workqueue.c

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/*
 * kernel/workqueue.c - generic async execution with shared worker pool
 *
 * Copyright (C) 2002       Ingo Molnar
 *
 *   Derived from the taskqueue/keventd code by:
 *     David Woodhouse <[email protected]>
 *     Andrew Morton
 *     Kai Petzke <[email protected]>
 *     Theodore Ts'o <[email protected]>
 *
 * Made to use alloc_percpu by Christoph Lameter.
 *
 * Copyright (C) 2010       SUSE Linux Products GmbH
 * Copyright (C) 2010       Tejun Heo <[email protected]>
 *
 * This is the generic async execution mechanism.  Work items as are
 * executed in process context.  The worker pool is shared and
 * automatically managed.  There is one worker pool for each CPU and
 * one extra for works which are better served by workers which are
 * not bound to any specific CPU.
 *
 * Please read Documentation/workqueue.txt 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/kallsyms.h>
#include <linux/debug_locks.h>
#include <linux/lockdep.h>
#include <linux/idr.h>

#include "workqueue_sched.h"

enum {
    /*
     * global_cwq flags
     *
     * A bound gcwq 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 gcwq behaves as an unbound one.
     *
     * Note that DISASSOCIATED can be flipped only while holding
     * assoc_mutex of all pools on the gcwq to avoid changing binding
     * state while create_worker() is in progress.
     */
    GCWQ_DISASSOCIATED  = 1 << 0,   /* cpu can't serve workers */
    GCWQ_FREEZING       = 1 << 1,   /* freeze in progress */

    /* pool flags */
    POOL_MANAGE_WORKERS = 1 << 0,   /* need to manage workers */
    POOL_MANAGING_WORKERS   = 1 << 1,       /* managing workers */

    /* worker flags */
    WORKER_STARTED      = 1 << 0,   /* started */
    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_NOT_RUNNING  = WORKER_PREP | WORKER_UNBOUND |
                  WORKER_CPU_INTENSIVE,

    NR_WORKER_POOLS     = 2,        /* # worker pools per gcwq */

    BUSY_WORKER_HASH_ORDER  = 6,        /* 64 pointers */
    BUSY_WORKER_HASH_SIZE   = 1 << BUSY_WORKER_HASH_ORDER,
    BUSY_WORKER_HASH_MASK   = BUSY_WORKER_HASH_SIZE - 1,

    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 -20.
     */
    RESCUER_NICE_LEVEL  = -20,
    HIGHPRI_NICE_LEVEL  = -20,
};

/*
 * 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: gcwq->lock protected.  Access with gcwq->lock held.
 *
 * X: During normal operation, modification requires gcwq->lock and
 *    should be done only from local cpu.  Either disabling preemption
 *    on local cpu or grabbing gcwq->lock is enough for read access.
 *    If GCWQ_DISASSOCIATED is set, it's identical to L.
 *
 * F: wq->flush_mutex protected.
 *
 * W: workqueue_lock protected.
 */

struct global_cwq;
struct worker_pool;

/*
 * The poor guys doing the actual heavy lifting.  All on-duty workers
 * are either serving the manager role, on idle list or on busy hash.
 */
struct worker {
    /* on idle list while idle, on busy hash table while busy */
    union {
        struct list_head    entry;  /* L: while idle */
        struct hlist_node   hentry; /* L: while busy */
    };

    struct work_struct  *current_work;  /* L: work being processed */
    struct cpu_workqueue_struct *current_cwq; /* L: current_work's cwq */
    struct list_head    scheduled;  /* L: scheduled works */
    struct task_struct  *task;      /* I: worker task */
    struct worker_pool  *pool;      /* I: the associated pool */
    /* 64 bytes boundary on 64bit, 32 on 32bit */
    unsigned long       last_active;    /* L: last active timestamp */
    unsigned int        flags;      /* X: flags */
    int         id;     /* I: worker id */

    /* for rebinding worker to CPU */
    struct work_struct  rebind_work;    /* L: for busy worker */
};

struct worker_pool {
    struct global_cwq   *gcwq;      /* I: the owning gcwq */
    unsigned int        flags;      /* X: flags */

    struct list_head    worklist;   /* L: list of pending works */
    int         nr_workers; /* L: total number of workers */

    /* nr_idle includes the ones off idle_list for rebinding */
    int         nr_idle;    /* L: currently idle ones */

    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 */

    struct mutex        assoc_mutex;    /* protect GCWQ_DISASSOCIATED */
    struct ida      worker_ida; /* L: for worker IDs */
};

/*
 * Global per-cpu workqueue.  There's one and only one for each cpu
 * and all works are queued and processed here regardless of their
 * target workqueues.
 */
struct global_cwq {
    spinlock_t      lock;       /* the gcwq lock */
    unsigned int        cpu;        /* I: the associated cpu */
    unsigned int        flags;      /* L: GCWQ_* flags */

    /* workers are chained either in busy_hash or pool idle_list */
    struct hlist_head   busy_hash[BUSY_WORKER_HASH_SIZE];
                        /* L: hash of busy workers */

    struct worker_pool  pools[NR_WORKER_POOLS];
                        /* normal and highpri pools */
} ____cacheline_aligned_in_smp;

/*
 * The per-CPU workqueue.  The lower WORK_STRUCT_FLAG_BITS of
 * work_struct->data are used for flags and thus cwqs need to be
 * aligned at two's power of the number of flag bits.
 */
struct cpu_workqueue_struct {
    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         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 */
};

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

/*
 * All cpumasks are assumed to be always set on UP and thus can't be
 * used to determine whether there's something to be done.
 */
#ifdef CONFIG_SMP
typedef cpumask_var_t mayday_mask_t;
#define mayday_test_and_set_cpu(cpu, mask)  \
    cpumask_test_and_set_cpu((cpu), (mask))
#define mayday_clear_cpu(cpu, mask)     cpumask_clear_cpu((cpu), (mask))
#define for_each_mayday_cpu(cpu, mask)      for_each_cpu((cpu), (mask))
#define alloc_mayday_mask(maskp, gfp)       zalloc_cpumask_var((maskp), (gfp))
#define free_mayday_mask(mask)          free_cpumask_var((mask))
#else
typedef unsigned long mayday_mask_t;
#define mayday_test_and_set_cpu(cpu, mask)  test_and_set_bit(0, &(mask))
#define mayday_clear_cpu(cpu, mask)     clear_bit(0, &(mask))
#define for_each_mayday_cpu(cpu, mask)      if ((cpu) = 0, (mask))
#define alloc_mayday_mask(maskp, gfp)       true
#define free_mayday_mask(mask)          do { } while (0)
#endif

/*
 * The externally visible workqueue abstraction is an array of
 * per-CPU workqueues:
 */
struct workqueue_struct {
    unsigned int        flags;      /* W: WQ_* flags */
    union {
        struct cpu_workqueue_struct __percpu    *pcpu;
        struct cpu_workqueue_struct     *single;
        unsigned long               v;
    } cpu_wq;               /* I: cwq's */
    struct list_head    list;       /* W: list of all workqueues */

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

    mayday_mask_t       mayday_mask;    /* cpus requesting rescue */
    struct worker       *rescuer;   /* I: rescue worker */

    int         nr_drainers;    /* W: drain in progress */
    int         saved_max_active; /* W: saved cwq max_active */
#ifdef CONFIG_LOCKDEP
    struct lockdep_map  lockdep_map;
#endif
    char            name[];     /* I: workqueue name */
};

struct workqueue_struct *system_wq __read_mostly;
EXPORT_SYMBOL_GPL(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);

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

#define for_each_worker_pool(pool, gcwq)                \
    for ((pool) = &(gcwq)->pools[0];                \
         (pool) < &(gcwq)->pools[NR_WORKER_POOLS]; (pool)++)

#define for_each_busy_worker(worker, i, pos, gcwq)          \
    for (i = 0; i < BUSY_WORKER_HASH_SIZE; i++)         \
        hlist_for_each_entry(worker, pos, &gcwq->busy_hash[i], hentry)

static inline int __next_gcwq_cpu(int cpu, const struct cpumask *mask,
                  unsigned int sw)
{
    if (cpu < nr_cpu_ids) {
        if (sw & 1) {
            cpu = cpumask_next(cpu, mask);
            if (cpu < nr_cpu_ids)
                return cpu;
        }
        if (sw & 2)
            return WORK_CPU_UNBOUND;
    }
    return WORK_CPU_NONE;
}

static inline int __next_wq_cpu(int cpu, const struct cpumask *mask,
                struct workqueue_struct *wq)
{
    return __next_gcwq_cpu(cpu, mask, !(wq->flags & WQ_UNBOUND) ? 1 : 2);
}

/*
 * CPU iterators
 *
 * An extra gcwq is defined for an invalid cpu number
 * (WORK_CPU_UNBOUND) to host workqueues which are not bound to any
 * specific CPU.  The following iterators are similar to
 * for_each_*_cpu() iterators but also considers the unbound gcwq.
 *
 * for_each_gcwq_cpu()      : possible CPUs + WORK_CPU_UNBOUND
 * for_each_online_gcwq_cpu()   : online CPUs + WORK_CPU_UNBOUND
 * for_each_cwq_cpu()       : possible CPUs for bound workqueues,
 *                WORK_CPU_UNBOUND for unbound workqueues
 */
#define for_each_gcwq_cpu(cpu)                      \
    for ((cpu) = __next_gcwq_cpu(-1, cpu_possible_mask, 3);     \
         (cpu) < WORK_CPU_NONE;                 \
         (cpu) = __next_gcwq_cpu((cpu), cpu_possible_mask, 3))

#define for_each_online_gcwq_cpu(cpu)                   \
    for ((cpu) = __next_gcwq_cpu(-1, cpu_online_mask, 3);       \
         (cpu) < WORK_CPU_NONE;                 \
         (cpu) = __next_gcwq_cpu((cpu), cpu_online_mask, 3))

#define for_each_cwq_cpu(cpu, wq)                   \
    for ((cpu) = __next_wq_cpu(-1, cpu_possible_mask, (wq));    \
         (cpu) < WORK_CPU_NONE;                 \
         (cpu) = __next_wq_cpu((cpu), cpu_possible_mask, (wq)))

#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;
}

/*
 * fixup_init is called when:
 * - an active object is initialized
 */
static int 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 1;
    default:
        return 0;
    }
}

/*
 * fixup_activate is called when:
 * - an active object is activated
 * - an unknown object is activated (might be a statically initialized object)
 */
static int work_fixup_activate(void *addr, enum debug_obj_state state)
{
    struct work_struct *work = addr;

    switch (state) {

    case ODEBUG_STATE_NOTAVAILABLE:
        /*
         * This is not really a fixup. The work struct was
         * statically initialized. We just make sure that it
         * is tracked in the object tracker.
         */
        if (test_bit(WORK_STRUCT_STATIC_BIT, work_data_bits(work))) {
            debug_object_init(work, &work_debug_descr);
            debug_object_activate(work, &work_debug_descr);
            return 0;
        }
        WARN_ON_ONCE(1);
        return 0;

    case ODEBUG_STATE_ACTIVE:
        WARN_ON(1);

    default:
        return 0;
    }
}

/*
 * fixup_free is called when:
 * - an active object is freed
 */
static int 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 1;
    default:
        return 0;
    }
}

static struct debug_obj_descr work_debug_descr = {
    .name       = "work_struct",
    .debug_hint = work_debug_hint,
    .fixup_init = work_fixup_init,
    .fixup_activate = work_fixup_activate,
    .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);

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

/* Serializes the accesses to the list of workqueues. */
static DEFINE_SPINLOCK(workqueue_lock);
static LIST_HEAD(workqueues);
static bool workqueue_freezing;     /* W: have wqs started freezing? */

/*
 * The almighty global cpu workqueues.  nr_running is the only field
 * which is expected to be used frequently by other cpus via
 * try_to_wake_up().  Put it in a separate cacheline.
 */
static DEFINE_PER_CPU(struct global_cwq, global_cwq);
static DEFINE_PER_CPU_SHARED_ALIGNED(atomic_t, pool_nr_running[NR_WORKER_POOLS]);

/*
 * Global cpu workqueue and nr_running counter for unbound gcwq.  The
 * gcwq is always online, has GCWQ_DISASSOCIATED set, and all its
 * workers have WORKER_UNBOUND set.
 */
static struct global_cwq unbound_global_cwq;
static atomic_t unbound_pool_nr_running[NR_WORKER_POOLS] = {
    [0 ... NR_WORKER_POOLS - 1] = ATOMIC_INIT(0),   /* always 0 */
};

static int worker_thread(void *__worker);

static int worker_pool_pri(struct worker_pool *pool)
{
    return pool - pool->gcwq->pools;
}

static struct global_cwq *get_gcwq(unsigned int cpu)
{
    if (cpu != WORK_CPU_UNBOUND)
        return &per_cpu(global_cwq, cpu);
    else
        return &unbound_global_cwq;
}

static atomic_t *get_pool_nr_running(struct worker_pool *pool)
{
    int cpu = pool->gcwq->cpu;
    int idx = worker_pool_pri(pool);

    if (cpu != WORK_CPU_UNBOUND)
        return &per_cpu(pool_nr_running, cpu)[idx];
    else
        return &unbound_pool_nr_running[idx];
}

static struct cpu_workqueue_struct *get_cwq(unsigned int cpu,
                        struct workqueue_struct *wq)
{
    if (!(wq->flags & WQ_UNBOUND)) {
        if (likely(cpu < nr_cpu_ids))
            return per_cpu_ptr(wq->cpu_wq.pcpu, cpu);
    } else if (likely(cpu == WORK_CPU_UNBOUND))
        return wq->cpu_wq.single;
    return NULL;
}

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_CWQ is set and non flag bits of a work's data
 * contain the pointer to the queued cwq.  Once execution starts, the flag
 * is cleared and the high bits contain OFFQ flags and CPU number.
 *
 * set_work_cwq(), set_work_cpu_and_clear_pending(), mark_work_canceling()
 * and clear_work_data() can be used to set the cwq, cpu or clear
 * work->data.  These functions should only be called while the work is
 * owned - ie. while the PENDING bit is set.
 *
 * get_work_[g]cwq() can be used to obtain the gcwq or cwq corresponding to
 * a work.  gcwq is available once the work has been queued anywhere after
 * initialization until it is sync canceled.  cwq 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)
{
    BUG_ON(!work_pending(work));
    atomic_long_set(&work->data, data | flags | work_static(work));
}

static void set_work_cwq(struct work_struct *work,
             struct cpu_workqueue_struct *cwq,
             unsigned long extra_flags)
{
    set_work_data(work, (unsigned long)cwq,
              WORK_STRUCT_PENDING | WORK_STRUCT_CWQ | extra_flags);
}

static void set_work_cpu_and_clear_pending(struct work_struct *work,
                       unsigned int cpu)
{
    /*
     * 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)cpu << WORK_OFFQ_CPU_SHIFT, 0);
}

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

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

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

static struct global_cwq *get_work_gcwq(struct work_struct *work)
{
    unsigned long data = atomic_long_read(&work->data);
    unsigned int cpu;

    if (data & WORK_STRUCT_CWQ)
        return ((struct cpu_workqueue_struct *)
            (data & WORK_STRUCT_WQ_DATA_MASK))->pool->gcwq;

    cpu = data >> WORK_OFFQ_CPU_SHIFT;
    if (cpu == WORK_CPU_NONE)
        return NULL;

    BUG_ON(cpu >= nr_cpu_ids && cpu != WORK_CPU_UNBOUND);
    return get_gcwq(cpu);
}

static void mark_work_canceling(struct work_struct *work)
{
    struct global_cwq *gcwq = get_work_gcwq(work);
    unsigned long cpu = gcwq ? gcwq->cpu : WORK_CPU_NONE;

    set_work_data(work, (cpu << WORK_OFFQ_CPU_SHIFT) | 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_CWQ) && (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 gcwq->lock held.
 */

static bool __need_more_worker(struct worker_pool *pool)
{
    return !atomic_read(get_pool_nr_running(pool));
}

/*
 * 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 gcwq 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)
{
    atomic_t *nr_running = get_pool_nr_running(pool);

    return !list_empty(&pool->worklist) && atomic_read(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 I need to be the manager? */
static bool need_to_manage_workers(struct worker_pool *pool)
{
    return need_to_create_worker(pool) ||
        (pool->flags & POOL_MANAGE_WORKERS);
}

/* 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_MANAGING_WORKERS;
    int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
    int nr_busy = pool->nr_workers - nr_idle;

    /*
     * nr_idle and idle_list may disagree if idle rebinding is in
     * progress.  Never return %true if idle_list is empty.
     */
    if (list_empty(&pool->idle_list))
        return false;

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

/*
 * Wake up functions.
 */

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

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

static void wake_up_worker(struct worker_pool *pool)
{
    struct worker *worker = first_worker(pool);

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

void wq_worker_waking_up(struct task_struct *task, unsigned int cpu)
{
    struct worker *worker = kthread_data(task);

    if (!(worker->flags & WORKER_NOT_RUNNING))
        atomic_inc(get_pool_nr_running(worker->pool));
}

struct task_struct *wq_worker_sleeping(struct task_struct *task,
                       unsigned int cpu)
{
    struct worker *worker = kthread_data(task), *to_wakeup = NULL;
    struct worker_pool *pool = worker->pool;
    atomic_t *nr_running = get_pool_nr_running(pool);

    if (worker->flags & WORKER_NOT_RUNNING)
        return NULL;

    /* this can only happen on the local cpu */
    BUG_ON(cpu != raw_smp_processor_id());

    /*
     * 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 gcwq
     * lock is safe.
     */
    if (atomic_dec_and_test(nr_running) && !list_empty(&pool->worklist))
        to_wakeup = first_worker(pool);
    return to_wakeup ? to_wakeup->task : NULL;
}

static inline void worker_set_flags(struct worker *worker, unsigned int flags,
                    bool wakeup)
{
    struct worker_pool *pool = worker->pool;

    WARN_ON_ONCE(worker->task != current);

    /*
     * If transitioning into NOT_RUNNING, adjust nr_running and
     * wake up an idle worker as necessary if requested by
     * @wakeup.
     */
    if ((flags & WORKER_NOT_RUNNING) &&
        !(worker->flags & WORKER_NOT_RUNNING)) {
        atomic_t *nr_running = get_pool_nr_running(pool);

        if (wakeup) {
            if (atomic_dec_and_test(nr_running) &&
                !list_empty(&pool->worklist))
                wake_up_worker(pool);
        } else
            atomic_dec(nr_running);
    }

    worker->flags |= flags;
}

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(get_pool_nr_running(pool));
}

static struct hlist_head *busy_worker_head(struct global_cwq *gcwq,
                       struct work_struct *work)
{
    const int base_shift = ilog2(sizeof(struct work_struct));
    unsigned long v = (unsigned long)work;

    /* simple shift and fold hash, do we need something better? */
    v >>= base_shift;
    v += v >> BUSY_WORKER_HASH_ORDER;
    v &= BUSY_WORKER_HASH_MASK;

    return &gcwq->busy_hash[v];
}

static struct worker *__find_worker_executing_work(struct global_cwq *gcwq,
                           struct hlist_head *bwh,
                           struct work_struct *work)
{
    struct worker *worker;
    struct hlist_node *tmp;

    hlist_for_each_entry(worker, tmp, bwh, hentry)
        if (worker->current_work == work)
            return worker;
    return NULL;
}

static struct worker *find_worker_executing_work(struct global_cwq *gcwq,
                         struct work_struct *work)
{
    return __find_worker_executing_work(gcwq, busy_worker_head(gcwq, work),
                        work);
}

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;
}

static void cwq_activate_delayed_work(struct work_struct *work)
{
    struct cpu_workqueue_struct *cwq = get_work_cwq(work);

    trace_workqueue_activate_work(work);
    move_linked_works(work, &cwq->pool->worklist, NULL);
    __clear_bit(WORK_STRUCT_DELAYED_BIT, work_data_bits(work));
    cwq->nr_active++;
}

static void cwq_activate_first_delayed(struct cpu_workqueue_struct *cwq)
{
    struct work_struct *work = list_first_entry(&cwq->delayed_works,
                            struct work_struct, entry);

    cwq_activate_delayed_work(work);
}

static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color)
{
    /* ignore uncolored works */
    if (color == WORK_NO_COLOR)
        return;

    cwq->nr_in_flight[color]--;

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

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

    /* are there still in-flight works? */
    if (cwq->nr_in_flight[color])
        return;

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

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

static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
                   unsigned long *flags)
{
    struct global_cwq *gcwq;

    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;

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

    spin_lock(&gcwq->lock);
    if (!list_empty(&work->entry)) {
        /*
         * This work is queued, but perhaps we locked the wrong gcwq.
         * In that case we must see the new value after rmb(), see
         * insert_work()->wmb().
         */
        smp_rmb();
        if (gcwq == get_work_gcwq(work)) {
            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
             * cwq->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)
                cwq_activate_delayed_work(work);

            list_del_init(&work->entry);
            cwq_dec_nr_in_flight(get_work_cwq(work),
                get_work_color(work));

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

static void insert_work(struct cpu_workqueue_struct *cwq,
            struct work_struct *work, struct list_head *head,
            unsigned int extra_flags)
{
    struct worker_pool *pool = cwq->pool;

    /* we own @work, set data and link */
    set_work_cwq(work, cwq, extra_flags);

    /*
     * Ensure that we get the right work->data if we see the
     * result of list_add() below, see try_to_grab_pending().
     */
    smp_wmb();

    list_add_tail(&work->entry, head);

    /*
     * Ensure either worker_sched_deactivated() 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.  This is rather expensive and should only be used from
 * cold paths.
 */
static bool is_chained_work(struct workqueue_struct *wq)
{
    unsigned long flags;
    unsigned int cpu;

    for_each_gcwq_cpu(cpu) {
        struct global_cwq *gcwq = get_gcwq(cpu);
        struct worker *worker;
        struct hlist_node *pos;
        int i;

        spin_lock_irqsave(&gcwq->lock, flags);
        for_each_busy_worker(worker, i, pos, gcwq) {
            if (worker->task != current)
                continue;
            spin_unlock_irqrestore(&gcwq->lock, flags);
            /*
             * I'm @worker, no locking necessary.  See if @work
             * is headed to the same workqueue.
             */
            return worker->current_cwq->wq == wq;
        }
        spin_unlock_irqrestore(&gcwq->lock, flags);
    }
    return false;
}

static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
             struct work_struct *work)
{
    struct global_cwq *gcwq;
    struct cpu_workqueue_struct *cwq;
    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.
     */
    WARN_ON_ONCE(!irqs_disabled());

    debug_work_activate(work);

    /* if dying, only works from the same workqueue are allowed */
    if (unlikely(wq->flags & WQ_DRAINING) &&
        WARN_ON_ONCE(!is_chained_work(wq)))
        return;

    /* determine gcwq to use */
    if (!(wq->flags & WQ_UNBOUND)) {
        struct global_cwq *last_gcwq;

        if (cpu == WORK_CPU_UNBOUND)
            cpu = raw_smp_processor_id();

        /*
         * It's multi cpu.  If @work was previously on a different
         * cpu, it might still be running there, in which case the
         * work needs to be queued on that cpu to guarantee
         * non-reentrancy.
         */
        gcwq = get_gcwq(cpu);
        last_gcwq = get_work_gcwq(work);

        if (last_gcwq && last_gcwq != gcwq) {
            struct worker *worker;

            spin_lock(&last_gcwq->lock);

            worker = find_worker_executing_work(last_gcwq, work);

            if (worker && worker->current_cwq->wq == wq)
                gcwq = last_gcwq;
            else {
                /* meh... not running there, queue here */
                spin_unlock(&last_gcwq->lock);
                spin_lock(&gcwq->lock);
            }
        } else {
            spin_lock(&gcwq->lock);
        }
    } else {
        gcwq = get_gcwq(WORK_CPU_UNBOUND);
        spin_lock(&gcwq->lock);
    }

    /* gcwq determined, get cwq and queue */
    cwq = get_cwq(gcwq->cpu, wq);
    trace_workqueue_queue_work(req_cpu, cwq, work);

    if (WARN_ON(!list_empty(&work->entry))) {
        spin_unlock(&gcwq->lock);
        return;
    }

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

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

    insert_work(cwq, work, worklist, work_flags);

    spin_unlock(&gcwq->lock);
}

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_GPL(queue_work_on);

bool queue_work(struct workqueue_struct *wq, struct work_struct *work)
{
    return queue_work_on(WORK_CPU_UNBOUND, wq, work);
}
EXPORT_SYMBOL_GPL(queue_work);

void delayed_work_timer_fn(unsigned long __data)
{
    struct delayed_work *dwork = (struct delayed_work *)__data;
    struct cpu_workqueue_struct *cwq = get_work_cwq(&dwork->work);

    /* should have been called from irqsafe timer with irq already off */
    __queue_work(dwork->cpu, cwq->wq, &dwork->work);
}
EXPORT_SYMBOL_GPL(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;
    unsigned int lcpu;

    WARN_ON_ONCE(timer->function != delayed_work_timer_fn ||
             timer->data != (unsigned long)dwork);
    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;
    }

    timer_stats_timer_set_start_info(&dwork->timer);

    /*
     * This stores cwq for the moment, for the timer_fn.  Note that the
     * work's gcwq is preserved to allow reentrance detection for
     * delayed works.
     */
    if (!(wq->flags & WQ_UNBOUND)) {
        struct global_cwq *gcwq = get_work_gcwq(work);

        /*
         * If we cannot get the last gcwq from @work directly,
         * select the last CPU such that it avoids unnecessarily
         * triggering non-reentrancy check in __queue_work().
         */
        lcpu = cpu;
        if (gcwq)
            lcpu = gcwq->cpu;
        if (lcpu == WORK_CPU_UNBOUND)
            lcpu = raw_smp_processor_id();
    } else {
        lcpu = WORK_CPU_UNBOUND;
    }

    set_work_cwq(work, get_cwq(lcpu, wq), 0);

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

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

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_GPL(queue_delayed_work_on);

bool queue_delayed_work(struct workqueue_struct *wq,
            struct delayed_work *dwork, unsigned long delay)
{
    return queue_delayed_work_on(WORK_CPU_UNBOUND, wq, dwork, delay);
}
EXPORT_SYMBOL_GPL(queue_delayed_work);

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);

bool mod_delayed_work(struct workqueue_struct *wq, struct delayed_work *dwork,
              unsigned long delay)
{
    return mod_delayed_work_on(WORK_CPU_UNBOUND, wq, dwork, delay);
}
EXPORT_SYMBOL_GPL(mod_delayed_work);

static void worker_enter_idle(struct worker *worker)
{
    struct worker_pool *pool = worker->pool;
    struct global_cwq *gcwq = pool->gcwq;

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

    /* can't use worker_set_flags(), also called from start_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 gcwq_unbind_fn() releases
     * gcwq->lock between setting %WORKER_UNBOUND and zapping
     * nr_running, the warning may trigger spuriously.  Check iff
     * unbind is not in progress.
     */
    WARN_ON_ONCE(!(gcwq->flags & GCWQ_DISASSOCIATED) &&
             pool->nr_workers == pool->nr_idle &&
             atomic_read(get_pool_nr_running(pool)));
}

static void worker_leave_idle(struct worker *worker)
{
    struct worker_pool *pool = worker->pool;

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

static bool worker_maybe_bind_and_lock(struct worker *worker)
__acquires(&gcwq->lock)
{
    struct global_cwq *gcwq = worker->pool->gcwq;
    struct task_struct *task = worker->task;

    while (true) {
        /*
         * The following call may fail, succeed or succeed
         * without actually migrating the task to the cpu if
         * it races with cpu hotunplug operation.  Verify
         * against GCWQ_DISASSOCIATED.
         */
        if (!(gcwq->flags & GCWQ_DISASSOCIATED))
            set_cpus_allowed_ptr(task, get_cpu_mask(gcwq->cpu));

        spin_lock_irq(&gcwq->lock);
        if (gcwq->flags & GCWQ_DISASSOCIATED)
            return false;
        if (task_cpu(task) == gcwq->cpu &&
            cpumask_equal(&current->cpus_allowed,
                  get_cpu_mask(gcwq->cpu)))
            return true;
        spin_unlock_irq(&gcwq->lock);

        /*
         * We've raced with CPU hot[un]plug.  Give it a breather
         * and retry migration.  cond_resched() is required here;
         * otherwise, we might deadlock against cpu_stop trying to
         * bring down the CPU on non-preemptive kernel.
         */
        cpu_relax();
        cond_resched();
    }
}

/*
 * Rebind an idle @worker to its CPU.  worker_thread() will test
 * list_empty(@worker->entry) before leaving idle and call this function.
 */
static void idle_worker_rebind(struct worker *worker)
{
    struct global_cwq *gcwq = worker->pool->gcwq;

    /* CPU may go down again inbetween, clear UNBOUND only on success */
    if (worker_maybe_bind_and_lock(worker))
        worker_clr_flags(worker, WORKER_UNBOUND);

    /* rebind complete, become available again */
    list_add(&worker->entry, &worker->pool->idle_list);
    spin_unlock_irq(&gcwq->lock);
}

/*
 * Function for @worker->rebind.work used to rebind unbound busy workers to
 * the associated cpu which is coming back online.  This is scheduled by
 * cpu up but can race with other cpu hotplug operations and may be
 * executed twice without intervening cpu down.
 */
static void busy_worker_rebind_fn(struct work_struct *work)
{
    struct worker *worker = container_of(work, struct worker, rebind_work);
    struct global_cwq *gcwq = worker->pool->gcwq;

    if (worker_maybe_bind_and_lock(worker))
        worker_clr_flags(worker, WORKER_UNBOUND);

    spin_unlock_irq(&gcwq->lock);
}

static void rebind_workers(struct global_cwq *gcwq)
{
    struct worker_pool *pool;
    struct worker *worker, *n;
    struct hlist_node *pos;
    int i;

    lockdep_assert_held(&gcwq->lock);

    for_each_worker_pool(pool, gcwq)
        lockdep_assert_held(&pool->assoc_mutex);

    /* dequeue and kick idle ones */
    for_each_worker_pool(pool, gcwq) {
        list_for_each_entry_safe(worker, n, &pool->idle_list, entry) {
            /*
             * idle workers should be off @pool->idle_list
             * until rebind is complete to avoid receiving
             * premature local wake-ups.
             */
            list_del_init(&worker->entry);

            /*
             * worker_thread() will see the above dequeuing
             * and call idle_worker_rebind().
             */
            wake_up_process(worker->task);
        }
    }

    /* rebind busy workers */
    for_each_busy_worker(worker, i, pos, gcwq) {
        struct work_struct *rebind_work = &worker->rebind_work;
        struct workqueue_struct *wq;

        if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
                     work_data_bits(rebind_work)))
            continue;

        debug_work_activate(rebind_work);

        /*
         * wq doesn't really matter but let's keep @worker->pool
         * and @cwq->pool consistent for sanity.
         */
        if (worker_pool_pri(worker->pool))
            wq = system_highpri_wq;
        else
            wq = system_wq;

        insert_work(get_cwq(gcwq->cpu, wq), rebind_work,
            worker->scheduled.next,
            work_color_to_flags(WORK_NO_COLOR));
    }
}

static struct worker *alloc_worker(void)
{
    struct worker *worker;

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

static struct worker *create_worker(struct worker_pool *pool)
{
    struct global_cwq *gcwq = pool->gcwq;
    const char *pri = worker_pool_pri(pool) ? "H" : "";
    struct worker *worker = NULL;
    int id = -1;

    spin_lock_irq(&gcwq->lock);
    while (ida_get_new(&pool->worker_ida, &id)) {
        spin_unlock_irq(&gcwq->lock);
        if (!ida_pre_get(&pool->worker_ida, GFP_KERNEL))
            goto fail;
        spin_lock_irq(&gcwq->lock);
    }
    spin_unlock_irq(&gcwq->lock);

    worker = alloc_worker();
    if (!worker)
        goto fail;

    worker->pool = pool;
    worker->id = id;

    if (gcwq->cpu != WORK_CPU_UNBOUND)
        worker->task = kthread_create_on_node(worker_thread,
                    worker, cpu_to_node(gcwq->cpu),
                    "kworker/%u:%d%s", gcwq->cpu, id, pri);
    else
        worker->task = kthread_create(worker_thread, worker,
                          "kworker/u:%d%s", id, pri);
    if (IS_ERR(worker->task))
        goto fail;

    if (worker_pool_pri(pool))
        set_user_nice(worker->task, HIGHPRI_NICE_LEVEL);

    /*
     * Determine CPU binding of the new worker depending on
     * %GCWQ_DISASSOCIATED.  The caller is responsible for ensuring the
     * flag remains stable across this function.  See the comments
     * above the flag definition for details.
     *
     * As an unbound worker may later become a regular one if CPU comes
     * online, make sure every worker has %PF_THREAD_BOUND set.
     */
    if (!(gcwq->flags & GCWQ_DISASSOCIATED)) {
        kthread_bind(worker->task, gcwq->cpu);
    } else {
        worker->task->flags |= PF_THREAD_BOUND;
        worker->flags |= WORKER_UNBOUND;
    }

    return worker;
fail:
    if (id >= 0) {
        spin_lock_irq(&gcwq->lock);
        ida_remove(&pool->worker_ida, id);
        spin_unlock_irq(&gcwq->lock);
    }
    kfree(worker);
    return NULL;
}

static void start_worker(struct worker *worker)
{
    worker->flags |= WORKER_STARTED;
    worker->pool->nr_workers++;
    worker_enter_idle(worker);
    wake_up_process(worker->task);
}

static void destroy_worker(struct worker *worker)
{
    struct worker_pool *pool = worker->pool;
    struct global_cwq *gcwq = pool->gcwq;
    int id = worker->id;

    /* sanity check frenzy */
    BUG_ON(worker->current_work);
    BUG_ON(!list_empty(&worker->scheduled));

    if (worker->flags & WORKER_STARTED)
        pool->nr_workers--;
    if (worker->flags & WORKER_IDLE)
        pool->nr_idle--;

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

    spin_unlock_irq(&gcwq->lock);

    kthread_stop(worker->task);
    kfree(worker);

    spin_lock_irq(&gcwq->lock);
    ida_remove(&pool->worker_ida, id);
}

static void idle_worker_timeout(unsigned long __pool)
{
    struct worker_pool *pool = (void *)__pool;
    struct global_cwq *gcwq = pool->gcwq;

    spin_lock_irq(&gcwq->lock);

    if (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);
        else {
            /* it's been idle for too long, wake up manager */
            pool->flags |= POOL_MANAGE_WORKERS;
            wake_up_worker(pool);
        }
    }

    spin_unlock_irq(&gcwq->lock);
}

static bool send_mayday(struct work_struct *work)
{
    struct cpu_workqueue_struct *cwq = get_work_cwq(work);
    struct workqueue_struct *wq = cwq->wq;
    unsigned int cpu;

    if (!(wq->flags & WQ_RESCUER))
        return false;

    /* mayday mayday mayday */
    cpu = cwq->pool->gcwq->cpu;
    /* WORK_CPU_UNBOUND can't be set in cpumask, use cpu 0 instead */
    if (cpu == WORK_CPU_UNBOUND)
        cpu = 0;
    if (!mayday_test_and_set_cpu(cpu, wq->mayday_mask))
        wake_up_process(wq->rescuer->task);
    return true;
}

static void gcwq_mayday_timeout(unsigned long __pool)
{
    struct worker_pool *pool = (void *)__pool;
    struct global_cwq *gcwq = pool->gcwq;
    struct work_struct *work;

    spin_lock_irq(&gcwq->lock);

    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_irq(&gcwq->lock);

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

static bool maybe_create_worker(struct worker_pool *pool)
__releases(&gcwq->lock)
__acquires(&gcwq->lock)
{
    struct global_cwq *gcwq = pool->gcwq;

    if (!need_to_create_worker(pool))
        return false;
restart:
    spin_unlock_irq(&gcwq->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) {
        struct worker *worker;

        worker = create_worker(pool);
        if (worker) {
            del_timer_sync(&pool->mayday_timer);
            spin_lock_irq(&gcwq->lock);
            start_worker(worker);
            BUG_ON(need_to_create_worker(pool));
            return true;
        }

        if (!need_to_create_worker(pool))
            break;

        __set_current_state(TASK_INTERRUPTIBLE);
        schedule_timeout(CREATE_COOLDOWN);

        if (!need_to_create_worker(pool))
            break;
    }

    del_timer_sync(&pool->mayday_timer);
    spin_lock_irq(&gcwq->lock);
    if (need_to_create_worker(pool))
        goto restart;
    return true;
}

static bool maybe_destroy_workers(struct worker_pool *pool)
{
    bool ret = false;

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

        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);
        ret = true;
    }

    return ret;
}

static bool manage_workers(struct worker *worker)
{
    struct worker_pool *pool = worker->pool;
    bool ret = false;

    if (pool->flags & POOL_MANAGING_WORKERS)
        return ret;

    pool->flags |= POOL_MANAGING_WORKERS;

    /*
     * To simplify both worker management and CPU hotplug, hold off
     * management while hotplug is in progress.  CPU hotplug path can't
     * grab %POOL_MANAGING_WORKERS to achieve this because that can
     * lead to idle worker depletion (all become busy thinking someone
     * else is managing) which in turn can result in deadlock under
     * extreme circumstances.  Use @pool->assoc_mutex to synchronize
     * manager against CPU hotplug.
     *
     * assoc_mutex would always be free unless CPU hotplug is in
     * progress.  trylock first without dropping @gcwq->lock.
     */
    if (unlikely(!mutex_trylock(&pool->assoc_mutex))) {
        spin_unlock_irq(&pool->gcwq->lock);
        mutex_lock(&pool->assoc_mutex);
        /*
         * CPU hotplug could have happened while we were waiting
         * for assoc_mutex.  Hotplug itself can't handle us
         * because manager isn't either on idle or busy list, and
         * @gcwq's state and ours could have deviated.
         *
         * As hotplug is now excluded via assoc_mutex, we can
         * simply try to bind.  It will succeed or fail depending
         * on @gcwq's current state.  Try it and adjust
         * %WORKER_UNBOUND accordingly.
         */
        if (worker_maybe_bind_and_lock(worker))
            worker->flags &= ~WORKER_UNBOUND;
        else
            worker->flags |= WORKER_UNBOUND;

        ret = true;
    }

    pool->flags &= ~POOL_MANAGE_WORKERS;

    /*
     * Destroy and then create so that may_start_working() is true
     * on return.
     */
    ret |= maybe_destroy_workers(pool);
    ret |= maybe_create_worker(pool);

    pool->flags &= ~POOL_MANAGING_WORKERS;
    mutex_unlock(&pool->assoc_mutex);
    return ret;
}

static void process_one_work(struct worker *worker, struct work_struct *work)
__releases(&gcwq->lock)
__acquires(&gcwq->lock)
{
    struct cpu_workqueue_struct *cwq = get_work_cwq(work);
    struct worker_pool *pool = worker->pool;
    struct global_cwq *gcwq = pool->gcwq;
    struct hlist_head *bwh = busy_worker_head(gcwq, work);
    bool cpu_intensive = cwq->wq->flags & WQ_CPU_INTENSIVE;
    work_func_t f = work->func;
    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.  DISASSOCIATED test is
     * necessary to avoid spurious warnings from rescuers servicing the
     * unbound or a disassociated gcwq.
     */
    WARN_ON_ONCE(!(worker->flags & WORKER_UNBOUND) &&
             !(gcwq->flags & GCWQ_DISASSOCIATED) &&
             raw_smp_processor_id() != gcwq->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(gcwq, bwh, work);
    if (unlikely(collision)) {
        move_linked_works(work, &collision->scheduled, NULL);
        return;
    }

    /* claim and dequeue */
    debug_work_deactivate(work);
    hlist_add_head(&worker->hentry, bwh);
    worker->current_work = work;
    worker->current_cwq = cwq;
    work_color = get_work_color(work);

    list_del_init(&work->entry);

    /*
     * CPU intensive works don't participate in concurrency
     * management.  They're the scheduler's responsibility.
     */
    if (unlikely(cpu_intensive))
        worker_set_flags(worker, WORKER_CPU_INTENSIVE, true);

    /*
     * Unbound gcwq isn't concurrency managed and work items should be
     * executed ASAP.  Wake up another worker if necessary.
     */
    if ((worker->flags & WORKER_UNBOUND) && need_more_worker(pool))
        wake_up_worker(pool);

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

    spin_unlock_irq(&gcwq->lock);

    lock_map_acquire_read(&cwq->wq->lockdep_map);
    lock_map_acquire(&lockdep_map);
    trace_workqueue_execute_start(work);
    f(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(&cwq->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: %pf\n",
               current->comm, preempt_count(), task_pid_nr(current), f);
        debug_show_held_locks(current);
        dump_stack();
    }

    spin_lock_irq(&gcwq->lock);

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

    /* we're done with it, release */
    hlist_del_init(&worker->hentry);
    worker->current_work = NULL;
    worker->current_cwq = NULL;
    cwq_dec_nr_in_flight(cwq, work_color);
}

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 int worker_thread(void *__worker)
{
    struct worker *worker = __worker;
    struct worker_pool *pool = worker->pool;
    struct global_cwq *gcwq = pool->gcwq;

    /* tell the scheduler that this is a workqueue worker */
    worker->task->flags |= PF_WQ_WORKER;
woke_up:
    spin_lock_irq(&gcwq->lock);

    /* we are off idle list if destruction or rebind is requested */
    if (unlikely(list_empty(&worker->entry))) {
        spin_unlock_irq(&gcwq->lock);

        /* if DIE is set, destruction is requested */
        if (worker->flags & WORKER_DIE) {
            worker->task->flags &= ~PF_WQ_WORKER;
            return 0;
        }

        /* otherwise, rebind */
        idle_worker_rebind(worker);
        goto woke_up;
    }

    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.
     */
    BUG_ON(!list_empty(&worker->scheduled));

    /*
     * When control reaches this point, we're guaranteed to have
     * at least one idle worker or that someone else has already
     * assumed the manager role.
     */
    worker_clr_flags(worker, WORKER_PREP);

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

        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, false);
sleep:
    if (unlikely(need_to_manage_workers(pool)) && manage_workers(worker))
        goto recheck;

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

static int rescuer_thread(void *__wq)
{
    struct workqueue_struct *wq = __wq;
    struct worker *rescuer = wq->rescuer;
    struct list_head *scheduled = &rescuer->scheduled;
    bool is_unbound = wq->flags & WQ_UNBOUND;
    unsigned int cpu;

    set_user_nice(current, RESCUER_NICE_LEVEL);
repeat:
    set_current_state(TASK_INTERRUPTIBLE);

    if (kthread_should_stop()) {
        __set_current_state(TASK_RUNNING);
        return 0;
    }

    /*
     * See whether any cpu is asking for help.  Unbounded
     * workqueues use cpu 0 in mayday_mask for CPU_UNBOUND.
     */
    for_each_mayday_cpu(cpu, wq->mayday_mask) {
        unsigned int tcpu = is_unbound ? WORK_CPU_UNBOUND : cpu;
        struct cpu_workqueue_struct *cwq = get_cwq(tcpu, wq);
        struct worker_pool *pool = cwq->pool;
        struct global_cwq *gcwq = pool->gcwq;
        struct work_struct *work, *n;

        __set_current_state(TASK_RUNNING);
        mayday_clear_cpu(cpu, wq->mayday_mask);

        /* migrate to the target cpu if possible */
        rescuer->pool = pool;
        worker_maybe_bind_and_lock(rescuer);

        /*
         * Slurp in all works issued via this workqueue and
         * process'em.
         */
        BUG_ON(!list_empty(&rescuer->scheduled));
        list_for_each_entry_safe(work, n, &pool->worklist, entry)
            if (get_work_cwq(work) == cwq)
                move_linked_works(work, scheduled, &n);

        process_scheduled_works(rescuer);

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

        spin_unlock_irq(&gcwq->lock);
    }

    schedule();
    goto repeat;
}

struct wq_barrier {
    struct work_struct  work;
    struct completion   done;
};

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

static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
                  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 gcwq->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(&barr->done);

    /*
     * 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(cwq, &barr->work, head,
            work_color_to_flags(WORK_NO_COLOR) | linked);
}

static bool flush_workqueue_prep_cwqs(struct workqueue_struct *wq,
                      int flush_color, int work_color)
{
    bool wait = false;
    unsigned int cpu;

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

    for_each_cwq_cpu(cpu, wq) {
        struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
        struct global_cwq *gcwq = cwq->pool->gcwq;

        spin_lock_irq(&gcwq->lock);

        if (flush_color >= 0) {
            BUG_ON(cwq->flush_color != -1);

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

        if (work_color >= 0) {
            BUG_ON(work_color != work_next_color(cwq->work_color));
            cwq->work_color = work_color;
        }

        spin_unlock_irq(&gcwq->lock);
    }

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

    return wait;
}

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(this_flusher.done),
    };
    int next_color;

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

    mutex_lock(&wq->flush_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.
         */
        BUG_ON(!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 */
            BUG_ON(wq->flush_color != this_flusher.flush_color);

            wq->first_flusher = &this_flusher;

            if (!flush_workqueue_prep_cwqs(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 */
            BUG_ON(wq->flush_color == this_flusher.flush_color);
            list_add_tail(&this_flusher.list, &wq->flusher_queue);
            flush_workqueue_prep_cwqs(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);
    }

    mutex_unlock(&wq->flush_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->flush_mutex);

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

    wq->first_flusher = NULL;

    BUG_ON(!list_empty(&this_flusher.list));
    BUG_ON(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);
        }

        BUG_ON(!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_cwqs(wq, -1, wq->work_color);
        }

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

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

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

        if (flush_workqueue_prep_cwqs(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->flush_mutex);
}
EXPORT_SYMBOL_GPL(flush_workqueue);

void drain_workqueue(struct workqueue_struct *wq)
{
    unsigned int flush_cnt = 0;
    unsigned int cpu;

    /*
     * __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.
     */
    spin_lock(&workqueue_lock);
    if (!wq->nr_drainers++)
        wq->flags |= WQ_DRAINING;
    spin_unlock(&workqueue_lock);
reflush:
    flush_workqueue(wq);

    for_each_cwq_cpu(cpu, wq) {
        struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
        bool drained;

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

        if (drained)
            continue;

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

    spin_lock(&workqueue_lock);
    if (!--wq->nr_drainers)
        wq->flags &= ~WQ_DRAINING;
    spin_unlock(&workqueue_lock);
}
EXPORT_SYMBOL_GPL(drain_workqueue);

static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr)
{
    struct worker *worker = NULL;
    struct global_cwq *gcwq;
    struct cpu_workqueue_struct *cwq;

    might_sleep();
    gcwq = get_work_gcwq(work);
    if (!gcwq)
        return false;

    spin_lock_irq(&gcwq->lock);
    if (!list_empty(&work->entry)) {
        /*
         * See the comment near try_to_grab_pending()->smp_rmb().
         * If it was re-queued to a different gcwq under us, we
         * are not going to wait.
         */
        smp_rmb();
        cwq = get_work_cwq(work);
        if (unlikely(!cwq || gcwq != cwq->pool->gcwq))
            goto already_gone;
    } else {
        worker = find_worker_executing_work(gcwq, work);
        if (!worker)
            goto already_gone;
        cwq = worker->current_cwq;
    }

    insert_wq_barrier(cwq, barr, work, worker);
    spin_unlock_irq(&gcwq->lock);

    /*
     * If @max_active is 1 or rescuer is in use, flushing another work
     * item on the same workqueue may lead to deadlock.  Make sure the
     * flusher is not running on the same workqueue by verifying write
     * access.
     */
    if (cwq->wq->saved_max_active == 1 || cwq->wq->flags & WQ_RESCUER)
        lock_map_acquire(&cwq->wq->lockdep_map);
    else
        lock_map_acquire_read(&cwq->wq->lockdep_map);
    lock_map_release(&cwq->wq->lockdep_map);

    return true;
already_gone:
    spin_unlock_irq(&gcwq->lock);
    return false;
}

bool flush_work(struct work_struct *work)
{
    struct wq_barrier barr;

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

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

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

    do {
        ret = try_to_grab_pending(work, is_dwork, &flags);
        /*
         * If someone else is canceling, wait for the same event it
         * would be waiting for before retrying.
         */
        if (unlikely(ret == -ENOENT))
            flush_work(work);
    } while (unlikely(ret < 0));

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

    flush_work(work);
    clear_work_data(work);
    return ret;
}

bool cancel_work_sync(struct work_struct *work)
{
    return __cancel_work_timer(work, false);
}
EXPORT_SYMBOL_GPL(cancel_work_sync);

bool flush_delayed_work(struct delayed_work *dwork)
{
    local_irq_disable();
    if (del_timer_sync(&dwork->timer))
        __queue_work(dwork->cpu,
                 get_work_cwq(&dwork->work)->wq, &dwork->work);
    local_irq_enable();
    return flush_work(&dwork->work);
}
EXPORT_SYMBOL(flush_delayed_work);

bool cancel_delayed_work(struct delayed_work *dwork)
{
    unsigned long flags;
    int ret;

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

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

    set_work_cpu_and_clear_pending(&dwork->work, work_cpu(&dwork->work));
    local_irq_restore(flags);
    return ret;
}
EXPORT_SYMBOL(cancel_delayed_work);

bool cancel_delayed_work_sync(struct delayed_work *dwork)
{
    return __cancel_work_timer(&dwork->work, true);
}
EXPORT_SYMBOL(cancel_delayed_work_sync);

bool schedule_work_on(int cpu, struct work_struct *work)
{
    return queue_work_on(cpu, system_wq, work);
}
EXPORT_SYMBOL(schedule_work_on);

bool schedule_work(struct work_struct *work)
{
    return queue_work(system_wq, work);
}
EXPORT_SYMBOL(schedule_work);

bool schedule_delayed_work_on(int cpu, struct delayed_work *dwork,
                  unsigned long delay)
{
    return queue_delayed_work_on(cpu, system_wq, dwork, delay);
}
EXPORT_SYMBOL(schedule_delayed_work_on);

bool schedule_delayed_work(struct delayed_work *dwork, unsigned long delay)
{
    return queue_delayed_work(system_wq, dwork, delay);
}
EXPORT_SYMBOL(schedule_delayed_work);

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;
}

void flush_scheduled_work(void)
{
    flush_workqueue(system_wq);
}
EXPORT_SYMBOL(flush_scheduled_work);

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);

int keventd_up(void)
{
    return system_wq != NULL;
}

static int alloc_cwqs(struct workqueue_struct *wq)
{
    /*
     * cwqs are forced aligned according to WORK_STRUCT_FLAG_BITS.
     * Make sure that the alignment isn't lower than that of
     * unsigned long long.
     */
    const size_t size = sizeof(struct cpu_workqueue_struct);
    const size_t align = max_t(size_t, 1 << WORK_STRUCT_FLAG_BITS,
                   __alignof__(unsigned long long));

    if (!(wq->flags & WQ_UNBOUND))
        wq->cpu_wq.pcpu = __alloc_percpu(size, align);
    else {
        void *ptr;

        /*
         * Allocate enough room to align cwq and put an extra
         * pointer at the end pointing back to the originally
         * allocated pointer which will be used for free.
         */
        ptr = kzalloc(size + align + sizeof(void *), GFP_KERNEL);
        if (ptr) {
            wq->cpu_wq.single = PTR_ALIGN(ptr, align);
            *(void **)(wq->cpu_wq.single + 1) = ptr;
        }
    }

    /* just in case, make sure it's actually aligned */
    BUG_ON(!IS_ALIGNED(wq->cpu_wq.v, align));
    return wq->cpu_wq.v ? 0 : -ENOMEM;
}

static void free_cwqs(struct workqueue_struct *wq)
{
    if (!(wq->flags & WQ_UNBOUND))
        free_percpu(wq->cpu_wq.pcpu);
    else if (wq->cpu_wq.single) {
        /* the pointer to free is stored right after the cwq */
        kfree(*(void **)(wq->cpu_wq.single + 1));
    }
}

static int wq_clamp_max_active(int max_active, unsigned int flags,
                   const char *name)
{
    int lim = flags & WQ_UNBOUND ? WQ_UNBOUND_MAX_ACTIVE : WQ_MAX_ACTIVE;

    if (max_active < 1 || max_active > lim)
        pr_warn("workqueue: max_active %d requested for %s is out of range, clamping between %d and %d\n",
            max_active, name, 1, lim);

    return clamp_val(max_active, 1, lim);
}

struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
                           unsigned int flags,
                           int max_active,
                           struct lock_class_key *key,
                           const char *lock_name, ...)
{
    va_list args, args1;
    struct workqueue_struct *wq;
    unsigned int cpu;
    size_t namelen;

    /* determine namelen, allocate wq and format name */
    va_start(args, lock_name);
    va_copy(args1, args);
    namelen = vsnprintf(NULL, 0, fmt, args) + 1;

    wq = kzalloc(sizeof(*wq) + namelen, GFP_KERNEL);
    if (!wq)
        goto err;

    vsnprintf(wq->name, namelen, fmt, args1);
    va_end(args);
    va_end(args1);

    /*
     * Workqueues which may be used during memory reclaim should
     * have a rescuer to guarantee forward progress.
     */
    if (flags & WQ_MEM_RECLAIM)
        flags |= WQ_RESCUER;

    max_active = max_active ?: WQ_DFL_ACTIVE;
    max_active = wq_clamp_max_active(max_active, flags, wq->name);

    /* init wq */
    wq->flags = flags;
    wq->saved_max_active = max_active;
    mutex_init(&wq->flush_mutex);
    atomic_set(&wq->nr_cwqs_to_flush, 0);
    INIT_LIST_HEAD(&wq->flusher_queue);
    INIT_LIST_HEAD(&wq->flusher_overflow);

    lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
    INIT_LIST_HEAD(&wq->list);

    if (alloc_cwqs(wq) < 0)
        goto err;

    for_each_cwq_cpu(cpu, wq) {
        struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
        struct global_cwq *gcwq = get_gcwq(cpu);
        int pool_idx = (bool)(flags & WQ_HIGHPRI);

        BUG_ON((unsigned long)cwq & WORK_STRUCT_FLAG_MASK);
        cwq->pool = &gcwq->pools[pool_idx];
        cwq->wq = wq;
        cwq->flush_color = -1;
        cwq->max_active = max_active;
        INIT_LIST_HEAD(&cwq->delayed_works);
    }

    if (flags & WQ_RESCUER) {
        struct worker *rescuer;

        if (!alloc_mayday_mask(&wq->mayday_mask, GFP_KERNEL))
            goto err;

        wq->rescuer = rescuer = alloc_worker();
        if (!rescuer)
            goto err;

        rescuer->task = kthread_create(rescuer_thread, wq, "%s",
                           wq->name);
        if (IS_ERR(rescuer->task))
            goto err;

        rescuer->task->flags |= PF_THREAD_BOUND;
        wake_up_process(rescuer->task);
    }

    /*
     * workqueue_lock protects global freeze state and workqueues
     * list.  Grab it, set max_active accordingly and add the new
     * workqueue to workqueues list.
     */
    spin_lock(&workqueue_lock);

    if (workqueue_freezing && wq->flags & WQ_FREEZABLE)
        for_each_cwq_cpu(cpu, wq)
            get_cwq(cpu, wq)->max_active = 0;

    list_add(&wq->list, &workqueues);

    spin_unlock(&workqueue_lock);

    return wq;
err:
    if (wq) {
        free_cwqs(wq);
        free_mayday_mask(wq->mayday_mask);
        kfree(wq->rescuer);
        kfree(wq);
    }
    return NULL;
}
EXPORT_SYMBOL_GPL(__alloc_workqueue_key);

void destroy_workqueue(struct workqueue_struct *wq)
{
    unsigned int cpu;

    /* drain it before proceeding with destruction */
    drain_workqueue(wq);

    /*
     * wq list is used to freeze wq, remove from list after
     * flushing is complete in case freeze races us.
     */
    spin_lock(&workqueue_lock);
    list_del(&wq->list);
    spin_unlock(&workqueue_lock);

    /* sanity check */
    for_each_cwq_cpu(cpu, wq) {
        struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
        int i;

        for (i = 0; i < WORK_NR_COLORS; i++)
            BUG_ON(cwq->nr_in_flight[i]);
        BUG_ON(cwq->nr_active);
        BUG_ON(!list_empty(&cwq->delayed_works));
    }

    if (wq->flags & WQ_RESCUER) {
        kthread_stop(wq->rescuer->task);
        free_mayday_mask(wq->mayday_mask);
        kfree(wq->rescuer);
    }

    free_cwqs(wq);
    kfree(wq);
}
EXPORT_SYMBOL_GPL(destroy_workqueue);

static void cwq_set_max_active(struct cpu_workqueue_struct *cwq, int max_active)
{
    cwq->max_active = max_active;

    while (!list_empty(&cwq->delayed_works) &&
           cwq->nr_active < cwq->max_active)
        cwq_activate_first_delayed(cwq);
}

void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
{
    unsigned int cpu;

    max_active = wq_clamp_max_active(max_active, wq->flags, wq->name);

    spin_lock(&workqueue_lock);

    wq->saved_max_active = max_active;

    for_each_cwq_cpu(cpu, wq) {
        struct global_cwq *gcwq = get_gcwq(cpu);

        spin_lock_irq(&gcwq->lock);

        if (!(wq->flags & WQ_FREEZABLE) ||
            !(gcwq->flags & GCWQ_FREEZING))
            cwq_set_max_active(get_cwq(gcwq->cpu, wq), max_active);

        spin_unlock_irq(&gcwq->lock);
    }

    spin_unlock(&workqueue_lock);
}
EXPORT_SYMBOL_GPL(workqueue_set_max_active);

bool workqueue_congested(unsigned int cpu, struct workqueue_struct *wq)
{
    struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);

    return !list_empty(&cwq->delayed_works);
}
EXPORT_SYMBOL_GPL(workqueue_congested);

unsigned int work_cpu(struct work_struct *work)
{
    struct global_cwq *gcwq = get_work_gcwq(work);

    return gcwq ? gcwq->cpu : WORK_CPU_NONE;
}
EXPORT_SYMBOL_GPL(work_cpu);

unsigned int work_busy(struct work_struct *work)
{
    struct global_cwq *gcwq = get_work_gcwq(work);
    unsigned long flags;
    unsigned int ret = 0;

    if (!gcwq)
        return false;

    spin_lock_irqsave(&gcwq->lock, flags);

    if (work_pending(work))
        ret |= WORK_BUSY_PENDING;
    if (find_worker_executing_work(gcwq, work))
        ret |= WORK_BUSY_RUNNING;

    spin_unlock_irqrestore(&gcwq->lock, flags);

    return ret;
}
EXPORT_SYMBOL_GPL(work_busy);

/*
 * CPU hotplug.
 *
 * There are two challenges in supporting CPU hotplug.  Firstly, there
 * are a lot of assumptions on strong associations among work, cwq and
 * gcwq which make migrating pending and scheduled works very
 * difficult to implement without impacting hot paths.  Secondly,
 * gcwqs serve mix of short, long and very long running works making
 * blocked draining impractical.
 *
 * This is solved by allowing a gcwq to be disassociated from the CPU
 * running as an unbound one and allowing it to be reattached later if the
 * cpu comes back online.
 */

/* claim manager positions of all pools */
static void gcwq_claim_assoc_and_lock(struct global_cwq *gcwq)
{
    struct worker_pool *pool;

    for_each_worker_pool(pool, gcwq)
        mutex_lock_nested(&pool->assoc_mutex, pool - gcwq->pools);
    spin_lock_irq(&gcwq->lock);
}

/* release manager positions */
static void gcwq_release_assoc_and_unlock(struct global_cwq *gcwq)
{
    struct worker_pool *pool;

    spin_unlock_irq(&gcwq->lock);
    for_each_worker_pool(pool, gcwq)
        mutex_unlock(&pool->assoc_mutex);
}

static void gcwq_unbind_fn(struct work_struct *work)
{
    struct global_cwq *gcwq = get_gcwq(smp_processor_id());
    struct worker_pool *pool;
    struct worker *worker;
    struct hlist_node *pos;
    int i;

    BUG_ON(gcwq->cpu != smp_processor_id());

    gcwq_claim_assoc_and_lock(gcwq);

    /*
     * We've claimed all manager positions.  Make all workers unbound
     * and set DISASSOCIATED.  Before this, all workers except for the
     * ones which are still executing works from before the last CPU
     * down must be on the cpu.  After this, they may become diasporas.
     */
    for_each_worker_pool(pool, gcwq)
        list_for_each_entry(worker, &pool->idle_list, entry)
            worker->flags |= WORKER_UNBOUND;

    for_each_busy_worker(worker, i, pos, gcwq)
        worker->flags |= WORKER_UNBOUND;

    gcwq->flags |= GCWQ_DISASSOCIATED;

    gcwq_release_assoc_and_unlock(gcwq);

    /*
     * Call schedule() so that we cross rq->lock and thus can guarantee
     * sched callbacks see the %WORKER_UNBOUND flag.  This is necessary
     * as scheduler callbacks may be invoked from other cpus.
     */
    schedule();

    /*
     * Sched callbacks are disabled now.  Zap nr_running.  After this,
     * nr_running stays zero and need_more_worker() and keep_working()
     * are always true as long as the worklist is not empty.  @gcwq now
     * behaves as unbound (in terms of concurrency management) gcwq
     * which is served by workers tied to the CPU.
     *
     * On return from this function, the current worker would trigger
     * unbound chain execution of pending work items if other workers
     * didn't already.
     */
    for_each_worker_pool(pool, gcwq)
        atomic_set(get_pool_nr_running(pool), 0);
}

/*
 * Workqueues should be brought up before normal priority CPU notifiers.
 * This will be registered high priority CPU notifier.
 */
static int __cpuinit workqueue_cpu_up_callback(struct notifier_block *nfb,
                           unsigned long action,
                           void *hcpu)
{
    unsigned int cpu = (unsigned long)hcpu;
    struct global_cwq *gcwq = get_gcwq(cpu);
    struct worker_pool *pool;

    switch (action & ~CPU_TASKS_FROZEN) {
    case CPU_UP_PREPARE:
        for_each_worker_pool(pool, gcwq) {
            struct worker *worker;

            if (pool->nr_workers)
                continue;

            worker = create_worker(pool);
            if (!worker)
                return NOTIFY_BAD;

            spin_lock_irq(&gcwq->lock);
            start_worker(worker);
            spin_unlock_irq(&gcwq->lock);
        }
        break;

    case CPU_DOWN_FAILED:
    case CPU_ONLINE:
        gcwq_claim_assoc_and_lock(gcwq);
        gcwq->flags &= ~GCWQ_DISASSOCIATED;
        rebind_workers(gcwq);
        gcwq_release_assoc_and_unlock(gcwq);
        break;
    }
    return NOTIFY_OK;
}

/*
 * Workqueues should be brought down after normal priority CPU notifiers.
 * This will be registered as low priority CPU notifier.
 */
static int __cpuinit workqueue_cpu_down_callback(struct notifier_block *nfb,
                         unsigned long action,
                         void *hcpu)
{
    unsigned int cpu = (unsigned long)hcpu;
    struct work_struct unbind_work;

    switch (action & ~CPU_TASKS_FROZEN) {
    case CPU_DOWN_PREPARE:
        /* unbinding should happen on the local CPU */
        INIT_WORK_ONSTACK(&unbind_work, gcwq_unbind_fn);
        queue_work_on(cpu, system_highpri_wq, &unbind_work);
        flush_work(&unbind_work);
        break;
    }
    return NOTIFY_OK;
}

#ifdef CONFIG_SMP

struct work_for_cpu {
    struct work_struct work;
    long (*fn)(void *);
    void *arg;
    long ret;
};

static void work_for_cpu_fn(struct work_struct *work)
{
    struct work_for_cpu *wfc = container_of(work, struct work_for_cpu, work);

    wfc->ret = wfc->fn(wfc->arg);
}

long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg)
{
    struct work_for_cpu wfc = { .fn = fn, .arg = arg };

    INIT_WORK_ONSTACK(&wfc.work, work_for_cpu_fn);
    schedule_work_on(cpu, &wfc.work);
    flush_work(&wfc.work);
    return wfc.ret;
}
EXPORT_SYMBOL_GPL(work_on_cpu);
#endif /* CONFIG_SMP */

#ifdef CONFIG_FREEZER

void freeze_workqueues_begin(void)
{
    unsigned int cpu;

    spin_lock(&workqueue_lock);

    BUG_ON(workqueue_freezing);
    workqueue_freezing = true;

    for_each_gcwq_cpu(cpu) {
        struct global_cwq *gcwq = get_gcwq(cpu);
        struct workqueue_struct *wq;

        spin_lock_irq(&gcwq->lock);

        BUG_ON(gcwq->flags & GCWQ_FREEZING);
        gcwq->flags |= GCWQ_FREEZING;

        list_for_each_entry(wq, &workqueues, list) {
            struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);

            if (cwq && wq->flags & WQ_FREEZABLE)
                cwq->max_active = 0;
        }

        spin_unlock_irq(&gcwq->lock);
    }

    spin_unlock(&workqueue_lock);
}

bool freeze_workqueues_busy(void)
{
    unsigned int cpu;
    bool busy = false;

    spin_lock(&workqueue_lock);

    BUG_ON(!workqueue_freezing);

    for_each_gcwq_cpu(cpu) {
        struct workqueue_struct *wq;
        /*
         * nr_active is monotonically decreasing.  It's safe
         * to peek without lock.
         */
        list_for_each_entry(wq, &workqueues, list) {
            struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);

            if (!cwq || !(wq->flags & WQ_FREEZABLE))
                continue;

            BUG_ON(cwq->nr_active < 0);
            if (cwq->nr_active) {
                busy = true;
                goto out_unlock;
            }
        }
    }
out_unlock:
    spin_unlock(&workqueue_lock);
    return busy;
}

void thaw_workqueues(void)
{
    unsigned int cpu;

    spin_lock(&workqueue_lock);

    if (!workqueue_freezing)
        goto out_unlock;

    for_each_gcwq_cpu(cpu) {
        struct global_cwq *gcwq = get_gcwq(cpu);
        struct worker_pool *pool;
        struct workqueue_struct *wq;

        spin_lock_irq(&gcwq->lock);

        BUG_ON(!(gcwq->flags & GCWQ_FREEZING));
        gcwq->flags &= ~GCWQ_FREEZING;

        list_for_each_entry(wq, &workqueues, list) {
            struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);

            if (!cwq || !(wq->flags & WQ_FREEZABLE))
                continue;

            /* restore max_active and repopulate worklist */
            cwq_set_max_active(cwq, wq->saved_max_active);
        }

        for_each_worker_pool(pool, gcwq)
            wake_up_worker(pool);

        spin_unlock_irq(&gcwq->lock);
    }

    workqueue_freezing = false;
out_unlock:
    spin_unlock(&workqueue_lock);
}
#endif /* CONFIG_FREEZER */

static int __init init_workqueues(void)
{
    unsigned int cpu;
    int i;

    /* make sure we have enough bits for OFFQ CPU number */
    BUILD_BUG_ON((1LU << (BITS_PER_LONG - WORK_OFFQ_CPU_SHIFT)) <
             WORK_CPU_LAST);

    cpu_notifier(workqueue_cpu_up_callback, CPU_PRI_WORKQUEUE_UP);
    hotcpu_notifier(workqueue_cpu_down_callback, CPU_PRI_WORKQUEUE_DOWN);

    /* initialize gcwqs */
    for_each_gcwq_cpu(cpu) {
        struct global_cwq *gcwq = get_gcwq(cpu);
        struct worker_pool *pool;

        spin_lock_init(&gcwq->lock);
        gcwq->cpu = cpu;
        gcwq->flags |= GCWQ_DISASSOCIATED;

        for (i = 0; i < BUSY_WORKER_HASH_SIZE; i++)
            INIT_HLIST_HEAD(&gcwq->busy_hash[i]);

        for_each_worker_pool(pool, gcwq) {
            pool->gcwq = gcwq;
            INIT_LIST_HEAD(&pool->worklist);
            INIT_LIST_HEAD(&pool->idle_list);

            init_timer_deferrable(&pool->idle_timer);
            pool->idle_timer.function = idle_worker_timeout;
            pool->idle_timer.data = (unsigned long)pool;

            setup_timer(&pool->mayday_timer, gcwq_mayday_timeout,
                    (unsigned long)pool);

            mutex_init(&pool->assoc_mutex);
            ida_init(&pool->worker_ida);
        }
    }

    /* create the initial worker */
    for_each_online_gcwq_cpu(cpu) {
        struct global_cwq *gcwq = get_gcwq(cpu);
        struct worker_pool *pool;

        if (cpu != WORK_CPU_UNBOUND)
            gcwq->flags &= ~GCWQ_DISASSOCIATED;

        for_each_worker_pool(pool, gcwq) {
            struct worker *worker;

            worker = create_worker(pool);
            BUG_ON(!worker);
            spin_lock_irq(&gcwq->lock);
            start_worker(worker);
            spin_unlock_irq(&gcwq->lock);
        }
    }

    system_wq = alloc_workqueue("events", 0, 0);
    system_highpri_wq = alloc_workqueue("events_highpri", WQ_HIGHPRI, 0);
    system_long_wq = alloc_workqueue("events_long", 0, 0);
    system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND,
                        WQ_UNBOUND_MAX_ACTIVE);
    system_freezable_wq = alloc_workqueue("events_freezable",
                          WQ_FREEZABLE, 0);
    BUG_ON(!system_wq || !system_highpri_wq || !system_long_wq ||
           !system_unbound_wq || !system_freezable_wq);
    return 0;
}
early_initcall(init_workqueues);