// SPDX-License-Identifier: GPL-2.0-only
/*
 * kernel/workqueue.c - generic async execution with shared worker pool
 *
 * Copyright (C) 2002           Ingo Molnar
 *
 *   Derived from the taskqueue/keventd code by:
 *     David Woodhouse <dwmw2@infradead.org>
 *     Andrew Morton
 *     Kai Petzke <wpp@marie.physik.tu-berlin.de>
 *     Theodore Ts'o <tytso@mit.edu>
 *
 * Made to use alloc_percpu by Christoph Lameter.
 *
 * Copyright (C) 2010           SUSE Linux Products GmbH
 * Copyright (C) 2010           Tejun Heo <tj@kernel.org>
 *
 * This is the generic async execution mechanism.  Work items as are
 * executed in process context.  The worker pool is shared and
 * automatically managed.  There are two worker pools for each CPU (one for
 * normal work items and the other for high priority ones) and some extra
 * pools for workqueues which are not bound to any specific CPU - the
 * number of these backing pools is dynamic.
 *
 * Please read Documentation/core-api/workqueue.rst for details.
 */

#include <linux/export.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/signal.h>
#include <linux/completion.h>
#include <linux/workqueue.h>
#include <linux/slab.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/kthread.h>
#include <linux/hardirq.h>
#include <linux/mempolicy.h>
#include <linux/freezer.h>
#include <linux/debug_locks.h>
#include <linux/lockdep.h>
#include <linux/idr.h>
#include <linux/jhash.h>
#include <linux/hashtable.h>
#include <linux/rculist.h>
#include <linux/nodemask.h>
#include <linux/moduleparam.h>
#include <linux/uaccess.h>
#include <linux/sched/isolation.h>
#include <linux/nmi.h>

#include "workqueue_internal.h"

enum {
        /*
         * worker_pool flags
         *
         * A bound pool is either associated or disassociated with its CPU.
         * While associated (!DISASSOCIATED), all workers are bound to the
         * CPU and none has %WORKER_UNBOUND set and concurrency management
         * is in effect.
         *
         * While DISASSOCIATED, the cpu may be offline and all workers have
         * %WORKER_UNBOUND set and concurrency management disabled, and may
         * be executing on any CPU.  The pool behaves as an unbound one.
         *
         * Note that DISASSOCIATED should be flipped only while holding
         * wq_pool_attach_mutex to avoid changing binding state while
         * worker_attach_to_pool() is in progress.
         */
        POOL_MANAGER_ACTIVE     = 1 << 0,       /* being managed */
        POOL_DISASSOCIATED      = 1 << 2,       /* cpu can't serve workers */

        /* worker flags */
        WORKER_DIE              = 1 << 1,       /* die die die */
        WORKER_IDLE             = 1 << 2,       /* is idle */
        WORKER_PREP             = 1 << 3,       /* preparing to run works */
        WORKER_CPU_INTENSIVE    = 1 << 6,       /* cpu intensive */
        WORKER_UNBOUND          = 1 << 7,       /* worker is unbound */
        WORKER_REBOUND          = 1 << 8,       /* worker was rebound */

        WORKER_NOT_RUNNING      = WORKER_PREP | WORKER_CPU_INTENSIVE |
                                  WORKER_UNBOUND | WORKER_REBOUND,

        NR_STD_WORKER_POOLS     = 2,            /* # standard pools per cpu */

        UNBOUND_POOL_HASH_ORDER = 6,            /* hashed by pool->attrs */
        BUSY_WORKER_HASH_ORDER  = 6,            /* 64 pointers */

        MAX_IDLE_WORKERS_RATIO  = 4,            /* 1/4 of busy can be idle */
        IDLE_WORKER_TIMEOUT     = 300 * HZ,     /* keep idle ones for 5 mins */

        MAYDAY_INITIAL_TIMEOUT  = HZ / 100 >= 2 ? HZ / 100 : 2,
                                                /* call for help after 10ms
                                                   (min two ticks) */
        MAYDAY_INTERVAL         = HZ / 10,      /* and then every 100ms */
        CREATE_COOLDOWN         = HZ,           /* time to breath after fail */

        /*
         * Rescue workers are used only on emergencies and shared by
         * all cpus.  Give MIN_NICE.
         */
        RESCUER_NICE_LEVEL      = MIN_NICE,
        HIGHPRI_NICE_LEVEL      = MIN_NICE,

        WQ_NAME_LEN             = 24,
};

/*
 * Structure fields follow one of the following exclusion rules.
 *
 * I: Modifiable by initialization/destruction paths and read-only for
 *    everyone else.
 *
 * P: Preemption protected.  Disabling preemption is enough and should
 *    only be modified and accessed from the local cpu.
 *
 * L: pool->lock protected.  Access with pool->lock held.
 *
 * X: During normal operation, modification requires pool->lock and should
 *    be done only from local cpu.  Either disabling preemption on local
 *    cpu or grabbing pool->lock is enough for read access.  If
 *    POOL_DISASSOCIATED is set, it's identical to L.
 *
 * A: wq_pool_attach_mutex protected.
 *
 * PL: wq_pool_mutex protected.
 *
 * PR: wq_pool_mutex protected for writes.  RCU protected for reads.
 *
 * PW: wq_pool_mutex and wq->mutex protected for writes.  Either for reads.
 *
 * PWR: wq_pool_mutex and wq->mutex protected for writes.  Either or
 *      RCU for reads.
 *
 * WQ: wq->mutex protected.
 *
 * WR: wq->mutex protected for writes.  RCU protected for reads.
 *
 * MD: wq_mayday_lock protected.
 */

/* struct worker is defined in workqueue_internal.h */

struct worker_pool {
        spinlock_t              lock;           /* the pool lock */
        int                     cpu;            /* I: the associated cpu */
        int                     node;           /* I: the associated node ID */
        int                     id;             /* I: pool ID */
        unsigned int            flags;          /* X: flags */

        unsigned long           watchdog_ts;    /* L: watchdog timestamp */

        struct list_head        worklist;       /* L: list of pending works */

        int                     nr_workers;     /* L: total number of workers */
        int                     nr_idle;        /* L: currently idle workers */

        struct list_head        idle_list;      /* X: list of idle workers */
        struct timer_list       idle_timer;     /* L: worker idle timeout */
        struct timer_list       mayday_timer;   /* L: SOS timer for workers */

        /* a workers is either on busy_hash or idle_list, or the manager */
        DECLARE_HASHTABLE(busy_hash, BUSY_WORKER_HASH_ORDER);
                                                /* L: hash of busy workers */

        struct worker           *manager;       /* L: purely informational */
        struct list_head        workers;        /* A: attached workers */
        struct completion       *detach_completion; /* all workers detached */

        struct ida              worker_ida;     /* worker IDs for task name */

        struct workqueue_attrs  *attrs;         /* I: worker attributes */
        struct hlist_node       hash_node;      /* PL: unbound_pool_hash node */
        int                     refcnt;         /* PL: refcnt for unbound pools */

        /*
         * The current concurrency level.  As it's likely to be accessed
         * from other CPUs during try_to_wake_up(), put it in a separate
         * cacheline.
         */
        atomic_t                nr_running ____cacheline_aligned_in_smp;

        /*
         * Destruction of pool is RCU protected to allow dereferences
         * from get_work_pool().
         */
        struct rcu_head         rcu;
} ____cacheline_aligned_in_smp;

/*
 * The per-pool workqueue.  While queued, the lower WORK_STRUCT_FLAG_BITS
 * of work_struct->data are used for flags and the remaining high bits
 * point to the pwq; thus, pwqs need to be aligned at two's power of the
 * number of flag bits.
 */
struct pool_workqueue {
        struct worker_pool      *pool;          /* I: the associated pool */
        struct workqueue_struct *wq;            /* I: the owning workqueue */
        int                     work_color;     /* L: current color */
        int                     flush_color;    /* L: flushing color */
        int                     refcnt;         /* L: reference count */
        int                     nr_in_flight[WORK_NR_COLORS];
                                                /* L: nr of in_flight works */
        int                     nr_active;      /* L: nr of active works */
        int                     max_active;     /* L: max active works */
        struct list_head        delayed_works;  /* L: delayed works */
        struct list_head        pwqs_node;      /* WR: node on wq->pwqs */
        struct list_head        mayday_node;    /* MD: node on wq->maydays */

        /*
         * Release of unbound pwq is punted to system_wq.  See put_pwq()
         * and pwq_unbound_release_workfn() for details.  pool_workqueue
         * itself is also RCU protected so that the first pwq can be
         * determined without grabbing wq->mutex.
         */
        struct work_struct      unbound_release_work;
        struct rcu_head         rcu;
} __aligned(1 << WORK_STRUCT_FLAG_BITS);

/*
 * Structure used to wait for workqueue flush.
 */
struct wq_flusher {
        struct list_head        list;           /* WQ: list of flushers */
        int                     flush_color;    /* WQ: flush color waiting for */
        struct completion       done;           /* flush completion */
};

struct wq_device;

/*
 * The externally visible workqueue.  It relays the issued work items to
 * the appropriate worker_pool through its pool_workqueues.
 */
struct workqueue_struct {
        struct list_head        pwqs;           /* WR: all pwqs of this wq */
        struct list_head        list;           /* PR: list of all workqueues */

        struct mutex            mutex;          /* protects this wq */
        int                     work_color;     /* WQ: current work color */
        int                     flush_color;    /* WQ: current flush color */
        atomic_t                nr_pwqs_to_flush; /* flush in progress */
        struct wq_flusher       *first_flusher; /* WQ: first flusher */
        struct list_head        flusher_queue;  /* WQ: flush waiters */
        struct list_head        flusher_overflow; /* WQ: flush overflow list */

        struct list_head        maydays;        /* MD: pwqs requesting rescue */
        struct worker           *rescuer;       /* I: rescue worker */

        int                     nr_drainers;    /* WQ: drain in progress */
        int                     saved_max_active; /* WQ: saved pwq max_active */

        struct workqueue_attrs  *unbound_attrs; /* PW: only for unbound wqs */
        struct pool_workqueue   *dfl_pwq;       /* PW: only for unbound wqs */

#ifdef CONFIG_SYSFS
        struct wq_device        *wq_dev;        /* I: for sysfs interface */
#endif
#ifdef CONFIG_LOCKDEP
        char                    *lock_name;
        struct lock_class_key   key;
        struct lockdep_map      lockdep_map;
#endif
        char                    name[WQ_NAME_LEN]; /* I: workqueue name */

        /*
         * Destruction of workqueue_struct is RCU protected to allow walking
         * the workqueues list without grabbing wq_pool_mutex.
         * This is used to dump all workqueues from sysrq.
         */
        struct rcu_head         rcu;

        /* hot fields used during command issue, aligned to cacheline */
        unsigned int            flags ____cacheline_aligned; /* WQ: WQ_* flags */
        struct pool_workqueue __percpu *cpu_pwqs; /* I: per-cpu pwqs */
        struct pool_workqueue __rcu *numa_pwq_tbl[]; /* PWR: unbound pwqs indexed by node */
};

static struct kmem_cache *pwq_cache;

static cpumask_var_t *wq_numa_possible_cpumask;
                                        /* possible CPUs of each node */

static bool wq_disable_numa;
module_param_named(disable_numa, wq_disable_numa, bool, 0444);

/* see the comment above the definition of WQ_POWER_EFFICIENT */
static bool wq_power_efficient = IS_ENABLED(CONFIG_WQ_POWER_EFFICIENT_DEFAULT);
module_param_named(power_efficient, wq_power_efficient, bool, 0444);

static bool wq_online;                  /* can kworkers be created yet? */

static bool wq_numa_enabled;            /* unbound NUMA affinity enabled */

/* buf for wq_update_unbound_numa_attrs(), protected by CPU hotplug exclusion */
static struct workqueue_attrs *wq_update_unbound_numa_attrs_buf;

static DEFINE_MUTEX(wq_pool_mutex);     /* protects pools and workqueues list */
static DEFINE_MUTEX(wq_pool_attach_mutex); /* protects worker attach/detach */
static DEFINE_SPINLOCK(wq_mayday_lock); /* protects wq->maydays list */
static DECLARE_WAIT_QUEUE_HEAD(wq_manager_wait); /* wait for manager to go away */

static LIST_HEAD(workqueues);           /* PR: list of all workqueues */
static bool workqueue_freezing;         /* PL: have wqs started freezing? */

/* PL: allowable cpus for unbound wqs and work items */
static cpumask_var_t wq_unbound_cpumask;

/* CPU where unbound work was last round robin scheduled from this CPU */
static DEFINE_PER_CPU(int, wq_rr_cpu_last);

/*
 * Local execution of unbound work items is no longer guaranteed.  The
 * following always forces round-robin CPU selection on unbound work items
 * to uncover usages which depend on it.
 */
#ifdef CONFIG_DEBUG_WQ_FORCE_RR_CPU
static bool wq_debug_force_rr_cpu = true;
#else
static bool wq_debug_force_rr_cpu = false;
#endif
module_param_named(debug_force_rr_cpu, wq_debug_force_rr_cpu, bool, 0644);

/* the per-cpu worker pools */
static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS], cpu_worker_pools);

static DEFINE_IDR(worker_pool_idr);     /* PR: idr of all pools */

/* PL: hash of all unbound pools keyed by pool->attrs */
static DEFINE_HASHTABLE(unbound_pool_hash, UNBOUND_POOL_HASH_ORDER);

/* I: attributes used when instantiating standard unbound pools on demand */
static struct workqueue_attrs *unbound_std_wq_attrs[NR_STD_WORKER_POOLS];

/* I: attributes used when instantiating ordered pools on demand */
static struct workqueue_attrs *ordered_wq_attrs[NR_STD_WORKER_POOLS];

struct workqueue_struct *system_wq __read_mostly;
EXPORT_SYMBOL(system_wq);
struct workqueue_struct *system_highpri_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_highpri_wq);
struct workqueue_struct *system_long_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_long_wq);
struct workqueue_struct *system_unbound_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_unbound_wq);
struct workqueue_struct *system_freezable_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_freezable_wq);
struct workqueue_struct *system_power_efficient_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_power_efficient_wq);
struct workqueue_struct *system_freezable_power_efficient_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_freezable_power_efficient_wq);

static int worker_thread(void *__worker);
static void workqueue_sysfs_unregister(struct workqueue_struct *wq);

#define CREATE_TRACE_POINTS
#include <trace/events/workqueue.h>

#define assert_rcu_or_pool_mutex()                                      \
        RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&                       \
                         !lockdep_is_held(&wq_pool_mutex),              \
                         "RCU or wq_pool_mutex should be held")

#define assert_rcu_or_wq_mutex(wq)                                      \
        RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&                       \
                         !lockdep_is_held(&wq->mutex),                  \
                         "RCU or wq->mutex should be held")

#define assert_rcu_or_wq_mutex_or_pool_mutex(wq)                        \
        RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&                       \
                         !lockdep_is_held(&wq->mutex) &&                \
                         !lockdep_is_held(&wq_pool_mutex),              \
                         "RCU, wq->mutex or wq_pool_mutex should be held")

#define for_each_cpu_worker_pool(pool, cpu)                             \
        for ((pool) = &per_cpu(cpu_worker_pools, cpu)[0];               \
             (pool) < &per_cpu(cpu_worker_pools, cpu)[NR_STD_WORKER_POOLS]; \
             (pool)++)

/**
 * for_each_pool - iterate through all worker_pools in the system
 * @pool: iteration cursor
 * @pi: integer used for iteration
 *
 * This must be called either with wq_pool_mutex held or RCU read
 * locked.  If the pool needs to be used beyond the locking in effect, the
 * caller is responsible for guaranteeing that the pool stays online.
 *
 * The if/else clause exists only for the lockdep assertion and can be
 * ignored.
 */
#define for_each_pool(pool, pi)                                         \
        idr_for_each_entry(&worker_pool_idr, pool, pi)                  \
                if (({ assert_rcu_or_pool_mutex(); false; })) { }       \
                else

/**
 * for_each_pool_worker - iterate through all workers of a worker_pool
 * @worker: iteration cursor
 * @pool: worker_pool to iterate workers of
 *
 * This must be called with wq_pool_attach_mutex.
 *
 * The if/else clause exists only for the lockdep assertion and can be
 * ignored.
 */
#define for_each_pool_worker(worker, pool)                              \
        list_for_each_entry((worker), &(pool)->workers, node)           \
                if (({ lockdep_assert_held(&wq_pool_attach_mutex); false; })) { } \
                else

/**
 * for_each_pwq - iterate through all pool_workqueues of the specified workqueue
 * @pwq: iteration cursor
 * @wq: the target workqueue
 *
 * This must be called either with wq->mutex held or RCU read locked.
 * If the pwq needs to be used beyond the locking in effect, the caller is
 * responsible for guaranteeing that the pwq stays online.
 *
 * The if/else clause exists only for the lockdep assertion and can be
 * ignored.
 */
#define for_each_pwq(pwq, wq)                                           \
        list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node)          \
                if (({ assert_rcu_or_wq_mutex(wq); false; })) { }       \
                else

#ifdef CONFIG_DEBUG_OBJECTS_WORK

static struct debug_obj_descr work_debug_descr;

static void *work_debug_hint(void *addr)
{
        return ((struct work_struct *) addr)->func;
}

static bool work_is_static_object(void *addr)
{
        struct work_struct *work = addr;

        return test_bit(WORK_STRUCT_STATIC_BIT, work_data_bits(work));
}

/*
 * fixup_init is called when:
 * - an active object is initialized
 */
static bool work_fixup_init(void *addr, enum debug_obj_state state)
{
        struct work_struct *work = addr;

        switch (state) {
        case ODEBUG_STATE_ACTIVE:
                cancel_work_sync(work);
                debug_object_init(work, &work_debug_descr);
                return true;
        default:
                return false;
        }
}

/*
 * fixup_free is called when:
 * - an active object is freed
 */
static bool work_fixup_free(void *addr, enum debug_obj_state state)
{
        struct work_struct *work = addr;

        switch (state) {
        case ODEBUG_STATE_ACTIVE:
                cancel_work_sync(work);
                debug_object_free(work, &work_debug_descr);
                return true;
        default:
                return false;
        }
}

static struct debug_obj_descr work_debug_descr = {
        .name           = "work_struct",
        .debug_hint     = work_debug_hint,
        .is_static_object = work_is_static_object,
        .fixup_init     = work_fixup_init,
        .fixup_free     = work_fixup_free,
};

static inline void debug_work_activate(struct work_struct *work)
{
        debug_object_activate(work, &work_debug_descr);
}

static inline void debug_work_deactivate(struct work_struct *work)
{
        debug_object_deactivate(work, &work_debug_descr);
}

void __init_work(struct work_struct *work, int onstack)
{
        if (onstack)
                debug_object_init_on_stack(work, &work_debug_descr);
        else
                debug_object_init(work, &work_debug_descr);
}
EXPORT_SYMBOL_GPL(__init_work);

void destroy_work_on_stack(struct work_struct *work)
{
        debug_object_free(work, &work_debug_descr);
}
EXPORT_SYMBOL_GPL(destroy_work_on_stack);

void destroy_delayed_work_on_stack(struct delayed_work *work)
{
        destroy_timer_on_stack(&work->timer);
        debug_object_free(&work->work, &work_debug_descr);
}
EXPORT_SYMBOL_GPL(destroy_delayed_work_on_stack);

#else
static inline void debug_work_activate(struct work_struct *work) { }
static inline void debug_work_deactivate(struct work_struct *work) { }
#endif

/**
 * worker_pool_assign_id - allocate ID and assing it to @pool
 * @pool: the pool pointer of interest
 *
 * Returns 0 if ID in [0, WORK_OFFQ_POOL_NONE) is allocated and assigned
 * successfully, -errno on failure.
 */
static int worker_pool_assign_id(struct worker_pool *pool)
{
        int ret;

        lockdep_assert_held(&wq_pool_mutex);

        ret = idr_alloc(&worker_pool_idr, pool, 0, WORK_OFFQ_POOL_NONE,
                        GFP_KERNEL);
        if (ret >= 0) {
                pool->id = ret;
                return 0;
        }
        return ret;
}

/**
 * unbound_pwq_by_node - return the unbound pool_workqueue for the given node
 * @wq: the target workqueue
 * @node: the node ID
 *
 * This must be called with any of wq_pool_mutex, wq->mutex or RCU
 * read locked.
 * If the pwq needs to be used beyond the locking in effect, the caller is
 * responsible for guaranteeing that the pwq stays online.
 *
 * Return: The unbound pool_workqueue for @node.
 */
static struct pool_workqueue *unbound_pwq_by_node(struct workqueue_struct *wq,
                                                  int node)
{
        assert_rcu_or_wq_mutex_or_pool_mutex(wq);

        /*
         * XXX: @node can be NUMA_NO_NODE if CPU goes offline while a
         * delayed item is pending.  The plan is to keep CPU -> NODE
         * mapping valid and stable across CPU on/offlines.  Once that
         * happens, this workaround can be removed.
         */
        if (unlikely(node == NUMA_NO_NODE))
                return wq->dfl_pwq;

        return rcu_dereference_raw(wq->numa_pwq_tbl[node]);
}

static unsigned int work_color_to_flags(int color)
{
        return color << WORK_STRUCT_COLOR_SHIFT;
}

static int get_work_color(struct work_struct *work)
{
        return (*work_data_bits(work) >> WORK_STRUCT_COLOR_SHIFT) &
                ((1 << WORK_STRUCT_COLOR_BITS) - 1);
}

static int work_next_color(int color)
{
        return (color + 1) % WORK_NR_COLORS;
}

/*
 * While queued, %WORK_STRUCT_PWQ is set and non flag bits of a work's data
 * contain the pointer to the queued pwq.  Once execution starts, the flag
 * is cleared and the high bits contain OFFQ flags and pool ID.
 *
 * set_work_pwq(), set_work_pool_and_clear_pending(), mark_work_canceling()
 * and clear_work_data() can be used to set the pwq, pool or clear
 * work->data.  These functions should only be called while the work is
 * owned - ie. while the PENDING bit is set.
 *
 * get_work_pool() and get_work_pwq() can be used to obtain the pool or pwq
 * corresponding to a work.  Pool is available once the work has been
 * queued anywhere after initialization until it is sync canceled.  pwq is
 * available only while the work item is queued.
 *
 * %WORK_OFFQ_CANCELING is used to mark a work item which is being
 * canceled.  While being canceled, a work item may have its PENDING set
 * but stay off timer and worklist for arbitrarily long and nobody should
 * try to steal the PENDING bit.
 */
static inline void set_work_data(struct work_struct *work, unsigned long data,
                                 unsigned long flags)
{
        WARN_ON_ONCE(!work_pending(work));
        atomic_long_set(&work->data, data | flags | work_static(work));
}

static void set_work_pwq(struct work_struct *work, struct pool_workqueue *pwq,
                         unsigned long extra_flags)
{
        set_work_data(work, (unsigned long)pwq,
                      WORK_STRUCT_PENDING | WORK_STRUCT_PWQ | extra_flags);
}

static void set_work_pool_and_keep_pending(struct work_struct *work,
                                           int pool_id)
{
        set_work_data(work, (unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT,
                      WORK_STRUCT_PENDING);
}

static void set_work_pool_and_clear_pending(struct work_struct *work,
                                            int pool_id)
{
        /*
         * The following wmb is paired with the implied mb in
         * test_and_set_bit(PENDING) and ensures all updates to @work made
         * here are visible to and precede any updates by the next PENDING
         * owner.
         */
        smp_wmb();
        set_work_data(work, (unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT, 0);
        /*
         * The following mb guarantees that previous clear of a PENDING bit
         * will not be reordered with any speculative LOADS or STORES from
         * work->current_func, which is executed afterwards.  This possible
         * reordering can lead to a missed execution on attempt to queue
         * the same @work.  E.g. consider this case:
         *
         *   CPU#0                         CPU#1
         *   ----------------------------  --------------------------------
         *
         * 1  STORE event_indicated
         * 2  queue_work_on() {
         * 3    test_and_set_bit(PENDING)
         * 4 }                             set_..._and_clear_pending() {
         * 5                                 set_work_data() # clear bit
         * 6                                 smp_mb()
         * 7                               work->current_func() {
         * 8                                  LOAD event_indicated
         *                                 }
         *
         * Without an explicit full barrier speculative LOAD on line 8 can
         * be executed before CPU#0 does STORE on line 1.  If that happens,
         * CPU#0 observes the PENDING bit is still set and new execution of
         * a @work is not queued in a hope, that CPU#1 will eventually
         * finish the queued @work.  Meanwhile CPU#1 does not see
         * event_indicated is set, because speculative LOAD was executed
         * before actual STORE.
         */
        smp_mb();
}

static void clear_work_data(struct work_struct *work)
{
        smp_wmb();      /* see set_work_pool_and_clear_pending() */
        set_work_data(work, WORK_STRUCT_NO_POOL, 0);
}

static struct pool_workqueue *get_work_pwq(struct work_struct *work)
{
        unsigned long data = atomic_long_read(&work->data);

        if (data & WORK_STRUCT_PWQ)
                return (void *)(data & WORK_STRUCT_WQ_DATA_MASK);
        else
                return NULL;
}

/**
 * get_work_pool - return the worker_pool a given work was associated with
 * @work: the work item of interest
 *
 * Pools are created and destroyed under wq_pool_mutex, and allows read
 * access under RCU read lock.  As such, this function should be
 * called under wq_pool_mutex or inside of a rcu_read_lock() region.
 *
 * All fields of the returned pool are accessible as long as the above
 * mentioned locking is in effect.  If the returned pool needs to be used
 * beyond the critical section, the caller is responsible for ensuring the
 * returned pool is and stays online.
 *
 * Return: The worker_pool @work was last associated with.  %NULL if none.
 */
static struct worker_pool *get_work_pool(struct work_struct *work)
{
        unsigned long data = atomic_long_read(&work->data);
        int pool_id;

        assert_rcu_or_pool_mutex();

        if (data & WORK_STRUCT_PWQ)
                return ((struct pool_workqueue *)
                        (data & WORK_STRUCT_WQ_DATA_MASK))->pool;

        pool_id = data >> WORK_OFFQ_POOL_SHIFT;
        if (pool_id == WORK_OFFQ_POOL_NONE)
                return NULL;

        return idr_find(&worker_pool_idr, pool_id);
}

/**
 * get_work_pool_id - return the worker pool ID a given work is associated with
 * @work: the work item of interest
 *
 * Return: The worker_pool ID @work was last associated with.
 * %WORK_OFFQ_POOL_NONE if none.
 */
static int get_work_pool_id(struct work_struct *work)
{
        unsigned long data = atomic_long_read(&work->data);

        if (data & WORK_STRUCT_PWQ)
                return ((struct pool_workqueue *)
                        (data & WORK_STRUCT_WQ_DATA_MASK))->pool->id;

        return data >> WORK_OFFQ_POOL_SHIFT;
}

static void mark_work_canceling(struct work_struct *work)
{
        unsigned long pool_id = get_work_pool_id(work);

        pool_id <<= WORK_OFFQ_POOL_SHIFT;
        set_work_data(work, pool_id | WORK_OFFQ_CANCELING, WORK_STRUCT_PENDING);
}

static bool work_is_canceling(struct work_struct *work)
{
        unsigned long data = atomic_long_read(&work->data);

        return !(data & WORK_STRUCT_PWQ) && (data & WORK_OFFQ_CANCELING);
}

/*
 * Policy functions.  These define the policies on how the global worker
 * pools are managed.  Unless noted otherwise, these functions assume that
 * they're being called with pool->lock held.
 */

static bool __need_more_worker(struct worker_pool *pool)
{
        return !atomic_read(&pool->nr_running);
}

/*
 * Need to wake up a worker?  Called from anything but currently
 * running workers.
 *
 * Note that, because unbound workers never contribute to nr_running, this
 * function will always return %true for unbound pools as long as the
 * worklist isn't empty.
 */
static bool need_more_worker(struct worker_pool *pool)
{
        return !list_empty(&pool->worklist) && __need_more_worker(pool);
}

/* Can I start working?  Called from busy but !running workers. */
static bool may_start_working(struct worker_pool *pool)
{
        return pool->nr_idle;
}

/* Do I need to keep working?  Called from currently running workers. */
static bool keep_working(struct worker_pool *pool)
{
        return !list_empty(&pool->worklist) &&
                atomic_read(&pool->nr_running) <= 1;
}

/* Do we need a new worker?  Called from manager. */
static bool need_to_create_worker(struct worker_pool *pool)
{
        return need_more_worker(pool) && !may_start_working(pool);
}

/* Do we have too many workers and should some go away? */
static bool too_many_workers(struct worker_pool *pool)
{
        bool managing = pool->flags & POOL_MANAGER_ACTIVE;
        int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
        int nr_busy = pool->nr_workers - nr_idle;

        return nr_idle > 2 && (nr_idle - 2) * MAX_IDLE_WORKERS_RATIO >= nr_busy;
}

/*
 * Wake up functions.
 */

/* Return the first idle worker.  Safe with preemption disabled */
static struct worker *first_idle_worker(struct worker_pool *pool)
{
        if (unlikely(list_empty(&pool->idle_list)))
                return NULL;

        return list_first_entry(&pool->idle_list, struct worker, entry);
}

/**
 * wake_up_worker - wake up an idle worker
 * @pool: worker pool to wake worker from
 *
 * Wake up the first idle worker of @pool.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock).
 */
static void wake_up_worker(struct worker_pool *pool)
{
        struct worker *worker = first_idle_worker(pool);

        if (likely(worker))
                wake_up_process(worker->task);
}

/**
 * wq_worker_running - a worker is running again
 * @task: task waking up
 *
 * This function is called when a worker returns from schedule()
 */
void wq_worker_running(struct task_struct *task)
{
        struct worker *worker = kthread_data(task);

        if (!worker->sleeping)
                return;
        if (!(worker->flags & WORKER_NOT_RUNNING))
                atomic_inc(&worker->pool->nr_running);
        worker->sleeping = 0;
}

/**
 * wq_worker_sleeping - a worker is going to sleep
 * @task: task going to sleep
 *
 * This function is called from schedule() when a busy worker is
 * going to sleep.
 */
void wq_worker_sleeping(struct task_struct *task)
{
        struct worker *next, *worker = kthread_data(task);
        struct worker_pool *pool;

        /*
         * Rescuers, which may not have all the fields set up like normal
         * workers, also reach here, let's not access anything before
         * checking NOT_RUNNING.
         */
        if (worker->flags & WORKER_NOT_RUNNING)
                return;

        pool = worker->pool;

        if (WARN_ON_ONCE(worker->sleeping))
                return;

        worker->sleeping = 1;
        spin_lock_irq(&pool->lock);

        /*
         * The counterpart of the following dec_and_test, implied mb,
         * worklist not empty test sequence is in insert_work().
         * Please read comment there.
         *
         * NOT_RUNNING is clear.  This means that we're bound to and
         * running on the local cpu w/ rq lock held and preemption
         * disabled, which in turn means that none else could be
         * manipulating idle_list, so dereferencing idle_list without pool
         * lock is safe.
         */
        if (atomic_dec_and_test(&pool->nr_running) &&
            !list_empty(&pool->worklist)) {
                next = first_idle_worker(pool);
                if (next)
                        wake_up_process(next->task);
        }
        spin_unlock_irq(&pool->lock);
}

/**
 * wq_worker_last_func - retrieve worker's last work function
 * @task: Task to retrieve last work function of.
 *
 * Determine the last function a worker executed. This is called from
 * the scheduler to get a worker's last known identity.
 *
 * CONTEXT:
 * spin_lock_irq(rq->lock)
 *
 * This function is called during schedule() when a kworker is going
 * to sleep. It's used by psi to identify aggregation workers during
 * dequeuing, to allow periodic aggregation to shut-off when that
 * worker is the last task in the system or cgroup to go to sleep.
 *
 * As this function doesn't involve any workqueue-related locking, it
 * only returns stable values when called from inside the scheduler's
 * queuing and dequeuing paths, when @task, which must be a kworker,
 * is guaranteed to not be processing any works.
 *
 * Return:
 * The last work function %current executed as a worker, NULL if it
 * hasn't executed any work yet.
 */
work_func_t wq_worker_last_func(struct task_struct *task)
{
        struct worker *worker = kthread_data(task);

        return worker->last_func;
}

/**
 * worker_set_flags - set worker flags and adjust nr_running accordingly
 * @worker: self
 * @flags: flags to set
 *
 * Set @flags in @worker->flags and adjust nr_running accordingly.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock)
 */
static inline void worker_set_flags(struct worker *worker, unsigned int flags)
{
        struct worker_pool *pool = worker->pool;

        WARN_ON_ONCE(worker->task != current);

        /* If transitioning into NOT_RUNNING, adjust nr_running. */
        if ((flags & WORKER_NOT_RUNNING) &&
            !(worker->flags & WORKER_NOT_RUNNING)) {
                atomic_dec(&pool->nr_running);
        }

        worker->flags |= flags;
}

/**
 * worker_clr_flags - clear worker flags and adjust nr_running accordingly
 * @worker: self
 * @flags: flags to clear
 *
 * Clear @flags in @worker->flags and adjust nr_running accordingly.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock)
 */
static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
{
        struct worker_pool *pool = worker->pool;
        unsigned int oflags = worker->flags;

        WARN_ON_ONCE(worker->task != current);

        worker->flags &= ~flags;

        /*
         * If transitioning out of NOT_RUNNING, increment nr_running.  Note
         * that the nested NOT_RUNNING is not a noop.  NOT_RUNNING is mask
         * of multiple flags, not a single flag.
         */
        if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
                if (!(worker->flags & WORKER_NOT_RUNNING))
                        atomic_inc(&pool->nr_running);
}

/**
 * find_worker_executing_work - find worker which is executing a work
 * @pool: pool of interest
 * @work: work to find worker for
 *
 * Find a worker which is executing @work on @pool by searching
 * @pool->busy_hash which is keyed by the address of @work.  For a worker

 * to match, its current execution should match the address of @work and
 * its work function.  This is to avoid unwanted dependency between
 * unrelated work executions through a work item being recycled while still
 * being executed.
 *
 * This is a bit tricky.  A work item may be freed once its execution
 * starts and nothing prevents the freed area from being recycled for
 * another work item.  If the same work item address ends up being reused
 * before the original execution finishes, workqueue will identify the
 * recycled work item as currently executing and make it wait until the
 * current execution finishes, introducing an unwanted dependency.
 *
 * This function checks the work item address and work function to avoid
 * false positives.  Note that this isn't complete as one may construct a
 * work function which can introduce dependency onto itself through a
 * recycled work item.  Well, if somebody wants to shoot oneself in the
 * foot that badly, there's only so much we can do, and if such deadlock
 * actually occurs, it should be easy to locate the culprit work function.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock).
 *
 * Return:
 * Pointer to worker which is executing @work if found, %NULL
 * otherwise.
 */
static struct worker *find_worker_executing_work(struct worker_pool *pool,
                                                 struct work_struct *work)
{
        struct worker *worker;

        hash_for_each_possible(pool->busy_hash, worker, hentry,
                               (unsigned long)work)
                if (worker->current_work == work &&
                    worker->current_func == work->func)
                        return worker;

        return NULL;
}

/**
 * move_linked_works - move linked works to a list
 * @work: start of series of works to be scheduled
 * @head: target list to append @work to
 * @nextp: out parameter for nested worklist walking
 *
 * Schedule linked works starting from @work to @head.  Work series to
 * be scheduled starts at @work and includes any consecutive work with
 * WORK_STRUCT_LINKED set in its predecessor.
 *
 * If @nextp is not NULL, it's updated to point to the next work of
 * the last scheduled work.  This allows move_linked_works() to be
 * nested inside outer list_for_each_entry_safe().
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock).
 */
static void move_linked_works(struct work_struct *work, struct list_head *head,
                              struct work_struct **nextp)
{
        struct work_struct *n;

        /*
         * Linked worklist will always end before the end of the list,
         * use NULL for list head.
         */
        list_for_each_entry_safe_from(work, n, NULL, entry) {
                list_move_tail(&work->entry, head);
                if (!(*work_data_bits(work) & WORK_STRUCT_LINKED))
                        break;
        }

        /*
         * If we're already inside safe list traversal and have moved
         * multiple works to the scheduled queue, the next position
         * needs to be updated.
         */
        if (nextp)
                *nextp = n;
}

/**
 * get_pwq - get an extra reference on the specified pool_workqueue
 * @pwq: pool_workqueue to get
 *
 * Obtain an extra reference on @pwq.  The caller should guarantee that
 * @pwq has positive refcnt and be holding the matching pool->lock.
 */
static void get_pwq(struct pool_workqueue *pwq)
{
        lockdep_assert_held(&pwq->pool->lock);
        WARN_ON_ONCE(pwq->refcnt <= 0);
        pwq->refcnt++;
}

/**
 * put_pwq - put a pool_workqueue reference
 * @pwq: pool_workqueue to put
 *
 * Drop a reference of @pwq.  If its refcnt reaches zero, schedule its
 * destruction.  The caller should be holding the matching pool->lock.
 */
static void put_pwq(struct pool_workqueue *pwq)
{
        lockdep_assert_held(&pwq->pool->lock);
        if (likely(--pwq->refcnt))
                return;
        if (WARN_ON_ONCE(!(pwq->wq->flags & WQ_UNBOUND)))
                return;
        /*
         * @pwq can't be released under pool->lock, bounce to
         * pwq_unbound_release_workfn().  This never recurses on the same
         * pool->lock as this path is taken only for unbound workqueues and
         * the release work item is scheduled on a per-cpu workqueue.  To
         * avoid lockdep warning, unbound pool->locks are given lockdep
         * subclass of 1 in get_unbound_pool().
         */
        schedule_work(&pwq->unbound_release_work);
}

/**
 * put_pwq_unlocked - put_pwq() with surrounding pool lock/unlock
 * @pwq: pool_workqueue to put (can be %NULL)
 *
 * put_pwq() with locking.  This function also allows %NULL @pwq.
 */
static void put_pwq_unlocked(struct pool_workqueue *pwq)
{
        if (pwq) {
                /*
                 * As both pwqs and pools are RCU protected, the
                 * following lock operations are safe.
                 */
                spin_lock_irq(&pwq->pool->lock);
                put_pwq(pwq);
                spin_unlock_irq(&pwq->pool->lock);
        }
}

static void pwq_activate_delayed_work(struct work_struct *work)
{
        struct pool_workqueue *pwq = get_work_pwq(work);

        trace_workqueue_activate_work(work);
        if (list_empty(&pwq->pool->worklist))
                pwq->pool->watchdog_ts = jiffies;
        move_linked_works(work, &pwq->pool->worklist, NULL);
        __clear_bit(WORK_STRUCT_DELAYED_BIT, work_data_bits(work));
        pwq->nr_active++;
}

static void pwq_activate_first_delayed(struct pool_workqueue *pwq)
{
        struct work_struct *work = list_first_entry(&pwq->delayed_works,
                                                    struct work_struct, entry);

        pwq_activate_delayed_work(work);
}

/**
 * pwq_dec_nr_in_flight - decrement pwq's nr_in_flight
 * @pwq: pwq of interest
 * @color: color of work which left the queue
 *
 * A work either has completed or is removed from pending queue,
 * decrement nr_in_flight of its pwq and handle workqueue flushing.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock).
 */
static void pwq_dec_nr_in_flight(struct pool_workqueue *pwq, int color)
{
        /* uncolored work items don't participate in flushing or nr_active */
        if (color == WORK_NO_COLOR)
                goto out_put;

        pwq->nr_in_flight[color]--;

        pwq->nr_active--;
        if (!list_empty(&pwq->delayed_works)) {
                /* one down, submit a delayed one */
                if (pwq->nr_active < pwq->max_active)
                        pwq_activate_first_delayed(pwq);
        }

        /* is flush in progress and are we at the flushing tip? */
        if (likely(pwq->flush_color != color))
                goto out_put;

        /* are there still in-flight works? */
        if (pwq->nr_in_flight[color])
                goto out_put;

        /* this pwq is done, clear flush_color */
        pwq->flush_color = -1;

        /*
         * If this was the last pwq, wake up the first flusher.  It
         * will handle the rest.
         */
        if (atomic_dec_and_test(&pwq->wq->nr_pwqs_to_flush))
                complete(&pwq->wq->first_flusher->done);
out_put:
        put_pwq(pwq);
}

/**
 * try_to_grab_pending - steal work item from worklist and disable irq
 * @work: work item to steal
 * @is_dwork: @work is a delayed_work
 * @flags: place to store irq state
 *
 * Try to grab PENDING bit of @work.  This function can handle @work in any
 * stable state - idle, on timer or on worklist.
 *
 * Return:
 *  1           if @work was pending and we successfully stole PENDING
 *  0           if @work was idle and we claimed PENDING
 *  -EAGAIN     if PENDING couldn't be grabbed at the moment, safe to busy-retry
 *  -ENOENT     if someone else is canceling @work, this state may persist
 *              for arbitrarily long
 *
 * Note:
 * On >= 0 return, the caller owns @work's PENDING bit.  To avoid getting
 * interrupted while holding PENDING and @work off queue, irq must be
 * disabled on entry.  This, combined with delayed_work->timer being
 * irqsafe, ensures that we return -EAGAIN for finite short period of time.
 *
 * On successful return, >= 0, irq is disabled and the caller is
 * responsible for releasing it using local_irq_restore(*@flags).
 *
 * This function is safe to call from any context including IRQ handler.
 */
static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
                               unsigned long *flags)
{
        struct worker_pool *pool;
        struct pool_workqueue *pwq;

        local_irq_save(*flags);

        /* try to steal the timer if it exists */
        if (is_dwork) {
                struct delayed_work *dwork = to_delayed_work(work);

                /*
                 * dwork->timer is irqsafe.  If del_timer() fails, it's
                 * guaranteed that the timer is not queued anywhere and not
                 * running on the local CPU.
                 */
                if (likely(del_timer(&dwork->timer)))
                        return 1;
        }

        /* try to claim PENDING the normal way */
        if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)))
                return 0;

        rcu_read_lock();
        /*
         * The queueing is in progress, or it is already queued. Try to
         * steal it from ->worklist without clearing WORK_STRUCT_PENDING.
         */
        pool = get_work_pool(work);
        if (!pool)
                goto fail;

        spin_lock(&pool->lock);
        /*
         * work->data is guaranteed to point to pwq only while the work
         * item is queued on pwq->wq, and both updating work->data to point
         * to pwq on queueing and to pool on dequeueing are done under
         * pwq->pool->lock.  This in turn guarantees that, if work->data
         * points to pwq which is associated with a locked pool, the work
         * item is currently queued on that pool.
         */
        pwq = get_work_pwq(work);
        if (pwq && pwq->pool == pool) {
                debug_work_deactivate(work);

                /*
                 * A delayed work item cannot be grabbed directly because
                 * it might have linked NO_COLOR work items which, if left
                 * on the delayed_list, will confuse pwq->nr_active
                 * management later on and cause stall.  Make sure the work
                 * item is activated before grabbing.
                 */
                if (*work_data_bits(work) & WORK_STRUCT_DELAYED)
                        pwq_activate_delayed_work(work);

                list_del_init(&work->entry);
                pwq_dec_nr_in_flight(pwq, get_work_color(work));

                /* work->data points to pwq iff queued, point to pool */
                set_work_pool_and_keep_pending(work, pool->id);

                spin_unlock(&pool->lock);
                rcu_read_unlock();
                return 1;
        }
        spin_unlock(&pool->lock);
fail:
        rcu_read_unlock();
        local_irq_restore(*flags);
        if (work_is_canceling(work))
                return -ENOENT;
        cpu_relax();
        return -EAGAIN;
}

/**
 * insert_work - insert a work into a pool
 * @pwq: pwq @work belongs to
 * @work: work to insert
 * @head: insertion point
 * @extra_flags: extra WORK_STRUCT_* flags to set
 *
 * Insert @work which belongs to @pwq after @head.  @extra_flags is or'd to
 * work_struct flags.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock).
 */
static void insert_work(struct pool_workqueue *pwq, struct work_struct *work,
                        struct list_head *head, unsigned int extra_flags)
{
        struct worker_pool *pool = pwq->pool;

        /* we own @work, set data and link */
        set_work_pwq(work, pwq, extra_flags);
        list_add_tail(&work->entry, head);
        get_pwq(pwq);

        /*
         * Ensure either wq_worker_sleeping() sees the above
         * list_add_tail() or we see zero nr_running to avoid workers lying
         * around lazily while there are works to be processed.
         */
        smp_mb();

        if (__need_more_worker(pool))
                wake_up_worker(pool);
}

/*
 * Test whether @work is being queued from another work executing on the
 * same workqueue.
 */
static bool is_chained_work(struct workqueue_struct *wq)
{
        struct worker *worker;

        worker = current_wq_worker();
        /*
         * Return %true iff I'm a worker executing a work item on @wq.  If
         * I'm @worker, it's safe to dereference it without locking.
         */
        return worker && worker->current_pwq->wq == wq;
}

/*
 * When queueing an unbound work item to a wq, prefer local CPU if allowed
 * by wq_unbound_cpumask.  Otherwise, round robin among the allowed ones to
 * avoid perturbing sensitive tasks.
 */
static int wq_select_unbound_cpu(int cpu)
{
        static bool printed_dbg_warning;
        int new_cpu;

        if (likely(!wq_debug_force_rr_cpu)) {
                if (cpumask_test_cpu(cpu, wq_unbound_cpumask))
                        return cpu;
        } else if (!printed_dbg_warning) {
                pr_warn("workqueue: round-robin CPU selection forced, expect performance impact\n");
                printed_dbg_warning = true;
        }

        if (cpumask_empty(wq_unbound_cpumask))
                return cpu;

        new_cpu = __this_cpu_read(wq_rr_cpu_last);
        new_cpu = cpumask_next_and(new_cpu, wq_unbound_cpumask, cpu_online_mask);
        if (unlikely(new_cpu >= nr_cpu_ids)) {
                new_cpu = cpumask_first_and(wq_unbound_cpumask, cpu_online_mask);
                if (unlikely(new_cpu >= nr_cpu_ids))
                        return cpu;
        }
        __this_cpu_write(wq_rr_cpu_last, new_cpu);

        return new_cpu;
}

static void __queue_work(int cpu, struct workqueue_struct *wq,
                         struct work_struct *work)
{
        struct pool_workqueue *pwq;
        struct worker_pool *last_pool;
        struct list_head *worklist;
        unsigned int work_flags;
        unsigned int req_cpu = cpu;

        /*
         * While a work item is PENDING && off queue, a task trying to
         * steal the PENDING will busy-loop waiting for it to either get
         * queued or lose PENDING.  Grabbing PENDING and queueing should
         * happen with IRQ disabled.
         */
        lockdep_assert_irqs_disabled();

        debug_work_activate(work);

        /* if draining, only works from the same workqueue are allowed */
        if (unlikely(wq->flags & __WQ_DRAINING) &&
            WARN_ON_ONCE(!is_chained_work(wq)))
                return;
        rcu_read_lock();
retry:
        if (req_cpu == WORK_CPU_UNBOUND)
                cpu = wq_select_unbound_cpu(raw_smp_processor_id());

        /* pwq which will be used unless @work is executing elsewhere */
        if (!(wq->flags & WQ_UNBOUND))
                pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
        else
                pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));

        /*
         * If @work was previously on a different pool, it might still be
         * running there, in which case the work needs to be queued on that
         * pool to guarantee non-reentrancy.
         */
        last_pool = get_work_pool(work);
        if (last_pool && last_pool != pwq->pool) {
                struct worker *worker;

                spin_lock(&last_pool->lock);

                worker = find_worker_executing_work(last_pool, work);

                if (worker && worker->current_pwq->wq == wq) {
                        pwq = worker->current_pwq;
                } else {
                        /* meh... not running there, queue here */
                        spin_unlock(&last_pool->lock);
                        spin_lock(&pwq->pool->lock);
                }
        } else {
                spin_lock(&pwq->pool->lock);
        }

        /*
         * pwq is determined and locked.  For unbound pools, we could have
         * raced with pwq release and it could already be dead.  If its
         * refcnt is zero, repeat pwq selection.  Note that pwqs never die
         * without another pwq replacing it in the numa_pwq_tbl or while
         * work items are executing on it, so the retrying is guaranteed to
         * make forward-progress.
         */
        if (unlikely(!pwq->refcnt)) {
                if (wq->flags & WQ_UNBOUND) {
                        spin_unlock(&pwq->pool->lock);
                        cpu_relax();
                        goto retry;
                }
                /* oops */
                WARN_ONCE(true, "workqueue: per-cpu pwq for %s on cpu%d has 0 refcnt",
                          wq->name, cpu);
        }

        /* pwq determined, queue */
        trace_workqueue_queue_work(req_cpu, pwq, work);

        if (WARN_ON(!list_empty(&work->entry)))
                goto out;

        pwq->nr_in_flight[pwq->work_color]++;
        work_flags = work_color_to_flags(pwq->work_color);

        if (likely(pwq->nr_active < pwq->max_active)) {
                trace_workqueue_activate_work(work);
                pwq->nr_active++;
                worklist = &pwq->pool->worklist;
                if (list_empty(worklist))
                        pwq->pool->watchdog_ts = jiffies;
        } else {
                work_flags |= WORK_STRUCT_DELAYED;
                worklist = &pwq->delayed_works;
        }

        insert_work(pwq, work, worklist, work_flags);

out:
        spin_unlock(&pwq->pool->lock);
        rcu_read_unlock();
}

/**
 * queue_work_on - queue work on specific cpu
 * @cpu: CPU number to execute work on
 * @wq: workqueue to use
 * @work: work to queue
 *
 * We queue the work to a specific CPU, the caller must ensure it
 * can't go away.
 *
 * Return: %false if @work was already on a queue, %true otherwise.
 */
bool queue_work_on(int cpu, struct workqueue_struct *wq,
                   struct work_struct *work)
{
        bool ret = false;
        unsigned long flags;

        local_irq_save(flags);

        if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
                __queue_work(cpu, wq, work);
                ret = true;
        }

        local_irq_restore(flags);
        return ret;
}
EXPORT_SYMBOL(queue_work_on);

/**
 * workqueue_select_cpu_near - Select a CPU based on NUMA node
 * @node: NUMA node ID that we want to select a CPU from
 *
 * This function will attempt to find a "random" cpu available on a given
 * node. If there are no CPUs available on the given node it will return
 * WORK_CPU_UNBOUND indicating that we should just schedule to any
 * available CPU if we need to schedule this work.
 */
static int workqueue_select_cpu_near(int node)
{
        int cpu;

        /* No point in doing this if NUMA isn't enabled for workqueues */
        if (!wq_numa_enabled)
                return WORK_CPU_UNBOUND;

        /* Delay binding to CPU if node is not valid or online */
        if (node < 0 || node >= MAX_NUMNODES || !node_online(node))
                return WORK_CPU_UNBOUND;

        /* Use local node/cpu if we are already there */
        cpu = raw_smp_processor_id();
        if (node == cpu_to_node(cpu))
                return cpu;

        /* Use "random" otherwise know as "first" online CPU of node */
        cpu = cpumask_any_and(cpumask_of_node(node), cpu_online_mask);

        /* If CPU is valid return that, otherwise just defer */
        return cpu < nr_cpu_ids ? cpu : WORK_CPU_UNBOUND;
}

/**
 * queue_work_node - queue work on a "random" cpu for a given NUMA node
 * @node: NUMA node that we are targeting the work for
 * @wq: workqueue to use
 * @work: work to queue
 *
 * We queue the work to a "random" CPU within a given NUMA node. The basic
 * idea here is to provide a way to somehow associate work with a given
 * NUMA node.
 *
 * This function will only make a best effort attempt at getting this onto
 * the right NUMA node. If no node is requested or the requested node is
 * offline then we just fall back to standard queue_work behavior.
 *
 * Currently the "random" CPU ends up being the first available CPU in the
 * intersection of cpu_online_mask and the cpumask of the node, unless we
 * are running on the node. In that case we just use the current CPU.
 *
 * Return: %false if @work was already on a queue, %true otherwise.
 */
bool queue_work_node(int node, struct workqueue_struct *wq,
                     struct work_struct *work)
{
        unsigned long flags;
        bool ret = false;

        /*
         * This current implementation is specific to unbound workqueues.
         * Specifically we only return the first available CPU for a given
         * node instead of cycling through individual CPUs within the node.
         *
         * If this is used with a per-cpu workqueue then the logic in
         * workqueue_select_cpu_near would need to be updated to allow for
         * some round robin type logic.
         */
        WARN_ON_ONCE(!(wq->flags & WQ_UNBOUND));

        local_irq_save(flags);

        if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
                int cpu = workqueue_select_cpu_near(node);

                __queue_work(cpu, wq, work);
                ret = true;
        }

        local_irq_restore(flags);
        return ret;
}
EXPORT_SYMBOL_GPL(queue_work_node);

void delayed_work_timer_fn(struct timer_list *t)
{
        struct delayed_work *dwork = from_timer(dwork, t, timer);

        /* should have been called from irqsafe timer with irq already off */
        __queue_work(dwork->cpu, dwork->wq, &dwork->work);
}
EXPORT_SYMBOL(delayed_work_timer_fn);

static void __queue_delayed_work(int cpu, struct workqueue_struct *wq,
                                struct delayed_work *dwork, unsigned long delay)
{
        struct timer_list *timer = &dwork->timer;
        struct work_struct *work = &dwork->work;

        WARN_ON_ONCE(!wq);
        WARN_ON_ONCE(timer->function != delayed_work_timer_fn);
        WARN_ON_ONCE(timer_pending(timer));
        WARN_ON_ONCE(!list_empty(&work->entry));

        /*
         * If @delay is 0, queue @dwork->work immediately.  This is for
         * both optimization and correctness.  The earliest @timer can
         * expire is on the closest next tick and delayed_work users depend
         * on that there's no such delay when @delay is 0.
         */
        if (!delay) {
                __queue_work(cpu, wq, &dwork->work);
                return;
        }

        dwork->wq = wq;
        dwork->cpu = cpu;
        timer->expires = jiffies + delay;

        if (unlikely(cpu != WORK_CPU_UNBOUND))
                add_timer_on(timer, cpu);
        else
                add_timer(timer);
}

/**
 * queue_delayed_work_on - queue work on specific CPU after delay
 * @cpu: CPU number to execute work on
 * @wq: workqueue to use
 * @dwork: work to queue
 * @delay: number of jiffies to wait before queueing
 *
 * Return: %false if @work was already on a queue, %true otherwise.  If
 * @delay is zero and @dwork is idle, it will be scheduled for immediate
 * execution.
 */
bool queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
                           struct delayed_work *dwork, unsigned long delay)
{
        struct work_struct *work = &dwork->work;
        bool ret = false;
        unsigned long flags;

        /* read the comment in __queue_work() */
        local_irq_save(flags);

        if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
                __queue_delayed_work(cpu, wq, dwork, delay);
                ret = true;
        }

        local_irq_restore(flags);
        return ret;
}
EXPORT_SYMBOL(queue_delayed_work_on);

/**
 * mod_delayed_work_on - modify delay of or queue a delayed work on specific CPU
 * @cpu: CPU number to execute work on
 * @wq: workqueue to use
 * @dwork: work to queue
 * @delay: number of jiffies to wait before queueing
 *
 * If @dwork is idle, equivalent to queue_delayed_work_on(); otherwise,
 * modify @dwork's timer so that it expires after @delay.  If @delay is
 * zero, @work is guaranteed to be scheduled immediately regardless of its
 * current state.
 *
 * Return: %false if @dwork was idle and queued, %true if @dwork was
 * pending and its timer was modified.
 *
 * This function is safe to call from any context including IRQ handler.
 * See try_to_grab_pending() for details.
 */
bool mod_delayed_work_on(int cpu, struct workqueue_struct *wq,
                         struct delayed_work *dwork, unsigned long delay)
{
        unsigned long flags;
        int ret;

        do {
                ret = try_to_grab_pending(&dwork->work, true, &flags);
        } while (unlikely(ret == -EAGAIN));

        if (likely(ret >= 0)) {
                __queue_delayed_work(cpu, wq, dwork, delay);
                local_irq_restore(flags);
        }

        /* -ENOENT from try_to_grab_pending() becomes %true */
        return ret;
}
EXPORT_SYMBOL_GPL(mod_delayed_work_on);

static void rcu_work_rcufn(struct rcu_head *rcu)
{
        struct rcu_work *rwork = container_of(rcu, struct rcu_work, rcu);

        /* read the comment in __queue_work() */
        local_irq_disable();
        __queue_work(WORK_CPU_UNBOUND, rwork->wq, &rwork->work);
        local_irq_enable();
}

/**
 * queue_rcu_work - queue work after a RCU grace period
 * @wq: workqueue to use
 * @rwork: work to queue
 *
 * Return: %false if @rwork was already pending, %true otherwise.  Note
 * that a full RCU grace period is guaranteed only after a %true return.
 * While @rwork is guaranteed to be executed after a %false return, the
 * execution may happen before a full RCU grace period has passed.
 */
bool queue_rcu_work(struct workqueue_struct *wq, struct rcu_work *rwork)
{
        struct work_struct *work = &rwork->work;

        if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
                rwork->wq = wq;
                call_rcu(&rwork->rcu, rcu_work_rcufn);
                return true;
        }

        return false;
}
EXPORT_SYMBOL(queue_rcu_work);

/**
 * worker_enter_idle - enter idle state
 * @worker: worker which is entering idle state
 *
 * @worker is entering idle state.  Update stats and idle timer if
 * necessary.
 *
 * LOCKING:
 * spin_lock_irq(pool->lock).
 */
static void worker_enter_idle(struct worker *worker)
{
        struct worker_pool *pool = worker->pool;

        if (WARN_ON_ONCE(worker->flags & WORKER_IDLE) ||
            WARN_ON_ONCE(!list_empty(&worker->entry) &&
                         (worker->hentry.next || worker->hentry.pprev)))
                return;

        /* can't use worker_set_flags(), also called from create_worker() */
        worker->flags |= WORKER_IDLE;
        pool->nr_idle++;
        worker->last_active = jiffies;

        /* idle_list is LIFO */
        list_add(&worker->entry, &pool->idle_list);

        if (too_many_workers(pool) && !timer_pending(&pool->idle_timer))
                mod_timer(&pool->idle_timer, jiffies + IDLE_WORKER_TIMEOUT);

        /*
         * Sanity check nr_running.  Because unbind_workers() releases
         * pool->lock between setting %WORKER_UNBOUND and zapping
         * nr_running, the warning may trigger spuriously.  Check iff
         * unbind is not in progress.
         */
        WARN_ON_ONCE(!(pool->flags & POOL_DISASSOCIATED) &&
                     pool->nr_workers == pool->nr_idle &&
                     atomic_read(&pool->nr_running));
}

/**
 * worker_leave_idle - leave idle state
 * @worker: worker which is leaving idle state
 *
 * @worker is leaving idle state.  Update stats.
 *
 * LOCKING:
 * spin_lock_irq(pool->lock).
 */
static void worker_leave_idle(struct worker *worker)
{
        struct worker_pool *pool = worker->pool;

        if (WARN_ON_ONCE(!(worker->flags & WORKER_IDLE)))
                return;
        worker_clr_flags(worker, WORKER_IDLE);
        pool->nr_idle--;
        list_del_init(&worker->entry);
}

static struct worker *alloc_worker(int node)
{
        struct worker *worker;

        worker = kzalloc_node(sizeof(*worker), GFP_KERNEL, node);
        if (worker) {
                INIT_LIST_HEAD(&worker->entry);
                INIT_LIST_HEAD(&worker->scheduled);
                INIT_LIST_HEAD(&worker->node);
                /* on creation a worker is in !idle && prep state */
                worker->flags = WORKER_PREP;
        }
        return worker;
}

/**
 * worker_attach_to_pool() - attach a worker to a pool
 * @worker: worker to be attached
 * @pool: the target pool
 *
 * Attach @worker to @pool.  Once attached, the %WORKER_UNBOUND flag and
 * cpu-binding of @worker are kept coordinated with the pool across
 * cpu-[un]hotplugs.
 */
static void worker_attach_to_pool(struct worker *worker,
                                   struct worker_pool *pool)
{
        mutex_lock(&wq_pool_attach_mutex);

        /*
         * set_cpus_allowed_ptr() will fail if the cpumask doesn't have any
         * online CPUs.  It'll be re-applied when any of the CPUs come up.
         */
        set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);

        /*
         * The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains
         * stable across this function.  See the comments above the flag
         * definition for details.
         */
        if (pool->flags & POOL_DISASSOCIATED)
                worker->flags |= WORKER_UNBOUND;

        list_add_tail(&worker->node, &pool->workers);
        worker->pool = pool;

        mutex_unlock(&wq_pool_attach_mutex);
}

/**
 * worker_detach_from_pool() - detach a worker from its pool
 * @worker: worker which is attached to its pool
 *
 * Undo the attaching which had been done in worker_attach_to_pool().  The
 * caller worker shouldn't access to the pool after detached except it has
 * other reference to the pool.
 */
static void worker_detach_from_pool(struct worker *worker)
{
        struct worker_pool *pool = worker->pool;
        struct completion *detach_completion = NULL;

        mutex_lock(&wq_pool_attach_mutex);

        list_del(&worker->node);
        worker->pool = NULL;

        if (list_empty(&pool->workers))
                detach_completion = pool->detach_completion;
        mutex_unlock(&wq_pool_attach_mutex);

        /* clear leftover flags without pool->lock after it is detached */
        worker->flags &= ~(WORKER_UNBOUND | WORKER_REBOUND);

        if (detach_completion)
                complete(detach_completion);
}

/**
 * create_worker - create a new workqueue worker
 * @pool: pool the new worker will belong to
 *
 * Create and start a new worker which is attached to @pool.
 *
 * CONTEXT:
 * Might sleep.  Does GFP_KERNEL allocations.
 *
 * Return:
 * Pointer to the newly created worker.
 */
static struct worker *create_worker(struct worker_pool *pool)
{
        struct worker *worker = NULL;
        int id = -1;
        char id_buf[16];

        /* ID is needed to determine kthread name */
        id = ida_simple_get(&pool->worker_ida, 0, 0, GFP_KERNEL);
        if (id < 0)
                goto fail;

        worker = alloc_worker(pool->node);
        if (!worker)
                goto fail;

        worker->id = id;

        if (pool->cpu >= 0)
                snprintf(id_buf, sizeof(id_buf), "%d:%d%s", pool->cpu, id,
                         pool->attrs->nice < 0  ? "H" : "");
        else
                snprintf(id_buf, sizeof(id_buf), "u%d:%d", pool->id, id);

        worker->task = kthread_create_on_node(worker_thread, worker, pool->node,
                                              "kworker/%s", id_buf);
        if (IS_ERR(worker->task))
                goto fail;

        set_user_nice(worker->task, pool->attrs->nice);
        kthread_bind_mask(worker->task, pool->attrs->cpumask);

        /* successful, attach the worker to the pool */
        worker_attach_to_pool(worker, pool);

        /* start the newly created worker */
        spin_lock_irq(&pool->lock);
        worker->pool->nr_workers++;
        worker_enter_idle(worker);
        wake_up_process(worker->task);
        spin_unlock_irq(&pool->lock);

        return worker;

fail:
        if (id >= 0)
                ida_simple_remove(&pool->worker_ida, id);
        kfree(worker);
        return NULL;
}

/**
 * destroy_worker - destroy a workqueue worker
 * @worker: worker to be destroyed
 *
 * Destroy @worker and adjust @pool stats accordingly.  The worker should
 * be idle.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock).
 */
static void destroy_worker(struct worker *worker)
{
        struct worker_pool *pool = worker->pool;

        lockdep_assert_held(&pool->lock);

        /* sanity check frenzy */
        if (WARN_ON(worker->current_work) ||
            WARN_ON(!list_empty(&worker->scheduled)) ||
            WARN_ON(!(worker->flags & WORKER_IDLE)))
                return;

        pool->nr_workers--;
        pool->nr_idle--;

        list_del_init(&worker->entry);
        worker->flags |= WORKER_DIE;
        wake_up_process(worker->task);
}

static void idle_worker_timeout(struct timer_list *t)
{
        struct worker_pool *pool = from_timer(pool, t, idle_timer);

        spin_lock_irq(&pool->lock);

        while (too_many_workers(pool)) {
                struct worker *worker;
                unsigned long expires;

                /* idle_list is kept in LIFO order, check the last one */
                worker = list_entry(pool->idle_list.prev, struct worker, entry);
                expires = worker->last_active + IDLE_WORKER_TIMEOUT;

                if (time_before(jiffies, expires)) {

                        mod_timer(&pool->idle_timer, expires);
                        break;
                }

                destroy_worker(worker);
        }

        spin_unlock_irq(&pool->lock);
}

static void send_mayday(struct work_struct *work)
{
        struct pool_workqueue *pwq = get_work_pwq(work);
        struct workqueue_struct *wq = pwq->wq;

        lockdep_assert_held(&wq_mayday_lock);

        if (!wq->rescuer)
                return;

        /* mayday mayday mayday */
        if (list_empty(&pwq->mayday_node)) {
                /*
                 * If @pwq is for an unbound wq, its base ref may be put at
                 * any time due to an attribute change.  Pin @pwq until the
                 * rescuer is done with it.
                 */
                get_pwq(pwq);
                list_add_tail(&pwq->mayday_node, &wq->maydays);
                wake_up_process(wq->rescuer->task);
        }
}

static void pool_mayday_timeout(struct timer_list *t)
{
        struct worker_pool *pool = from_timer(pool, t, mayday_timer);
        struct work_struct *work;

        spin_lock_irq(&pool->lock);
        spin_lock(&wq_mayday_lock);             /* for wq->maydays */

        if (need_to_create_worker(pool)) {
                /*
                 * We've been trying to create a new worker but
                 * haven't been successful.  We might be hitting an
                 * allocation deadlock.  Send distress signals to
                 * rescuers.
                 */
                list_for_each_entry(work, &pool->worklist, entry)
                        send_mayday(work);
        }

        spin_unlock(&wq_mayday_lock);
        spin_unlock_irq(&pool->lock);

        mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INTERVAL);
}

/**
 * maybe_create_worker - create a new worker if necessary
 * @pool: pool to create a new worker for
 *
 * Create a new worker for @pool if necessary.  @pool is guaranteed to
 * have at least one idle worker on return from this function.  If
 * creating a new worker takes longer than MAYDAY_INTERVAL, mayday is
 * sent to all rescuers with works scheduled on @pool to resolve
 * possible allocation deadlock.
 *
 * On return, need_to_create_worker() is guaranteed to be %false and
 * may_start_working() %true.
 *
 * LOCKING:
 * spin_lock_irq(pool->lock) which may be released and regrabbed
 * multiple times.  Does GFP_KERNEL allocations.  Called only from
 * manager.
 */
static void maybe_create_worker(struct worker_pool *pool)
__releases(&pool->lock)
__acquires(&pool->lock)
{
restart:
        spin_unlock_irq(&pool->lock);

        /* if we don't make progress in MAYDAY_INITIAL_TIMEOUT, call for help */
        mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INITIAL_TIMEOUT);

        while (true) {
                if (create_worker(pool) || !need_to_create_worker(pool))
                        break;

                schedule_timeout_interruptible(CREATE_COOLDOWN);

                if (!need_to_create_worker(pool))
                        break;
        }

        del_timer_sync(&pool->mayday_timer);
        spin_lock_irq(&pool->lock);
        /*
         * This is necessary even after a new worker was just successfully
         * created as @pool->lock was dropped and the new worker might have
         * already become busy.
         */
        if (need_to_create_worker(pool))
                goto restart;
}

/**
 * manage_workers - manage worker pool
 * @worker: self
 *
 * Assume the manager role and manage the worker pool @worker belongs
 * to.  At any given time, there can be only zero or one manager per
 * pool.  The exclusion is handled automatically by this function.
 *
 * The caller can safely start processing works on false return.  On
 * true return, it's guaranteed that need_to_create_worker() is false
 * and may_start_working() is true.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock) which may be released and regrabbed
 * multiple times.  Does GFP_KERNEL allocations.
 *
 * Return:
 * %false if the pool doesn't need management and the caller can safely
 * start processing works, %true if management function was performed and
 * the conditions that the caller verified before calling the function may
 * no longer be true.
 */
static bool manage_workers(struct worker *worker)
{
        struct worker_pool *pool = worker->pool;

        if (pool->flags & POOL_MANAGER_ACTIVE)
                return false;

        pool->flags |= POOL_MANAGER_ACTIVE;
        pool->manager = worker;

        maybe_create_worker(pool);

        pool->manager = NULL;
        pool->flags &= ~POOL_MANAGER_ACTIVE;
        wake_up(&wq_manager_wait);
        return true;
}

/**
 * process_one_work - process single work
 * @worker: self
 * @work: work to process
 *
 * Process @work.  This function contains all the logics necessary to
 * process a single work including synchronization against and
 * interaction with other workers on the same cpu, queueing and
 * flushing.  As long as context requirement is met, any worker can
 * call this function to process a work.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock) which is released and regrabbed.
 */
static void process_one_work(struct worker *worker, struct work_struct *work)
__releases(&pool->lock)
__acquires(&pool->lock)
{
        struct pool_workqueue *pwq = get_work_pwq(work);
        struct worker_pool *pool = worker->pool;
        bool cpu_intensive = pwq->wq->flags & WQ_CPU_INTENSIVE;
        int work_color;
        struct worker *collision;
#ifdef CONFIG_LOCKDEP
        /*
         * It is permissible to free the struct work_struct from
         * inside the function that is called from it, this we need to
         * take into account for lockdep too.  To avoid bogus "held
         * lock freed" warnings as well as problems when looking into
         * work->lockdep_map, make a copy and use that here.
         */
        struct lockdep_map lockdep_map;

        lockdep_copy_map(&lockdep_map, &work->lockdep_map);
#endif
        /* ensure we're on the correct CPU */
        WARN_ON_ONCE(!(pool->flags & POOL_DISASSOCIATED) &&
                     raw_smp_processor_id() != pool->cpu);

        /*
         * A single work shouldn't be executed concurrently by
         * multiple workers on a single cpu.  Check whether anyone is
         * already processing the work.  If so, defer the work to the
         * currently executing one.
         */
        collision = find_worker_executing_work(pool, work);
        if (unlikely(collision)) {
                move_linked_works(work, &collision->scheduled, NULL);
                return;
        }

        /* claim and dequeue */
        debug_work_deactivate(work);
        hash_add(pool->busy_hash, &worker->hentry, (unsigned long)work);
        worker->current_work = work;
        worker->current_func = work->func;
        worker->current_pwq = pwq;
        work_color = get_work_color(work);

        /*
         * Record wq name for cmdline and debug reporting, may get
         * overridden through set_worker_desc().
         */
        strscpy(worker->desc, pwq->wq->name, WORKER_DESC_LEN);

        list_del_init(&work->entry);

        /*
         * CPU intensive works don't participate in concurrency management.
         * They're the scheduler's responsibility.  This takes @worker out
         * of concurrency management and the next code block will chain
         * execution of the pending work items.
         */
        if (unlikely(cpu_intensive))
                worker_set_flags(worker, WORKER_CPU_INTENSIVE);

        /*
         * Wake up another worker if necessary.  The condition is always
         * false for normal per-cpu workers since nr_running would always
         * be >= 1 at this point.  This is used to chain execution of the
         * pending work items for WORKER_NOT_RUNNING workers such as the
         * UNBOUND and CPU_INTENSIVE ones.
         */
        if (need_more_worker(pool))
                wake_up_worker(pool);

        /*
         * Record the last pool and clear PENDING which should be the last
         * update to @work.  Also, do this inside @pool->lock so that
         * PENDING and queued state changes happen together while IRQ is
         * disabled.
         */
        set_work_pool_and_clear_pending(work, pool->id);

        spin_unlock_irq(&pool->lock);

        lock_map_acquire(&pwq->wq->lockdep_map);
        lock_map_acquire(&lockdep_map);
        /*
         * Strictly speaking we should mark the invariant state without holding
         * any locks, that is, before these two lock_map_acquire()'s.
         *
         * However, that would result in:
         *
         *   A(W1)
         *   WFC(C)
         *              A(W1)
         *              C(C)
         *
         * Which would create W1->C->W1 dependencies, even though there is no
         * actual deadlock possible. There are two solutions, using a
         * read-recursive acquire on the work(queue) 'locks', but this will then
         * hit the lockdep limitation on recursive locks, or simply discard
         * these locks.
         *
         * AFAICT there is no possible deadlock scenario between the
         * flush_work() and complete() primitives (except for single-threaded
         * workqueues), so hiding them isn't a problem.
         */
        lockdep_invariant_state(true);
        trace_workqueue_execute_start(work);
        worker->current_func(work);
        /*
         * While we must be careful to not use "work" after this, the trace
         * point will only record its address.
         */
        trace_workqueue_execute_end(work);
        lock_map_release(&lockdep_map);
        lock_map_release(&pwq->wq->lockdep_map);

        if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
                pr_err("BUG: workqueue leaked lock or atomic: %s/0x%08x/%d\n"
                       "     last function: %ps\n",
                       current->comm, preempt_count(), task_pid_nr(current),
                       worker->current_func);
                debug_show_held_locks(current);
                dump_stack();
        }

        /*
         * The following prevents a kworker from hogging CPU on !PREEMPT
         * kernels, where a requeueing work item waiting for something to
         * happen could deadlock with stop_machine as such work item could
         * indefinitely requeue itself while all other CPUs are trapped in
         * stop_machine. At the same time, report a quiescent RCU state so
         * the same condition doesn't freeze RCU.
         */
        cond_resched();

        spin_lock_irq(&pool->lock);

        /* clear cpu intensive status */
        if (unlikely(cpu_intensive))
                worker_clr_flags(worker, WORKER_CPU_INTENSIVE);

        /* tag the worker for identification in schedule() */
        worker->last_func = worker->current_func;

        /* we're done with it, release */
        hash_del(&worker->hentry);
        worker->current_work = NULL;
        worker->current_func = NULL;
        worker->current_pwq = NULL;
        pwq_dec_nr_in_flight(pwq, work_color);
}

/**
 * process_scheduled_works - process scheduled works
 * @worker: self
 *
 * Process all scheduled works.  Please note that the scheduled list
 * may change while processing a work, so this function repeatedly
 * fetches a work from the top and executes it.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock) which may be released and regrabbed
 * multiple times.
 */
static void process_scheduled_works(struct worker *worker)
{
        while (!list_empty(&worker->scheduled)) {
                struct work_struct *work = list_first_entry(&worker->scheduled,
                                                struct work_struct, entry);
                process_one_work(worker, work);
        }
}

static void set_pf_worker(bool val)
{
        mutex_lock(&wq_pool_attach_mutex);
        if (val)
                current->flags |= PF_WQ_WORKER;
        else
                current->flags &= ~PF_WQ_WORKER;
        mutex_unlock(&wq_pool_attach_mutex);
}

/**
 * worker_thread - the worker thread function
 * @__worker: self
 *
 * The worker thread function.  All workers belong to a worker_pool -
 * either a per-cpu one or dynamic unbound one.  These workers process all
 * work items regardless of their specific target workqueue.  The only
 * exception is work items which belong to workqueues with a rescuer which
 * will be explained in rescuer_thread().
 *
 * Return: 0
 */
static int worker_thread(void *__worker)
{
        struct worker *worker = __worker;
        struct worker_pool *pool = worker->pool;

        /* tell the scheduler that this is a workqueue worker */
        set_pf_worker(true);
woke_up:
        spin_lock_irq(&pool->lock);

        /* am I supposed to die? */
        if (unlikely(worker->flags & WORKER_DIE)) {
                spin_unlock_irq(&pool->lock);
                WARN_ON_ONCE(!list_empty(&worker->entry));
                set_pf_worker(false);

                set_task_comm(worker->task, "kworker/dying");
                ida_simple_remove(&pool->worker_ida, worker->id);
                worker_detach_from_pool(worker);
                kfree(worker);
                return 0;
        }

        worker_leave_idle(worker);
recheck:
        /* no more worker necessary? */
        if (!need_more_worker(pool))
                goto sleep;

        /* do we need to manage? */
        if (unlikely(!may_start_working(pool)) && manage_workers(worker))
                goto recheck;

        /*
         * ->scheduled list can only be filled while a worker is
         * preparing to process a work or actually processing it.
         * Make sure nobody diddled with it while I was sleeping.
         */
        WARN_ON_ONCE(!list_empty(&worker->scheduled));

        /*
         * Finish PREP stage.  We're guaranteed to have at least one idle
         * worker or that someone else has already assumed the manager
         * role.  This is where @worker starts participating in concurrency
         * management if applicable and concurrency management is restored
         * after being rebound.  See rebind_workers() for details.
         */
        worker_clr_flags(worker, WORKER_PREP | WORKER_REBOUND);

        do {
                struct work_struct *work =
                        list_first_entry(&pool->worklist,
                                         struct work_struct, entry);

                pool->watchdog_ts = jiffies;

                if (likely(!(*work_data_bits(work) & WORK_STRUCT_LINKED))) {
                        /* optimization path, not strictly necessary */
                        process_one_work(worker, work);
                        if (unlikely(!list_empty(&worker->scheduled)))
                                process_scheduled_works(worker);
                } else {
                        move_linked_works(work, &worker->scheduled, NULL);
                        process_scheduled_works(worker);
                }
        } while (keep_working(pool));

        worker_set_flags(worker, WORKER_PREP);
sleep:
        /*
         * pool->lock is held and there's no work to process and no need to
         * manage, sleep.  Workers are woken up only while holding
         * pool->lock or from local cpu, so setting the current state
         * before releasing pool->lock is enough to prevent losing any
         * event.
         */
        worker_enter_idle(worker);
        __set_current_state(TASK_IDLE);
        spin_unlock_irq(&pool->lock);
        schedule();
        goto woke_up;
}

/**
 * rescuer_thread - the rescuer thread function
 * @__rescuer: self
 *
 * Workqueue rescuer thread function.  There's one rescuer for each
 * workqueue which has WQ_MEM_RECLAIM set.
 *
 * Regular work processing on a pool may block trying to create a new
 * worker which uses GFP_KERNEL allocation which has slight chance of
 * developing into deadlock if some works currently on the same queue
 * need to be processed to satisfy the GFP_KERNEL allocation.  This is
 * the problem rescuer solves.
 *
 * When such condition is possible, the pool summons rescuers of all
 * workqueues which have works queued on the pool and let them process
 * those works so that forward progress can be guaranteed.
 *
 * This should happen rarely.
 *
 * Return: 0
 */
static int rescuer_thread(void *__rescuer)
{
        struct worker *rescuer = __rescuer;
        struct workqueue_struct *wq = rescuer->rescue_wq;
        struct list_head *scheduled = &rescuer->scheduled;
        bool should_stop;

        set_user_nice(current, RESCUER_NICE_LEVEL);

        /*
         * Mark rescuer as worker too.  As WORKER_PREP is never cleared, it
         * doesn't participate in concurrency management.
         */
        set_pf_worker(true);
repeat:
        set_current_state(TASK_IDLE);

        /*
         * By the time the rescuer is requested to stop, the workqueue
         * shouldn't have any work pending, but @wq->maydays may still have
         * pwq(s) queued.  This can happen by non-rescuer workers consuming
         * all the work items before the rescuer got to them.  Go through
         * @wq->maydays processing before acting on should_stop so that the
         * list is always empty on exit.
         */
        should_stop = kthread_should_stop();

        /* see whether any pwq is asking for help */
        spin_lock_irq(&wq_mayday_lock);

        while (!list_empty(&wq->maydays)) {
                struct pool_workqueue *pwq = list_first_entry(&wq->maydays,
                                        struct pool_workqueue, mayday_node);
                struct worker_pool *pool = pwq->pool;
                struct work_struct *work, *n;
                bool first = true;

                __set_current_state(TASK_RUNNING);
                list_del_init(&pwq->mayday_node);

                spin_unlock_irq(&wq_mayday_lock);

                worker_attach_to_pool(rescuer, pool);

                spin_lock_irq(&pool->lock);

                /*
                 * Slurp in all works issued via this workqueue and
                 * process'em.
                 */
                WARN_ON_ONCE(!list_empty(scheduled));
                list_for_each_entry_safe(work, n, &pool->worklist, entry) {
                        if (get_work_pwq(work) == pwq) {
                                if (first)
                                        pool->watchdog_ts = jiffies;
                                move_linked_works(work, scheduled, &n);
                        }
                        first = false;
                }

                if (!list_empty(scheduled)) {
                        process_scheduled_works(rescuer);

                        /*
                         * The above execution of rescued work items could
                         * have created more to rescue through
                         * pwq_activate_first_delayed() or chained
                         * queueing.  Let's put @pwq back on mayday list so
                         * that such back-to-back work items, which may be
                         * being used to relieve memory pressure, don't
                         * incur MAYDAY_INTERVAL delay inbetween.
                         */
                        if (need_to_create_worker(pool)) {
                                spin_lock(&wq_mayday_lock);
                                get_pwq(pwq);
                                list_move_tail(&pwq->mayday_node, &wq->maydays);
                                spin_unlock(&wq_mayday_lock);
                        }
                }

                /*
                 * Put the reference grabbed by send_mayday().  @pool won't
                 * go away while we're still attached to it.
                 */
                put_pwq(pwq);

                /*
                 * Leave this pool.  If need_more_worker() is %true, notify a
                 * regular worker; otherwise, we end up with 0 concurrency
                 * and stalling the execution.
                 */
                if (need_more_worker(pool))
                        wake_up_worker(pool);

                spin_unlock_irq(&pool->lock);

                worker_detach_from_pool(rescuer);

                spin_lock_irq(&wq_mayday_lock);
        }

        spin_unlock_irq(&wq_mayday_lock);

        if (should_stop) {
                __set_current_state(TASK_RUNNING);
                set_pf_worker(false);
                return 0;
        }

        /* rescuers should never participate in concurrency management */
        WARN_ON_ONCE(!(rescuer->flags & WORKER_NOT_RUNNING));
        schedule();
        goto repeat;
}

/**
 * check_flush_dependency - check for flush dependency sanity
 * @target_wq: workqueue being flushed
 * @target_work: work item being flushed (NULL for workqueue flushes)
 *
 * %current is trying to flush the whole @target_wq or @target_work on it.
 * If @target_wq doesn't have %WQ_MEM_RECLAIM, verify that %current is not
 * reclaiming memory or running on a workqueue which doesn't have
 * %WQ_MEM_RECLAIM as that can break forward-progress guarantee leading to
 * a deadlock.
 */
static void check_flush_dependency(struct workqueue_struct *target_wq,
                                   struct work_struct *target_work)
{
        work_func_t target_func = target_work ? target_work->func : NULL;
        struct worker *worker;

        if (target_wq->flags & WQ_MEM_RECLAIM)
                return;

        worker = current_wq_worker();

        WARN_ONCE(current->flags & PF_MEMALLOC,
                  "workqueue: PF_MEMALLOC task %d(%s) is flushing !WQ_MEM_RECLAIM %s:%ps",
                  current->pid, current->comm, target_wq->name, target_func);
        WARN_ONCE(worker && ((worker->current_pwq->wq->flags &
                              (WQ_MEM_RECLAIM | __WQ_LEGACY)) == WQ_MEM_RECLAIM),
                  "workqueue: WQ_MEM_RECLAIM %s:%ps is flushing !WQ_MEM_RECLAIM %s:%ps",
                  worker->current_pwq->wq->name, worker->current_func,
                  target_wq->name, target_func);
}

struct wq_barrier {
        struct work_struct      work;
        struct completion       done;
        struct task_struct      *task;  /* purely informational */
};

static void wq_barrier_func(struct work_struct *work)
{
        struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
        complete(&barr->done);
}

/**
 * insert_wq_barrier - insert a barrier work
 * @pwq: pwq to insert barrier into
 * @barr: wq_barrier to insert
 * @target: target work to attach @barr to
 * @worker: worker currently executing @target, NULL if @target is not executing
 *
 * @barr is linked to @target such that @barr is completed only after
 * @target finishes execution.  Please note that the ordering
 * guarantee is observed only with respect to @target and on the local
 * cpu.
 *
 * Currently, a queued barrier can't be canceled.  This is because
 * try_to_grab_pending() can't determine whether the work to be
 * grabbed is at the head of the queue and thus can't clear LINKED
 * flag of the previous work while there must be a valid next work
 * after a work with LINKED flag set.
 *
 * Note that when @worker is non-NULL, @target may be modified
 * underneath us, so we can't reliably determine pwq from @target.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock).
 */
static void insert_wq_barrier(struct pool_workqueue *pwq,
                              struct wq_barrier *barr,
                              struct work_struct *target, struct worker *worker)
{
        struct list_head *head;
        unsigned int linked = 0;

        /*
         * debugobject calls are safe here even with pool->lock locked
         * as we know for sure that this will not trigger any of the
         * checks and call back into the fixup functions where we
         * might deadlock.
         */
        INIT_WORK_ONSTACK(&barr->work, wq_barrier_func);
        __set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work));

        init_completion_map(&barr->done, &target->lockdep_map);

        barr->task = current;

        /*
         * If @target is currently being executed, schedule the
         * barrier to the worker; otherwise, put it after @target.
         */
        if (worker)
                head = worker->scheduled.next;
        else {
                unsigned long *bits = work_data_bits(target);

                head = target->entry.next;
                /* there can already be other linked works, inherit and set */
                linked = *bits & WORK_STRUCT_LINKED;
                __set_bit(WORK_STRUCT_LINKED_BIT, bits);
        }

        debug_work_activate(&barr->work);
        insert_work(pwq, &barr->work, head,
                    work_color_to_flags(WORK_NO_COLOR) | linked);
}

/**
 * flush_workqueue_prep_pwqs - prepare pwqs for workqueue flushing
 * @wq: workqueue being flushed
 * @flush_color: new flush color, < 0 for no-op
 * @work_color: new work color, < 0 for no-op
 *
 * Prepare pwqs for workqueue flushing.
 *
 * If @flush_color is non-negative, flush_color on all pwqs should be
 * -1.  If no pwq has in-flight commands at the specified color, all
 * pwq->flush_color's stay at -1 and %false is returned.  If any pwq
 * has in flight commands, its pwq->flush_color is set to
 * @flush_color, @wq->nr_pwqs_to_flush is updated accordingly, pwq
 * wakeup logic is armed and %true is returned.
 *
 * The caller should have initialized @wq->first_flusher prior to
 * calling this function with non-negative @flush_color.  If
 * @flush_color is negative, no flush color update is done and %false
 * is returned.
 *
 * If @work_color is non-negative, all pwqs should have the same
 * work_color which is previous to @work_color and all will be
 * advanced to @work_color.
 *
 * CONTEXT:
 * mutex_lock(wq->mutex).
 *
 * Return:
 * %true if @flush_color >= 0 and there's something to flush.  %false
 * otherwise.
 */
static bool flush_workqueue_prep_pwqs(struct workqueue_struct *wq,
                                      int flush_color, int work_color)
{
        bool wait = false;
        struct pool_workqueue *pwq;

        if (flush_color >= 0) {
                WARN_ON_ONCE(atomic_read(&wq->nr_pwqs_to_flush));
                atomic_set(&wq->nr_pwqs_to_flush, 1);
        }

        for_each_pwq(pwq, wq) {
                struct worker_pool *pool = pwq->pool;

                spin_lock_irq(&pool->lock);

                if (flush_color >= 0) {
                        WARN_ON_ONCE(pwq->flush_color != -1);

                        if (pwq->nr_in_flight[flush_color]) {
                                pwq->flush_color = flush_color;
                                atomic_inc(&wq->nr_pwqs_to_flush);
                                wait = true;
                        }
                }

                if (work_color >= 0) {
                        WARN_ON_ONCE(work_color != work_next_color(pwq->work_color));
                        pwq->work_color = work_color;
                }

                spin_unlock_irq(&pool->lock);
        }

        if (flush_color >= 0 && atomic_dec_and_test(&wq->nr_pwqs_to_flush))
                complete(&wq->first_flusher->done);

        return wait;
}

/**
 * flush_workqueue - ensure that any scheduled work has run to completion.
 * @wq: workqueue to flush
 *
 * This function sleeps until all work items which were queued on entry
 * have finished execution, but it is not livelocked by new incoming ones.
 */
void flush_workqueue(struct workqueue_struct *wq)
{
        struct wq_flusher this_flusher = {
                .list = LIST_HEAD_INIT(this_flusher.list),
                .flush_color = -1,
                .done = COMPLETION_INITIALIZER_ONSTACK_MAP(this_flusher.done, wq->lockdep_map),
        };
        int next_color;

        if (WARN_ON(!wq_online))
                return;

        lock_map_acquire(&wq->lockdep_map);
        lock_map_release(&wq->lockdep_map);

        mutex_lock(&wq->mutex);

        /*
         * Start-to-wait phase
         */
        next_color = work_next_color(wq->work_color);

        if (next_color != wq->flush_color) {
                /*
                 * Color space is not full.  The current work_color
                 * becomes our flush_color and work_color is advanced
                 * by one.
                 */
                WARN_ON_ONCE(!list_empty(&wq->flusher_overflow));
                this_flusher.flush_color = wq->work_color;
                wq->work_color = next_color;

                if (!wq->first_flusher) {
                        /* no flush in progress, become the first flusher */
                        WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);

                        wq->first_flusher = &this_flusher;

                        if (!flush_workqueue_prep_pwqs(wq, wq->flush_color,
                                                       wq->work_color)) {
                                /* nothing to flush, done */
                                wq->flush_color = next_color;
                                wq->first_flusher = NULL;
                                goto out_unlock;
                        }
                } else {
                        /* wait in queue */
                        WARN_ON_ONCE(wq->flush_color == this_flusher.flush_color);
                        list_add_tail(&this_flusher.list, &wq->flusher_queue);
                        flush_workqueue_prep_pwqs(wq, -1, wq->work_color);
                }
        } else {
                /*
                 * Oops, color space is full, wait on overflow queue.
                 * The next flush completion will assign us
                 * flush_color and transfer to flusher_queue.
                 */
                list_add_tail(&this_flusher.list, &wq->flusher_overflow);
        }

        check_flush_dependency(wq, NULL);

        mutex_unlock(&wq->mutex);

        wait_for_completion(&this_flusher.done);

        /*
         * Wake-up-and-cascade phase
         *
         * First flushers are responsible for cascading flushes and
         * handling overflow.  Non-first flushers can simply return.
         */
        if (wq->first_flusher != &this_flusher)
                return;

        mutex_lock(&wq->mutex);

        /* we might have raced, check again with mutex held */
        if (wq->first_flusher != &this_flusher)
                goto out_unlock;

        wq->first_flusher = NULL;

        WARN_ON_ONCE(!list_empty(&this_flusher.list));
        WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);

        while (true) {
                struct wq_flusher *next, *tmp;

                /* complete all the flushers sharing the current flush color */
                list_for_each_entry_safe(next, tmp, &wq->flusher_queue, list) {
                        if (next->flush_color != wq->flush_color)
                                break;
                        list_del_init(&next->list);
                        complete(&next->done);
                }

                WARN_ON_ONCE(!list_empty(&wq->flusher_overflow) &&
                             wq->flush_color != work_next_color(wq->work_color));

                /* this flush_color is finished, advance by one */
                wq->flush_color = work_next_color(wq->flush_color);

                /* one color has been freed, handle overflow queue */
                if (!list_empty(&wq->flusher_overflow)) {
                        /*
                         * Assign the same color to all overflowed
                         * flushers, advance work_color and append to
                         * flusher_queue.  This is the start-to-wait
                         * phase for these overflowed flushers.
                         */
                        list_for_each_entry(tmp, &wq->flusher_overflow, list)
                                tmp->flush_color = wq->work_color;

                        wq->work_color = work_next_color(wq->work_color);

                        list_splice_tail_init(&wq->flusher_overflow,
                                              &wq->flusher_queue);
                        flush_workqueue_prep_pwqs(wq, -1, wq->work_color);
                }

                if (list_empty(&wq->flusher_queue)) {
                        WARN_ON_ONCE(wq->flush_color != wq->work_color);
                        break;
                }

                /*
                 * Need to flush more colors.  Make the next flusher
                 * the new first flusher and arm pwqs.
                 */
                WARN_ON_ONCE(wq->flush_color == wq->work_color);
                WARN_ON_ONCE(wq->flush_color != next->flush_color);

                list_del_init(&next->list);
                wq->first_flusher = next;

                if (flush_workqueue_prep_pwqs(wq, wq->flush_color, -1))
                        break;

                /*
                 * Meh... this color is already done, clear first
                 * flusher and repeat cascading.
                 */
                wq->first_flusher = NULL;
        }

out_unlock:
        mutex_unlock(&wq->mutex);
}
EXPORT_SYMBOL(flush_workqueue);

/**
 * drain_workqueue - drain a workqueue
 * @wq: workqueue to drain
 *
 * Wait until the workqueue becomes empty.  While draining is in progress,
 * only chain queueing is allowed.  IOW, only currently pending or running
 * work items on @wq can queue further work items on it.  @wq is flushed
 * repeatedly until it becomes empty.  The number of flushing is determined
 * by the depth of chaining and should be relatively short.  Whine if it
 * takes too long.
 */
void drain_workqueue(struct workqueue_struct *wq)
{
        unsigned int flush_cnt = 0;
        struct pool_workqueue *pwq;

        /*
         * __queue_work() needs to test whether there are drainers, is much
         * hotter than drain_workqueue() and already looks at @wq->flags.
         * Use __WQ_DRAINING so that queue doesn't have to check nr_drainers.
         */
        mutex_lock(&wq->mutex);
        if (!wq->nr_drainers++)
                wq->flags |= __WQ_DRAINING;
        mutex_unlock(&wq->mutex);
reflush:
        flush_workqueue(wq);

        mutex_lock(&wq->mutex);

        for_each_pwq(pwq, wq) {
                bool drained;

                spin_lock_irq(&pwq->pool->lock);
                drained = !pwq->nr_active && list_empty(&pwq->delayed_works);
                spin_unlock_irq(&pwq->pool->lock);

                if (drained)
                        continue;

                if (++flush_cnt == 10 ||
                    (flush_cnt % 100 == 0 && flush_cnt <= 1000))
                        pr_warn("workqueue %s: drain_workqueue() isn't complete after %u tries\n",
                                wq->name, flush_cnt);

                mutex_unlock(&wq->mutex);
                goto reflush;
        }

        if (!--wq->nr_drainers)
                wq->flags &= ~__WQ_DRAINING;
        mutex_unlock(&wq->mutex);
}
EXPORT_SYMBOL_GPL(drain_workqueue);

static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
                             bool from_cancel)
{
        struct worker *worker = NULL;
        struct worker_pool *pool;
        struct pool_workqueue *pwq;

        might_sleep();

        rcu_read_lock();
        pool = get_work_pool(work);
        if (!pool) {
                rcu_read_unlock();
                return false;
        }

        spin_lock_irq(&pool->lock);
        /* see the comment in try_to_grab_pending() with the same code */
        pwq = get_work_pwq(work);
        if (pwq) {
                if (unlikely(pwq->pool != pool))
                        goto already_gone;
        } else {
                worker = find_worker_executing_work(pool, work);
                if (!worker)
                        goto already_gone;
                pwq = worker->current_pwq;
        }

        check_flush_dependency(pwq->wq, work);

        insert_wq_barrier(pwq, barr, work, worker);
        spin_unlock_irq(&pool->lock);

        /*
         * Force a lock recursion deadlock when using flush_work() inside a
         * single-threaded or rescuer equipped workqueue.
         *
         * For single threaded workqueues the deadlock happens when the work
         * is after the work issuing the flush_work(). For rescuer equipped
         * workqueues the deadlock happens when the rescuer stalls, blocking
         * forward progress.
         */
        if (!from_cancel &&
            (pwq->wq->saved_max_active == 1 || pwq->wq->rescuer)) {
                lock_map_acquire(&pwq->wq->lockdep_map);
                lock_map_release(&pwq->wq->lockdep_map);
        }
        rcu_read_unlock();
        return true;
already_gone:
        spin_unlock_irq(&pool->lock);
        rcu_read_unlock();
        return false;
}

static bool __flush_work(struct work_struct *work, bool from_cancel)
{
        struct wq_barrier barr;

        if (WARN_ON(!wq_online))
                return false;

        if (WARN_ON(!work->func))
                return false;

        if (!from_cancel) {
                lock_map_acquire(&work->lockdep_map);
                lock_map_release(&work->lockdep_map);
        }

        if (start_flush_work(work, &barr, from_cancel)) {
                wait_for_completion(&barr.done);
                destroy_work_on_stack(&barr.work);
                return true;
        } else {
                return false;
        }
}

/**
 * flush_work - wait for a work to finish executing the last queueing instance
 * @work: the work to flush
 *
 * Wait until @work has finished execution.  @work is guaranteed to be idle
 * on return if it hasn't been requeued since flush started.
 *
 * Return:
 * %true if flush_work() waited for the work to finish execution,
 * %false if it was already idle.
 */
bool flush_work(struct work_struct *work)
{
        return __flush_work(work, false);
}
EXPORT_SYMBOL_GPL(flush_work);

struct cwt_wait {
        wait_queue_entry_t              wait;
        struct work_struct      *work;
};

static int cwt_wakefn(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
{
        struct cwt_wait *cwait = container_of(wait, struct cwt_wait, wait);

        if (cwait->work != key)
                return 0;
        return autoremove_wake_function(wait, mode, sync, key);
}

static bool __cancel_work_timer(struct work_struct *work, bool is_dwork)
{
        static DECLARE_WAIT_QUEUE_HEAD(cancel_waitq);
        unsigned long flags;
        int ret;

        do {
                ret = try_to_grab_pending(work, is_dwork, &flags);
                /*
                 * If someone else is already canceling, wait for it to
                 * finish.  flush_work() doesn't work for PREEMPT_NONE
                 * because we may get scheduled between @work's completion
                 * and the other canceling task resuming and clearing
                 * CANCELING - flush_work() will return false immediately
                 * as @work is no longer busy, try_to_grab_pending() will
                 * return -ENOENT as @work is still being canceled and the
                 * other canceling task won't be able to clear CANCELING as
                 * we're hogging the CPU.
                 *
                 * Let's wait for completion using a waitqueue.  As this
                 * may lead to the thundering herd problem, use a custom
                 * wake function which matches @work along with exclusive
                 * wait and wakeup.
                 */
                if (unlikely(ret == -ENOENT)) {
                        struct cwt_wait cwait;

                        init_wait(&cwait.wait);
                        cwait.wait.func = cwt_wakefn;
                        cwait.work = work;

                        prepare_to_wait_exclusive(&cancel_waitq, &cwait.wait,
                                                  TASK_UNINTERRUPTIBLE);
                        if (work_is_canceling(work))
                                schedule();
                        finish_wait(&cancel_waitq, &cwait.wait);
                }
        } while (unlikely(ret < 0));

        /* tell other tasks trying to grab @work to back off */
        mark_work_canceling(work);
        local_irq_restore(flags);

        /*
         * This allows canceling during early boot.  We know that @work
         * isn't executing.
         */
        if (wq_online)
                __flush_work(work, true);

        clear_work_data(work);

        /*
         * Paired with prepare_to_wait() above so that either
         * waitqueue_active() is visible here or !work_is_canceling() is
         * visible there.
         */
        smp_mb();
        if (waitqueue_active(&cancel_waitq))
                __wake_up(&cancel_waitq, TASK_NORMAL, 1, work);

        return ret;
}

/**
 * cancel_work_sync - cancel a work and wait for it to finish
 * @work: the work to cancel
 *
 * Cancel @work and wait for its execution to finish.  This function
 * can be used even if the work re-queues itself or migrates to
 * another workqueue.  On return from this function, @work is
 * guaranteed to be not pending or executing on any CPU.
 *
 * cancel_work_sync(&delayed_work->work) must not be used for
 * delayed_work's.  Use cancel_delayed_work_sync() instead.
 *
 * The caller must ensure that the workqueue on which @work was last
 * queued can't be destroyed before this function returns.
 *
 * Return:
 * %true if @work was pending, %false otherwise.
 */
bool cancel_work_sync(struct work_struct *work)
{
        return __cancel_work_timer(work, false);
}
EXPORT_SYMBOL_GPL(cancel_work_sync);

/**
 * flush_delayed_work - wait for a dwork to finish executing the last queueing
 * @dwork: the delayed work to flush
 *
 * Delayed timer is cancelled and the pending work is queued for
 * immediate execution.  Like flush_work(), this function only
 * considers the last queueing instance of @dwork.
 *
 * Return:
 * %true if flush_work() waited for the work to finish execution,
 * %false if it was already idle.
 */
bool flush_delayed_work(struct delayed_work *dwork)
{
        local_irq_disable();
        if (del_timer_sync(&dwork->timer))
                __queue_work(dwork->cpu, dwork->wq, &dwork->work);
        local_irq_enable();
        return flush_work(&dwork->work);
}
EXPORT_SYMBOL(flush_delayed_work);

/**
 * flush_rcu_work - wait for a rwork to finish executing the last queueing
 * @rwork: the rcu work to flush
 *
 * Return:
 * %true if flush_rcu_work() waited for the work to finish execution,
 * %false if it was already idle.
 */
bool flush_rcu_work(struct rcu_work *rwork)
{
        if (test_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&rwork->work))) {
                rcu_barrier();
                flush_work(&rwork->work);
                return true;
        } else {
                return flush_work(&rwork->work);
        }
}
EXPORT_SYMBOL(flush_rcu_work);

static bool __cancel_work(struct work_struct *work, bool is_dwork)
{
        unsigned long flags;
        int ret;

        do {
                ret = try_to_grab_pending(work, is_dwork, &flags);
        } while (unlikely(ret == -EAGAIN));

        if (unlikely(ret < 0))
                return false;

        set_work_pool_and_clear_pending(work, get_work_pool_id(work));
        local_irq_restore(flags);
        return ret;
}

/**
 * cancel_delayed_work - cancel a delayed work
 * @dwork: delayed_work to cancel
 *
 * Kill off a pending delayed_work.
 *
 * Return: %true if @dwork was pending and canceled; %false if it wasn't
 * pending.
 *
 * Note:
 * The work callback function may still be running on return, unless
 * it returns %true and the work doesn't re-arm itself.  Explicitly flush or
 * use cancel_delayed_work_sync() to wait on it.
 *
 * This function is safe to call from any context including IRQ handler.
 */
bool cancel_delayed_work(struct delayed_work *dwork)
{
        return __cancel_work(&dwork->work, true);
}
EXPORT_SYMBOL(cancel_delayed_work);

/**
 * cancel_delayed_work_sync - cancel a delayed work and wait for it to finish
 * @dwork: the delayed work cancel
 *
 * This is cancel_work_sync() for delayed works.
 *
 * Return:
 * %true if @dwork was pending, %false otherwise.
 */
bool cancel_delayed_work_sync(struct delayed_work *dwork)
{
        return __cancel_work_timer(&dwork->work, true);
}
EXPORT_SYMBOL(cancel_delayed_work_sync);

/**
 * schedule_on_each_cpu - execute a function synchronously on each online CPU
 * @func: the function to call
 *
 * schedule_on_each_cpu() executes @func on each online CPU using the
 * system workqueue and blocks until all CPUs have completed.
 * schedule_on_each_cpu() is very slow.
 *
 * Return:
 * 0 on success, -errno on failure.
 */
int schedule_on_each_cpu(work_func_t func)
{
        int cpu;
        struct work_struct __percpu *works;

        works = alloc_percpu(struct work_struct);
        if (!works)
                return -ENOMEM;

        get_online_cpus();

        for_each_online_cpu(cpu) {
                struct work_struct *work = per_cpu_ptr(works, cpu);

                INIT_WORK(work, func);
                schedule_work_on(cpu, work);
        }

        for_each_online_cpu(cpu)
                flush_work(per_cpu_ptr(works, cpu));

        put_online_cpus();
        free_percpu(works);
        return 0;
}

/**
 * execute_in_process_context - reliably execute the routine with user context
 * @fn:         the function to execute
 * @ew:         guaranteed storage for the execute work structure (must
 *              be available when the work executes)
 *
 * Executes the function immediately if process context is available,
 * otherwise schedules the function for delayed execution.
 *
 * Return:      0 - function was executed
 *              1 - function was scheduled for execution
 */
int execute_in_process_context(work_func_t fn, struct execute_work *ew)
{
        if (!in_interrupt()) {
                fn(&ew->work);
                return 0;
        }

        INIT_WORK(&ew->work, fn);
        schedule_work(&ew->work);

        return 1;
}
EXPORT_SYMBOL_GPL(execute_in_process_context);

/**
 * free_workqueue_attrs - free a workqueue_attrs
 * @attrs: workqueue_attrs to free
 *
 * Undo alloc_workqueue_attrs().
 */
void free_workqueue_attrs(struct workqueue_attrs *attrs)
{
        if (attrs) {
                free_cpumask_var(attrs->cpumask);
                kfree(attrs);
        }
}

/**
 * alloc_workqueue_attrs - allocate a workqueue_attrs
 *
 * Allocate a new workqueue_attrs, initialize with default settings and
 * return it.
 *
 * Return: The allocated new workqueue_attr on success. %NULL on failure.
 */
struct workqueue_attrs *alloc_workqueue_attrs(void)
{
        struct workqueue_attrs *attrs;

        attrs = kzalloc(sizeof(*attrs), GFP_KERNEL);
        if (!attrs)
                goto fail;
        if (!alloc_cpumask_var(&attrs->cpumask, GFP_KERNEL))
                goto fail;

        cpumask_copy(attrs->cpumask, cpu_possible_mask);
        return attrs;
fail:
        free_workqueue_attrs(attrs);
        return NULL;
}

static void copy_workqueue_attrs(struct workqueue_attrs *to,
                                 const struct workqueue_attrs *from)
{
        to->nice = from->nice;
        cpumask_copy(to->cpumask, from->cpumask);
        /*
         * Unlike hash and equality test, this function doesn't ignore
         * ->no_numa as it is used for both pool and wq attrs.  Instead,
         * get_unbound_pool() explicitly clears ->no_numa after copying.
         */
        to->no_numa = from->no_numa;
}

/* hash value of the content of @attr */
static u32 wqattrs_hash(const struct workqueue_attrs *attrs)
{
        u32 hash = 0;

        hash = jhash_1word(attrs->nice, hash);
        hash = jhash(cpumask_bits(attrs->cpumask),
                     BITS_TO_LONGS(nr_cpumask_bits) * sizeof(long), hash);
        return hash;
}

/* content equality test */
static bool wqattrs_equal(const struct workqueue_attrs *a,
                          const struct workqueue_attrs *b)
{
        if (a->nice != b->nice)
                return false;
        if (!cpumask_equal(a->cpumask, b->cpumask))
                return false;
        return true;
}

/**
 * init_worker_pool - initialize a newly zalloc'd worker_pool
 * @pool: worker_pool to initialize
 *
 * Initialize a newly zalloc'd @pool.  It also allocates @pool->attrs.
 *
 * Return: 0 on success, -errno on failure.  Even on failure, all fields
 * inside @pool proper are initialized and put_unbound_pool() can be called
 * on @pool safely to release it.
 */
static int init_worker_pool(struct worker_pool *pool)
{
        spin_lock_init(&pool->lock);
        pool->id = -1;
        pool->cpu = -1;
        pool->node = NUMA_NO_NODE;
        pool->flags |= POOL_DISASSOCIATED;
        pool->watchdog_ts = jiffies;
        INIT_LIST_HEAD(&pool->worklist);
        INIT_LIST_HEAD(&pool->idle_list);
        hash_init(pool->busy_hash);

        timer_setup(&pool->idle_timer, idle_worker_timeout, TIMER_DEFERRABLE);

        timer_setup(&pool->mayday_timer, pool_mayday_timeout, 0);

        INIT_LIST_HEAD(&pool->workers);

        ida_init(&pool->worker_ida);
        INIT_HLIST_NODE(&pool->hash_node);
        pool->refcnt = 1;

        /* shouldn't fail above this point */
        pool->attrs = alloc_workqueue_attrs();
        if (!pool->attrs)
                return -ENOMEM;
        return 0;
}

#ifdef CONFIG_LOCKDEP
static void wq_init_lockdep(struct workqueue_struct *wq)
{
        char *lock_name;

        lockdep_register_key(&wq->key);
        lock_name = kasprintf(GFP_KERNEL, "%s%s", "(wq_completion)", wq->name);
        if (!lock_name)
                lock_name = wq->name;

        wq->lock_name = lock_name;
        lockdep_init_map(&wq->lockdep_map, lock_name, &wq->key, 0);
}

static void wq_unregister_lockdep(struct workqueue_struct *wq)
{
        lockdep_unregister_key(&wq->key);
}

static void wq_free_lockdep(struct workqueue_struct *wq)
{
        if (wq->lock_name != wq->name)
                kfree(wq->lock_name);
}
#else
static void wq_init_lockdep(struct workqueue_struct *wq)
{
}

static void wq_unregister_lockdep(struct workqueue_struct *wq)
{
}

static void wq_free_lockdep(struct workqueue_struct *wq)
{
}
#endif

static void rcu_free_wq(struct rcu_head *rcu)
{
        struct workqueue_struct *wq =
                container_of(rcu, struct workqueue_struct, rcu);

        wq_free_lockdep(wq);

        if (!(wq->flags & WQ_UNBOUND))
                free_percpu(wq->cpu_pwqs);
        else
                free_workqueue_attrs(wq->unbound_attrs);

        kfree(wq->rescuer);
        kfree(wq);
}

static void rcu_free_pool(struct rcu_head *rcu)
{
        struct worker_pool *pool = container_of(rcu, struct worker_pool, rcu);

        ida_destroy(&pool->worker_ida);
        free_workqueue_attrs(pool->attrs);
        kfree(pool);
}

/**
 * put_unbound_pool - put a worker_pool
 * @pool: worker_pool to put
 *
 * Put @pool.  If its refcnt reaches zero, it gets destroyed in RCU
 * safe manner.  get_unbound_pool() calls this function on its failure path
 * and this function should be able to release pools which went through,
 * successfully or not, init_worker_pool().
 *
 * Should be called with wq_pool_mutex held.
 */
static void put_unbound_pool(struct worker_pool *pool)
{
        DECLARE_COMPLETION_ONSTACK(detach_completion);
        struct worker *worker;

        lockdep_assert_held(&wq_pool_mutex);

        if (--pool->refcnt)
                return;

        /* sanity checks */
        if (WARN_ON(!(pool->cpu < 0)) ||
            WARN_ON(!list_empty(&pool->worklist)))
                return;

        /* release id and unhash */
        if (pool->id >= 0)
                idr_remove(&worker_pool_idr, pool->id);
        hash_del(&pool->hash_node);

        /*
         * Become the manager and destroy all workers.  This prevents
         * @pool's workers from blocking on attach_mutex.  We're the last
         * manager and @pool gets freed with the flag set.
         */
        spin_lock_irq(&pool->lock);
        wait_event_lock_irq(wq_manager_wait,
                            !(pool->flags & POOL_MANAGER_ACTIVE), pool->lock);
        pool->flags |= POOL_MANAGER_ACTIVE;

        while ((worker = first_idle_worker(pool)))
                destroy_worker(worker);
        WARN_ON(pool->nr_workers || pool->nr_idle);
        spin_unlock_irq(&pool->lock);

        mutex_lock(&wq_pool_attach_mutex);
        if (!list_empty(&pool->workers))
                pool->detach_completion = &detach_completion;
        mutex_unlock(&wq_pool_attach_mutex);

        if (pool->detach_completion)
                wait_for_completion(pool->detach_completion);

        /* shut down the timers */
        del_timer_sync(&pool->idle_timer);
        del_timer_sync(&pool->mayday_timer);

        /* RCU protected to allow dereferences from get_work_pool() */
        call_rcu(&pool->rcu, rcu_free_pool);
}

/**
 * get_unbound_pool - get a worker_pool with the specified attributes
 * @attrs: the attributes of the worker_pool to get
 *
 * Obtain a worker_pool which has the same attributes as @attrs, bump the
 * reference count and return it.  If there already is a matching
 * worker_pool, it will be used; otherwise, this function attempts to
 * create a new one.
 *
 * Should be called with wq_pool_mutex held.
 *
 * Return: On success, a worker_pool with the same attributes as @attrs.
 * On failure, %NULL.
 */
static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
{
        u32 hash = wqattrs_hash(attrs);
        struct worker_pool *pool;
        int node;
        int target_node = NUMA_NO_NODE;

        lockdep_assert_held(&wq_pool_mutex);

        /* do we already have a matching pool? */
        hash_for_each_possible(unbound_pool_hash, pool, hash_node, hash) {
                if (wqattrs_equal(pool->attrs, attrs)) {
                        pool->refcnt++;
                        return pool;
                }
        }

        /* if cpumask is contained inside a NUMA node, we belong to that node */
        if (wq_numa_enabled) {
                for_each_node(node) {
                        if (cpumask_subset(attrs->cpumask,
                                           wq_numa_possible_cpumask[node])) {
                                target_node = node;
                                break;
                        }
                }
        }

        /* nope, create a new one */
        pool = kzalloc_node(sizeof(*pool), GFP_KERNEL, target_node);
        if (!pool || init_worker_pool(pool) < 0)
                goto fail;

        lockdep_set_subclass(&pool->lock, 1);   /* see put_pwq() */
        copy_workqueue_attrs(pool->attrs, attrs);
        pool->node = target_node;

        /*
         * no_numa isn't a worker_pool attribute, always clear it.  See
         * 'struct workqueue_attrs' comments for detail.
         */
        pool->attrs->no_numa = false;

        if (worker_pool_assign_id(pool) < 0)
                goto fail;

        /* create and start the initial worker */
        if (wq_online && !create_worker(pool))
                goto fail;

        /* install */
        hash_add(unbound_pool_hash, &pool->hash_node, hash);

        return pool;
fail:
        if (pool)
                put_unbound_pool(pool);
        return NULL;
}

static void rcu_free_pwq(struct rcu_head *rcu)
{
        kmem_cache_free(pwq_cache,
                        container_of(rcu, struct pool_workqueue, rcu));
}

/*
 * Scheduled on system_wq by put_pwq() when an unbound pwq hits zero refcnt
 * and needs to be destroyed.
 */
static void pwq_unbound_release_workfn(struct work_struct *work)
{
        struct pool_workqueue *pwq = container_of(work, struct pool_workqueue,
                                                  unbound_release_work);
        struct workqueue_struct *wq = pwq->wq;
        struct worker_pool *pool = pwq->pool;
        bool is_last;

        if (WARN_ON_ONCE(!(wq->flags & WQ_UNBOUND)))
                return;

        mutex_lock(&wq->mutex);
        list_del_rcu(&pwq->pwqs_node);
        is_last = list_empty(&wq->pwqs);
        mutex_unlock(&wq->mutex);

        mutex_lock(&wq_pool_mutex);
        put_unbound_pool(pool);
        mutex_unlock(&wq_pool_mutex);

        call_rcu(&pwq->rcu, rcu_free_pwq);

        /*
         * If we're the last pwq going away, @wq is already dead and no one
         * is gonna access it anymore.  Schedule RCU free.
         */
        if (is_last) {
                wq_unregister_lockdep(wq);
                call_rcu(&wq->rcu, rcu_free_wq);
        }
}

/**
 * pwq_adjust_max_active - update a pwq's max_active to the current setting
 * @pwq: target pool_workqueue
 *
 * If @pwq isn't freezing, set @pwq->max_active to the associated
 * workqueue's saved_max_active and activate delayed work items
 * accordingly.  If @pwq is freezing, clear @pwq->max_active to zero.
 */
static void pwq_adjust_max_active(struct pool_workqueue *pwq)
{
        struct workqueue_struct *wq = pwq->wq;
        bool freezable = wq->flags & WQ_FREEZABLE;
        unsigned long flags;

        /* for @wq->saved_max_active */
        lockdep_assert_held(&wq->mutex);

        /* fast exit for non-freezable wqs */
        if (!freezable && pwq->max_active == wq->saved_max_active)
                return;

        /* this function can be called during early boot w/ irq disabled */
        spin_lock_irqsave(&pwq->pool->lock, flags);

        /*
         * During [un]freezing, the caller is responsible for ensuring that
         * this function is called at least once after @workqueue_freezing
         * is updated and visible.
         */
        if (!freezable || !workqueue_freezing) {
                pwq->max_active = wq->saved_max_active;

                while (!list_empty(&pwq->delayed_works) &&
                       pwq->nr_active < pwq->max_active)
                        pwq_activate_first_delayed(pwq);

                /*
                 * Need to kick a worker after thawed or an unbound wq's
                 * max_active is bumped.  It's a slow path.  Do it always.
                 */
                wake_up_worker(pwq->pool);
        } else {
                pwq->max_active = 0;
        }

        spin_unlock_irqrestore(&pwq->pool->lock, flags);
}

/* initialize newly alloced @pwq which is associated with @wq and @pool */
static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq,
                     struct worker_pool *pool)
{
        BUG_ON((unsigned long)pwq & WORK_STRUCT_FLAG_MASK);

        memset(pwq, 0, sizeof(*pwq));

        pwq->pool = pool;
        pwq->wq = wq;
        pwq->flush_color = -1;
        pwq->refcnt = 1;
        INIT_LIST_HEAD(&pwq->delayed_works);
        INIT_LIST_HEAD(&pwq->pwqs_node);
        INIT_LIST_HEAD(&pwq->mayday_node);
        INIT_WORK(&pwq->unbound_release_work, pwq_unbound_release_workfn);
}

/* sync @pwq with the current state of its associated wq and link it */
static void link_pwq(struct pool_workqueue *pwq)
{
        struct workqueue_struct *wq = pwq->wq;

        lockdep_assert_held(&wq->mutex);

        /* may be called multiple times, ignore if already linked */
        if (!list_empty(&pwq->pwqs_node))
                return;

        /* set the matching work_color */
        pwq->work_color = wq->work_color;

        /* sync max_active to the current setting */
        pwq_adjust_max_active(pwq);

        /* link in @pwq */
        list_add_rcu(&pwq->pwqs_node, &wq->pwqs);
}

/* obtain a pool matching @attr and create a pwq associating the pool and @wq */
static struct pool_workqueue *alloc_unbound_pwq(struct workqueue_struct *wq,
                                        const struct workqueue_attrs *attrs)
{
        struct worker_pool *pool;
        struct pool_workqueue *pwq;

        lockdep_assert_held(&wq_pool_mutex);

        pool = get_unbound_pool(attrs);
        if (!pool)
                return NULL;

        pwq = kmem_cache_alloc_node(pwq_cache, GFP_KERNEL, pool->node);
        if (!pwq) {
                put_unbound_pool(pool);
                return NULL;
        }

        init_pwq(pwq, wq, pool);
        return pwq;
}

/**
 * wq_calc_node_cpumask - calculate a wq_attrs' cpumask for the specified node
 * @attrs: the wq_attrs of the default pwq of the target workqueue
 * @node: the target NUMA node
 * @cpu_going_down: if >= 0, the CPU to consider as offline
 * @cpumask: outarg, the resulting cpumask
 *
 * Calculate the cpumask a workqueue with @attrs should use on @node.  If
 * @cpu_going_down is >= 0, that cpu is considered offline during
 * calculation.  The result is stored in @cpumask.
 *
 * If NUMA affinity is not enabled, @attrs->cpumask is always used.  If
 * enabled and @node has online CPUs requested by @attrs, the returned
 * cpumask is the intersection of the possible CPUs of @node and
 * @attrs->cpumask.
 *
 * The caller is responsible for ensuring that the cpumask of @node stays
 * stable.
 *
 * Return: %true if the resulting @cpumask is different from @attrs->cpumask,
 * %false if equal.
 */
static bool wq_calc_node_cpumask(const struct workqueue_attrs *attrs, int node,
                                 int cpu_going_down, cpumask_t *cpumask)
{
        if (!wq_numa_enabled || attrs->no_numa)
                goto use_dfl;

        /* does @node have any online CPUs @attrs wants? */
        cpumask_and(cpumask, cpumask_of_node(node), attrs->cpumask);
        if (cpu_going_down >= 0)
                cpumask_clear_cpu(cpu_going_down, cpumask);

        if (cpumask_empty(cpumask))
                goto use_dfl;

        /* yeap, return possible CPUs in @node that @attrs wants */
        cpumask_and(cpumask, attrs->cpumask, wq_numa_possible_cpumask[node]);

        if (cpumask_empty(cpumask)) {
                pr_warn_once("WARNING: workqueue cpumask: online intersect > "
                                "possible intersect\n");
                return false;
        }

        return !cpumask_equal(cpumask, attrs->cpumask);

use_dfl:
        cpumask_copy(cpumask, attrs->cpumask);
        return false;
}

/* install @pwq into @wq's numa_pwq_tbl[] for @node and return the old pwq */
static struct pool_workqueue *numa_pwq_tbl_install(struct workqueue_struct *wq,
                                                   int node,
                                                   struct pool_workqueue *pwq)
{
        struct pool_workqueue *old_pwq;

        lockdep_assert_held(&wq_pool_mutex);
        lockdep_assert_held(&wq->mutex);

        /* link_pwq() can handle duplicate calls */
        link_pwq(pwq);

        old_pwq = rcu_access_pointer(wq->numa_pwq_tbl[node]);
        rcu_assign_pointer(wq->numa_pwq_tbl[node], pwq);
        return old_pwq;
}

/* context to store the prepared attrs & pwqs before applying */
struct apply_wqattrs_ctx {
        struct workqueue_struct *wq;            /* target workqueue */
        struct workqueue_attrs  *attrs;         /* attrs to apply */
        struct list_head        list;           /* queued for batching commit */
        struct pool_workqueue   *dfl_pwq;
        struct pool_workqueue   *pwq_tbl[];
};

/* free the resources after success or abort */
static void apply_wqattrs_cleanup(struct apply_wqattrs_ctx *ctx)
{
        if (ctx) {
                int node;

                for_each_node(node)
                        put_pwq_unlocked(ctx->pwq_tbl[node]);
                put_pwq_unlocked(ctx->dfl_pwq);

                free_workqueue_attrs(ctx->attrs);

                kfree(ctx);
        }
}

/* allocate the attrs and pwqs for later installation */
static struct apply_wqattrs_ctx *
apply_wqattrs_prepare(struct workqueue_struct *wq,
                      const struct workqueue_attrs *attrs)
{
        struct apply_wqattrs_ctx *ctx;
        struct workqueue_attrs *new_attrs, *tmp_attrs;
        int node;

        lockdep_assert_held(&wq_pool_mutex);

        ctx = kzalloc(struct_size(ctx, pwq_tbl, nr_node_ids), GFP_KERNEL);

        new_attrs = alloc_workqueue_attrs();
        tmp_attrs = alloc_workqueue_attrs();
        if (!ctx || !new_attrs || !tmp_attrs)
                goto out_free;

        /*
         * Calculate the attrs of the default pwq.
         * If the user configured cpumask doesn't overlap with the
         * wq_unbound_cpumask, we fallback to the wq_unbound_cpumask.
         */
        copy_workqueue_attrs(new_attrs, attrs);
        cpumask_and(new_attrs->cpumask, new_attrs->cpumask, wq_unbound_cpumask);
        if (unlikely(cpumask_empty(new_attrs->cpumask)))
                cpumask_copy(new_attrs->cpumask, wq_unbound_cpumask);

        /*
         * We may create multiple pwqs with differing cpumasks.  Make a
         * copy of @new_attrs which will be modified and used to obtain
         * pools.
         */
        copy_workqueue_attrs(tmp_attrs, new_attrs);

        /*
         * If something goes wrong during CPU up/down, we'll fall back to
         * the default pwq covering whole @attrs->cpumask.  Always create
         * it even if we don't use it immediately.
         */
        ctx->dfl_pwq = alloc_unbound_pwq(wq, new_attrs);
        if (!ctx->dfl_pwq)
                goto out_free;

        for_each_node(node) {
                if (wq_calc_node_cpumask(new_attrs, node, -1, tmp_attrs->cpumask)) {
                        ctx->pwq_tbl[node] = alloc_unbound_pwq(wq, tmp_attrs);
                        if (!ctx->pwq_tbl[node])
                                goto out_free;
                } else {
                        ctx->dfl_pwq->refcnt++;
                        ctx->pwq_tbl[node] = ctx->dfl_pwq;
                }
        }

        /* save the user configured attrs and sanitize it. */
        copy_workqueue_attrs(new_attrs, attrs);
        cpumask_and(new_attrs->cpumask, new_attrs->cpumask, cpu_possible_mask);
        ctx->attrs = new_attrs;

        ctx->wq = wq;
        free_workqueue_attrs(tmp_attrs);
        return ctx;

out_free:
        free_workqueue_attrs(tmp_attrs);
        free_workqueue_attrs(new_attrs);
        apply_wqattrs_cleanup(ctx);
        return NULL;
}

/* set attrs and install prepared pwqs, @ctx points to old pwqs on return */
static void apply_wqattrs_commit(struct apply_wqattrs_ctx *ctx)
{
        int node;

        /* all pwqs have been created successfully, let's install'em */
        mutex_lock(&ctx->wq->mutex);

        copy_workqueue_attrs(ctx->wq->unbound_attrs, ctx->attrs);

        /* save the previous pwq and install the new one */
        for_each_node(node)
                ctx->pwq_tbl[node] = numa_pwq_tbl_install(ctx->wq, node,
                                                          ctx->pwq_tbl[node]);

        /* @dfl_pwq might not have been used, ensure it's linked */
        link_pwq(ctx->dfl_pwq);
        swap(ctx->wq->dfl_pwq, ctx->dfl_pwq);

        mutex_unlock(&ctx->wq->mutex);
}

static void apply_wqattrs_lock(void)
{
        /* CPUs should stay stable across pwq creations and installations */
        get_online_cpus();
        mutex_lock(&wq_pool_mutex);
}

static void apply_wqattrs_unlock(void)
{
        mutex_unlock(&wq_pool_mutex);
        put_online_cpus();
}

static int apply_workqueue_attrs_locked(struct workqueue_struct *wq,
                                        const struct workqueue_attrs *attrs)
{
        struct apply_wqattrs_ctx *ctx;

        /* only unbound workqueues can change attributes */
        if (WARN_ON(!(wq->flags & WQ_UNBOUND)))
                return -EINVAL;

        /* creating multiple pwqs breaks ordering guarantee */