts to num_online_cpus().
 */
int cpuset_num_cpus(struct cgroup *cgrp)
{
	int nr = num_online_cpus();
	struct cpuset *cs;

	if (is_in_v2_mode()) {
		guard(rcu)();
		cs = css_cs(cgroup_e_css(cgrp, &cpuset_cgrp_subsys));
		if (cs)
			nr = cpumask_weight(cs->effective_cpus);
	}

	return nr;
}

void __init cpuset_init_current_mems_allowed(void)
{
	nodes_setall(current->mems_allowed);
}

/**
 * cpuset_mems_allowed - return mems_allowed mask from a tasks cpuset.
 * @tsk: pointer to task_struct from which to obtain cpuset->mems_allowed.
 *
 * Description: Returns the nodemask_t mems_allowed of the cpuset
 * attached to the specified @tsk.  Guaranteed to return some non-empty
 * subset of node_states[N_MEMORY], even if this means going outside the
 * tasks cpuset.
 **/

nodemask_t cpuset_mems_allowed(struct task_struct *tsk)
{
	nodemask_t mask;
	unsigned long flags;

	spin_lock_irqsave(&callback_lock, flags);
	guarantee_online_mems(task_cs(tsk), &mask);
	spin_unlock_irqrestore(&callback_lock, flags);

	return mask;
}

/**
 * cpuset_nodemask_valid_mems_allowed - check nodemask vs. current mems_allowed
 * @nodemask: the nodemask to be checked
 *
 * Are any of the nodes in the nodemask allowed in current->mems_allowed?
 */
int cpuset_nodemask_valid_mems_allowed(const nodemask_t *nodemask)
{
	return nodes_intersects(*nodemask, current->mems_allowed);
}

/*
 * nearest_hardwall_ancestor() - Returns the nearest mem_exclusive or
 * mem_hardwall ancestor to the specified cpuset.  Call holding
 * callback_lock.  If no ancestor is mem_exclusive or mem_hardwall
 * (an unusual configuration), then returns the root cpuset.
 */
static struct cpuset *nearest_hardwall_ancestor(struct cpuset *cs)
{
	while (!(is_mem_exclusive(cs) || is_mem_hardwall(cs)) && parent_cs(cs))
		cs = parent_cs(cs);
	return cs;
}

/*
 * cpuset_current_node_allowed - Can current task allocate on a memory node?
 * @node: is this an allowed node?
 * @gfp_mask: memory allocation flags
 *
 * If we're in interrupt, yes, we can always allocate.  If @node is set in
 * current's mems_allowed, yes.  If it's not a __GFP_HARDWALL request and this
 * node is set in the nearest hardwalled cpuset ancestor to current's cpuset,
 * yes.  If current has access to memory reserves as an oom victim, yes.
 * If the current task is PF_EXITING, yes. Otherwise, no.
 *
 * GFP_USER allocations are marked with the __GFP_HARDWALL bit,
 * and do not allow allocations outside the current tasks cpuset
 * unless the task has been OOM killed or is exiting.
 * GFP_KERNEL allocations are not so marked, so can escape to the
 * nearest enclosing hardwalled ancestor cpuset.
 *
 * Scanning up parent cpusets requires callback_lock.  The
 * page allocator only calls here with __GFP_HARDWALL bit
 * _not_ set if it's a GFP_KERNEL allocation, and all nodes in the
 * current tasks mems_allowed came up empty on the first pass over
 * the zonelist.  So only GFP_KERNEL allocations, if all nodes in the
 * cpuset are short of memory, might require taking the callback_lock.
 *
 * The first call here from mm/page_alloc:get_page_from_freelist()
 * has __GFP_HARDWALL set in gfp_mask, enforcing hardwall cpusets,
 * so no allocation on a node outside the cpuset is allowed (unless
 * in interrupt, of course).  The PF_EXITING check must therefore
 * come before the __GFP_HARDWALL check, otherwise a dying task
 * would be blocked on the fast path.
 *
 * The second pass through get_page_from_freelist() doesn't even call here for
 * GFP_ATOMIC calls.  That, and the checks below have the combined affect that:
 *	in_interrupt - any node ok (current task context irrelevant)
 *	GFP_ATOMIC   - any node ok
 *	tsk_is_oom_victim   - any node ok
 *	PF_EXITING   - any node ok (let dying task exit quickly)
 *	GFP_KERNEL   - any node in enclosing hardwalled cpuset ok
 *	GFP_USER     - only nodes in current tasks mems allowed ok.
 */
bool cpuset_current_node_allowed(int node, gfp_t gfp_mask)
{
	struct cpuset *cs;		/* current cpuset ancestors */
	bool allowed;			/* is allocation in zone z allowed? */
	unsigned long flags;

	if (in_interrupt())
		return true;
	if (node_isset(node, current->mems_allowed))
		return true;
	/*
	 * Allow tasks that have access to memory reserves because they have
	 * been OOM killed to get memory anywhere.
	 */
	if (unlikely(tsk_is_oom_victim(current)))
		return true;
	if (current->flags & PF_EXITING) /* Let dying task have memory */
		return true;
	if (gfp_mask & __GFP_HARDWALL)	/* If hardwall request, stop here */
		return false;

	if (cpuset_v2())
		return true;

	/* Not hardwall and node outside mems_allowed: scan up cpusets */
	spin_lock_irqsave(&callback_lock, flags);

	cs = nearest_hardwall_ancestor(task_cs(current));
	allowed = node_isset(node, cs->mems_allowed);

	spin_unlock_irqrestore(&callback_lock, flags);
	return allowed;
}

/**
 * cpuset_nodes_allowed - return effective_mems mask from a cgroup cpuset.
 * @cgroup: pointer to struct cgroup.
 * @mask: pointer to struct nodemask_t to be returned.
 *
 * Returns effective_mems mask from a cgroup cpuset if it is cgroup v2 and
 * has cpuset subsys. Otherwise, returns node_states[N_MEMORY].
 *
 * This function intentionally avoids taking the cpuset_mutex or callback_lock
 * when accessing effective_mems. This is because the obtained effective_mems
 * is stale immediately after the query anyway (e.g., effective_mems is updated
 * immediately after releasing the lock but before returning).
 *
 * As a result, returned @mask may be empty because cs->effective_mems can be
 * rebound during this call. Besides, nodes in @mask are not guaranteed to be
 * online due to hot plugins. Callers should check the mask for validity on
 * return based on its subsequent use.
 **/
void cpuset_nodes_allowed(struct cgroup *cgroup, nodemask_t *mask)
{
	struct cgroup_subsys_state *css;
	struct cpuset *cs;

	/*
	 * In v1, mem_cgroup and cpuset are unlikely in the same hierarchy
	 * and mems_allowed is likely to be empty even if we could get to it,
	 * so return directly to avoid taking a global lock on the empty check.
	 */
	if (!cgroup || !cpuset_v2()) {
		nodes_copy(*mask, node_states[N_MEMORY]);
		return;
	}

	css = cgroup_get_e_css(cgroup, &cpuset_cgrp_subsys);
	if (!css) {
		nodes_copy(*mask, node_states[N_MEMORY]);
		return;
	}

	/*
	 * The reference taken via cgroup_get_e_css is sufficient to
	 * protect css, but it does not imply safe accesses to effective_mems.
	 *
	 * Normally, accessing effective_mems would require the cpuset_mutex
	 * or callback_lock - but the correctness of this information is stale
	 * immediately after the query anyway. We do not acquire the lock
	 * during this process to save lock contention in exchange for racing
	 * against mems_allowed rebinds.
	 */
	cs = container_of(css, struct cpuset, css);
	nodes_copy(*mask, cs->effective_mems);
	css_put(css);
}

/**
 * cpuset_spread_node() - On which node to begin search for a page
 * @rotor: round robin rotor
 *
 * If a task is marked PFA_SPREAD_PAGE and a page cache allocation uses
 * cpuset_mem_spread_node() to determine where to start looking, spread the
 * starting node around the task's mems_allowed nodes instead of starting on
 * the local node.
 *
 * We don't have to worry about the returned node being offline
 * because "it can't happen", and even if it did, it would be ok.
 *
 * The routines calling guarantee_online_mems() are careful to
 * only set nodes in task->mems_allowed that are online.  So it
 * should not be possible for the following code to return an
 * offline node.  But if it did, that would be ok, as this routine
 * is not returning the node where the allocation must be, only
 * the node where the search should start.  The zonelist used by
 * the allocator will include all nodes.  If the slab allocator
 * is passed an offline node, it will fall back to the local node.
 * See kmem_cache_alloc_node().
 */
static int cpuset_spread_node(int *rotor)
{
	return *rotor = next_node_in(*rotor, current->mems_allowed);
}

/**
 * cpuset_mem_spread_node() - On which node to begin search for a file page
 */
int cpuset_mem_spread_node(void)
{
	if (current->cpuset_mem_spread_rotor == NUMA_NO_NODE)
		current->cpuset_mem_spread_rotor =
			node_random(&current->mems_allowed);

	return cpuset_spread_node(&current->cpuset_mem_spread_rotor);
}

/**
 * cpuset_mems_allowed_intersects - Does @tsk1's mems_allowed intersect @tsk2's?
 * @tsk1: pointer to task_struct of some task.
 * @tsk2: pointer to task_struct of some other task.
 *
 * Description: Return true if @tsk1's mems_allowed intersects the
 * mems_allowed of @tsk2.  Used by the OOM killer to determine if
 * one of the task's memory usage might impact the memory available
 * to the other.
 **/

int cpuset_mems_allowed_intersects(const struct task_struct *tsk1,
				   const struct task_struct *tsk2)
{
	return nodes_intersects(tsk1->mems_allowed, tsk2->mems_allowed);
}

/**
 * cpuset_print_current_mems_allowed - prints current's cpuset and mems_allowed
 *
 * Description: Prints current's name, cpuset name, and cached copy of its
 * mems_allowed to the kernel log.
 */
void cpuset_print_current_mems_allowed(void)
{
	struct cgroup *cgrp;

	rcu_read_lock();

	cgrp = task_cs(current)->css.cgroup;
	pr_cont(",cpuset=");
	pr_cont_cgroup_name(cgrp);
	pr_cont(",mems_allowed=%*pbl",
		nodemask_pr_args(&current->mems_allowed));

	rcu_read_unlock();
}

/* Display task mems_allowed in /proc/<pid>/status file. */
void cpuset_task_status_allowed(struct seq_file *m, struct task_struct *task)
{
	seq_printf(m, "Mems_allowed:\t%*pb\n",
		   nodemask_pr_args(&task->mems_allowed));
	seq_printf(m, "Mems_allowed_list:\t%*pbl\n",
		   nodemask_pr_args(&task->mems_allowed));
}