workqueue: fix race condition in unbound workqueue free path

[karo-tx-linux.git] / kernel / workqueue.c

/*
 * kernel/workqueue.c - generic async execution with shared worker pool
 *
 * Copyright (C) 2002           Ingo Molnar
 *
 *   Derived from the taskqueue/keventd code by:
 *     David Woodhouse <dwmw2@infradead.org>
 *     Andrew Morton
 *     Kai Petzke <wpp@marie.physik.tu-berlin.de>
 *     Theodore Ts'o <tytso@mit.edu>
 *
 * Made to use alloc_percpu by Christoph Lameter.
 *
 * Copyright (C) 2010           SUSE Linux Products GmbH
 * Copyright (C) 2010           Tejun Heo <tj@kernel.org>
 *
 * This is the generic async execution mechanism.  Work items as are
 * executed in process context.  The worker pool is shared and
 * automatically managed.  There 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 <linux/jhash.h>
#include <linux/hashtable.h>
#include <linux/rculist.h>

#include "workqueue_internal.h"

enum {
        /*
         * worker_pool flags
         *
         * A bound pool is either associated or disassociated with its CPU.
         * While associated (!DISASSOCIATED), all workers are bound to the
         * CPU and none has %WORKER_UNBOUND set and concurrency management
         * is in effect.
         *
         * While DISASSOCIATED, the cpu may be offline and all workers have
         * %WORKER_UNBOUND set and concurrency management disabled, and may
         * be executing on any CPU.  The pool behaves as an unbound one.
         *
         * Note that DISASSOCIATED should be flipped only while holding
         * manager_mutex to avoid changing binding state while
         * create_worker() is in progress.
         */
        POOL_MANAGE_WORKERS     = 1 << 0,       /* need to manage workers */
        POOL_DISASSOCIATED      = 1 << 2,       /* cpu can't serve workers */
        POOL_FREEZING           = 1 << 3,       /* freeze in progress */

        /* 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_REBOUND          = 1 << 8,       /* worker was rebound */

        WORKER_NOT_RUNNING      = WORKER_PREP | WORKER_CPU_INTENSIVE |
                                  WORKER_UNBOUND | WORKER_REBOUND,

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

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

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

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

        /*
         * Rescue workers are used only on emergencies and shared by
         * all cpus.  Give -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: pool->lock protected.  Access with pool->lock held.
 *
 * X: During normal operation, modification requires pool->lock and should
 *    be done only from local cpu.  Either disabling preemption on local
 *    cpu or grabbing pool->lock is enough for read access.  If
 *    POOL_DISASSOCIATED is set, it's identical to L.
 *
 * MG: pool->manager_mutex and pool->lock protected.  Writes require both
 *     locks.  Reads can happen under either lock.
 *
 * PL: wq_pool_mutex protected.
 *
 * PR: wq_pool_mutex protected for writes.  Sched-RCU protected for reads.
 *
 * WQ: wq->mutex protected.
 *
 * WR: wq->mutex protected for writes.  Sched-RCU protected for reads.
 *
 * MD: wq_mayday_lock protected.
 */

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

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

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

        /* see manage_workers() for details on the two manager mutexes */
        struct mutex            manager_arb;    /* manager arbitration */
        struct mutex            manager_mutex;  /* manager exclusion */
        struct idr              worker_idr;     /* MG: worker IDs and iteration */

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

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

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

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

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

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

struct wq_device;

/*
 * The externally visible workqueue.  It relays the issued work items to
 * the appropriate worker_pool through its pool_workqueues.
 */
struct workqueue_struct {
        unsigned int            flags;          /* WQ: WQ_* flags */
        struct pool_workqueue __percpu *cpu_pwqs; /* I: per-cpu pwq's */
        struct list_head        pwqs;           /* WR: all pwqs of this wq */
        struct list_head        list;           /* PL: list of all workqueues */

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

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

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

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

static struct kmem_cache *pwq_cache;

static DEFINE_MUTEX(wq_pool_mutex);     /* protects pools and workqueues list */
static DEFINE_SPINLOCK(wq_mayday_lock); /* protects wq->maydays list */

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

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

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

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

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

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);

static int worker_thread(void *__worker);
static void copy_workqueue_attrs(struct workqueue_attrs *to,
                                 const struct workqueue_attrs *from);

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

#define assert_rcu_or_pool_mutex()                                      \
        rcu_lockdep_assert(rcu_read_lock_sched_held() ||                \
                           lockdep_is_held(&wq_pool_mutex),             \
                           "sched RCU or wq_pool_mutex should be held")

#define assert_rcu_or_wq_mutex(wq)                                      \
        rcu_lockdep_assert(rcu_read_lock_sched_held() ||                \
                           lockdep_is_held(&wq->mutex),                 \
                           "sched RCU or wq->mutex should be held")

#ifdef CONFIG_LOCKDEP
#define assert_manager_or_pool_lock(pool)                               \
        WARN_ONCE(debug_locks &&                                        \
                  !lockdep_is_held(&(pool)->manager_mutex) &&           \
                  !lockdep_is_held(&(pool)->lock),                      \
                  "pool->manager_mutex or ->lock should be held")
#else
#define assert_manager_or_pool_lock(pool)       do { } while (0)
#endif

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

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

/**
 * for_each_pool_worker - iterate through all workers of a worker_pool
 * @worker: iteration cursor
 * @wi: integer used for iteration
 * @pool: worker_pool to iterate workers of
 *
 * This must be called with either @pool->manager_mutex or ->lock held.
 *
 * The if/else clause exists only for the lockdep assertion and can be
 * ignored.
 */
#define for_each_pool_worker(worker, wi, pool)                          \
        idr_for_each_entry(&(pool)->worker_idr, (worker), (wi))         \
                if (({ assert_manager_or_pool_lock((pool)); false; })) { } \
                else

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

#ifdef CONFIG_DEBUG_OBJECTS_WORK

static struct debug_obj_descr work_debug_descr;

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

/*
 * 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

/* allocate ID and assign it to @pool */
static int worker_pool_assign_id(struct worker_pool *pool)
{
        int ret;

        lockdep_assert_held(&wq_pool_mutex);

        do {
                if (!idr_pre_get(&worker_pool_idr, GFP_KERNEL))
                        return -ENOMEM;
                ret = idr_get_new(&worker_pool_idr, pool, &pool->id);
        } while (ret == -EAGAIN);

        return ret;
}

/**
 * first_pwq - return the first pool_workqueue of the specified workqueue
 * @wq: the target workqueue
 *
 * This must be called either with wq->mutex held or sched RCU read locked.
 * If the pwq needs to be used beyond the locking in effect, the caller is
 * responsible for guaranteeing that the pwq stays online.
 */
static struct pool_workqueue *first_pwq(struct workqueue_struct *wq)
{
        assert_rcu_or_wq_mutex(wq);
        return list_first_or_null_rcu(&wq->pwqs, struct pool_workqueue,
                                      pwqs_node);
}

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

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

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

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

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

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

static void set_work_pool_and_clear_pending(struct work_struct *work,
                                            int pool_id)
{
        /*
         * The following wmb is paired with the implied mb in
         * test_and_set_bit(PENDING) and ensures all updates to @work made
         * here are visible to and precede any updates by the next PENDING
         * owner.
         */
        smp_wmb();
        set_work_data(work, (unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT, 0);
}

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

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

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

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

        assert_rcu_or_pool_mutex();

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

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

        return idr_find(&worker_pool_idr, pool_id);
}

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

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

        return data >> WORK_OFFQ_POOL_SHIFT;
}

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

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

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

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

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

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

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

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

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

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

/* Do 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 = mutex_is_locked(&pool->manager_arb);
        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);
}

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

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

/**
 * wq_worker_waking_up - a worker is waking up
 * @task: task waking up
 * @cpu: CPU @task is waking up to
 *
 * This function is called during try_to_wake_up() when a worker is
 * being awoken.
 *
 * CONTEXT:
 * spin_lock_irq(rq->lock)
 */
void wq_worker_waking_up(struct task_struct *task, int cpu)
{
        struct worker *worker = kthread_data(task);

        if (!(worker->flags & WORKER_NOT_RUNNING)) {
                WARN_ON_ONCE(worker->pool->cpu != cpu);
                atomic_inc(&worker->pool->nr_running);
        }
}

/**
 * wq_worker_sleeping - a worker is going to sleep
 * @task: task going to sleep
 * @cpu: CPU in question, must be the current CPU number
 *
 * This function is called during schedule() when a busy worker is
 * going to sleep.  Worker on the same cpu can be woken up by
 * returning pointer to its task.
 *
 * CONTEXT:
 * spin_lock_irq(rq->lock)
 *
 * RETURNS:
 * Worker task on @cpu to wake up, %NULL if none.
 */
struct task_struct *wq_worker_sleeping(struct task_struct *task, int cpu)
{
        struct worker *worker = kthread_data(task), *to_wakeup = NULL;
        struct worker_pool *pool;

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

        pool = worker->pool;

        /* this can only happen on the local cpu */
        if (WARN_ON_ONCE(cpu != raw_smp_processor_id()))
                return NULL;

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

/**
 * worker_set_flags - set worker flags and adjust nr_running accordingly
 * @worker: self
 * @flags: flags to set
 * @wakeup: wakeup an idle worker if necessary
 *
 * Set @flags in @worker->flags and adjust nr_running accordingly.  If
 * nr_running becomes zero and @wakeup is %true, an idle worker is
 * woken up.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock)
 */
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)) {
                if (wakeup) {
                        if (atomic_dec_and_test(&pool->nr_running) &&
                            !list_empty(&pool->worklist))
                                wake_up_worker(pool);
                } else
                        atomic_dec(&pool->nr_running);
        }

        worker->flags |= flags;
}

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

        WARN_ON_ONCE(worker->task != current);

        worker->flags &= ~flags;

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

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

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

        return NULL;
}

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

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

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

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

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

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

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

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

        pwq_activate_delayed_work(work);
}

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

        pwq->nr_in_flight[color]--;

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

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

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

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

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

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

        local_irq_save(*flags);

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        /*
         * While a work item is PENDING && off queue, a task trying to
         * steal the PENDING will busy-loop waiting for it to either get
         * queued or lose PENDING.  Grabbing PENDING and queueing should
         * happen with IRQ disabled.
         */
        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;
retry:
        /* pwq which will be used unless @work is executing elsewhere */
        if (!(wq->flags & WQ_UNBOUND)) {
                if (cpu == WORK_CPU_UNBOUND)
                        cpu = raw_smp_processor_id();
                pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
        } else {
                pwq = first_pwq(wq);
        }

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

                spin_lock(&last_pool->lock);

                worker = find_worker_executing_work(last_pool, work);

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

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

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

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

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

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

        insert_work(pwq, work, worklist, work_flags);

        spin_unlock(&pwq->pool->lock);
}

/**
 * queue_work_on - queue work on specific cpu
 * @cpu: CPU number to execute work on
 * @wq: workqueue to use
 * @work: work to queue
 *
 * Returns %false if @work was already on a queue, %true otherwise.
 *
 * We queue the work to a specific CPU, the caller must ensure it
 * can't go away.
 */
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);

void delayed_work_timer_fn(unsigned long __data)
{
        struct delayed_work *dwork = (struct delayed_work *)__data;

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

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

        WARN_ON_ONCE(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);

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

/**
 * worker_maybe_bind_and_lock - try to bind %current to worker_pool and lock it
 * @pool: target worker_pool
 *
 * Bind %current to the cpu of @pool if it is associated and lock @pool.
 *
 * Works which are scheduled while the cpu is online must at least be
 * scheduled to a worker which is bound to the cpu so that if they are
 * flushed from cpu callbacks while cpu is going down, they are
 * guaranteed to execute on the cpu.
 *
 * This function is to be used by unbound workers and rescuers to bind
 * themselves to the target cpu and may race with cpu going down or
 * coming online.  kthread_bind() can't be used because it may put the
 * worker to already dead cpu and set_cpus_allowed_ptr() can't be used
 * verbatim as it's best effort and blocking and pool may be
 * [dis]associated in the meantime.
 *
 * This function tries set_cpus_allowed() and locks pool and verifies the
 * binding against %POOL_DISASSOCIATED which is set during
 * %CPU_DOWN_PREPARE and cleared during %CPU_ONLINE, so if the worker
 * enters idle state or fetches works without dropping lock, it can
 * guarantee the scheduling requirement described in the first paragraph.
 *
 * CONTEXT:
 * Might sleep.  Called without any lock but returns with pool->lock
 * held.
 *
 * RETURNS:
 * %true if the associated pool is online (@worker is successfully
 * bound), %false if offline.
 */
static bool worker_maybe_bind_and_lock(struct worker_pool *pool)
__acquires(&pool->lock)
{
        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 POOL_DISASSOCIATED.
                 */
                if (!(pool->flags & POOL_DISASSOCIATED))
                        set_cpus_allowed_ptr(current, pool->attrs->cpumask);

                spin_lock_irq(&pool->lock);
                if (pool->flags & POOL_DISASSOCIATED)
                        return false;
                if (task_cpu(current) == pool->cpu &&
                    cpumask_equal(&current->cpus_allowed, pool->attrs->cpumask))
                        return true;
                spin_unlock_irq(&pool->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();
        }
}

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);
                /* on creation a worker is in !idle && prep state */
                worker->flags = WORKER_PREP;
        }
        return worker;
}

/**
 * create_worker - create a new workqueue worker
 * @pool: pool the new worker will belong to
 *
 * Create a new worker which is bound to @pool.  The returned worker
 * can be started by calling start_worker() or destroyed using
 * destroy_worker().
 *
 * CONTEXT:
 * Might sleep.  Does GFP_KERNEL allocations.
 *
 * RETURNS:
 * Pointer to the newly created worker.
 */
static struct worker *create_worker(struct worker_pool *pool)
{
        const char *pri = pool->attrs->nice < 0  ? "H" : "";
        struct worker *worker = NULL;
        int id = -1;

        lockdep_assert_held(&pool->manager_mutex);

        /*
         * ID is needed to determine kthread name.  Allocate ID first
         * without installing the pointer.
         */
        idr_preload(GFP_KERNEL);
        spin_lock_irq(&pool->lock);

        id = idr_alloc(&pool->worker_idr, NULL, 0, 0, GFP_NOWAIT);

        spin_unlock_irq(&pool->lock);
        idr_preload_end();
        if (id < 0)
                goto fail;

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

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

        if (pool->cpu >= 0)
                worker->task = kthread_create_on_node(worker_thread,
                                        worker, cpu_to_node(pool->cpu),
                                        "kworker/%d:%d%s", pool->cpu, id, pri);
        else
                worker->task = kthread_create(worker_thread, worker,
                                              "kworker/u%d:%d%s",
                                              pool->id, id, pri);
        if (IS_ERR(worker->task))
                goto fail;

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

        /* prevent userland from meddling with cpumask of workqueue workers */
        worker->task->flags |= PF_NO_SETAFFINITY;

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

        /* successful, commit the pointer to idr */
        spin_lock_irq(&pool->lock);
        idr_replace(&pool->worker_idr, worker, worker->id);
        spin_unlock_irq(&pool->lock);

        return worker;

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

/**
 * start_worker - start a newly created worker
 * @worker: worker to start
 *
 * Make the pool aware of @worker and start it.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock).
 */
static void start_worker(struct worker *worker)
{
        worker->flags |= WORKER_STARTED;
        worker->pool->nr_workers++;
        worker_enter_idle(worker);
        wake_up_process(worker->task);
}

/**
 * create_and_start_worker - create and start a worker for a pool
 * @pool: the target pool
 *
 * Grab the managership of @pool and create and start a new worker for it.
 */
static int create_and_start_worker(struct worker_pool *pool)
{
        struct worker *worker;

        mutex_lock(&pool->manager_mutex);

        worker = create_worker(pool);
        if (worker) {
                spin_lock_irq(&pool->lock);
                start_worker(worker);
                spin_unlock_irq(&pool->lock);
        }

        mutex_unlock(&pool->manager_mutex);

        return worker ? 0 : -ENOMEM;
}

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

        lockdep_assert_held(&pool->manager_mutex);
        lockdep_assert_held(&pool->lock);

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

        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;

        idr_remove(&pool->worker_idr, worker->id);

        spin_unlock_irq(&pool->lock);

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

        spin_lock_irq(&pool->lock);
}

static void idle_worker_timeout(unsigned long __pool)
{
        struct worker_pool *pool = (void *)__pool;

        spin_lock_irq(&pool->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(&pool->lock);
}

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

        lockdep_assert_held(&wq_mayday_lock);

        if (!wq->rescuer)
                return;

        /* mayday mayday mayday */
        if (list_empty(&pwq->mayday_node)) {
                list_add_tail(&pwq->mayday_node, &wq->maydays);
                wake_up_process(wq->rescuer->task);
        }
}

static void pool_mayday_timeout(unsigned long __pool)
{
        struct worker_pool *pool = (void *)__pool;
        struct work_struct *work;

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

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

/**
 * maybe_create_worker - create a new worker if necessary
 * @pool: pool to create a new worker for
 *
 * Create a new worker for @pool if necessary.  @pool is guaranteed to
 * have at least one idle worker on return from this function.  If
 * creating a new worker takes longer than MAYDAY_INTERVAL, mayday is
 * sent to all rescuers with works scheduled on @pool to resolve
 * possible allocation deadlock.
 *
 * On return, need_to_create_worker() is guaranteed to be %false and
 * may_start_working() %true.
 *
 * LOCKING:
 * spin_lock_irq(pool->lock) which may be released and regrabbed
 * multiple times.  Does GFP_KERNEL allocations.  Called only from
 * manager.
 *
 * RETURNS:
 * %false if no action was taken and pool->lock stayed locked, %true
 * otherwise.
 */
static bool maybe_create_worker(struct worker_pool *pool)
__releases(&pool->lock)
__acquires(&pool->lock)
{
        if (!need_to_create_worker(pool))
                return false;
restart:
        spin_unlock_irq(&pool->lock);

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

        while (true) {
                struct worker *worker;

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

/**
 * maybe_destroy_worker - destroy workers which have been idle for a while
 * @pool: pool to destroy workers for
 *
 * Destroy @pool workers which have been idle for longer than
 * IDLE_WORKER_TIMEOUT.
 *
 * LOCKING:
 * spin_lock_irq(pool->lock) which may be released and regrabbed
 * multiple times.  Called only from manager.
 *
 * RETURNS:
 * %false if no action was taken and pool->lock stayed locked, %true
 * otherwise.
 */
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;
}

/**
 * manage_workers - manage worker pool
 * @worker: self
 *
 * Assume the manager role and manage the worker pool @worker belongs
 * to.  At any given time, there can be only zero or one manager per
 * pool.  The exclusion is handled automatically by this function.
 *
 * The caller can safely start processing works on false return.  On
 * true return, it's guaranteed that need_to_create_worker() is false
 * and may_start_working() is true.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock) which may be released and regrabbed
 * multiple times.  Does GFP_KERNEL allocations.
 *
 * RETURNS:
 * spin_lock_irq(pool->lock) which may be released and regrabbed
 * multiple times.  Does GFP_KERNEL allocations.
 */
static bool manage_workers(struct worker *worker)
{
        struct worker_pool *pool = worker->pool;
        bool ret = false;

        /*
         * Managership is governed by two mutexes - manager_arb and
         * manager_mutex.  manager_arb handles arbitration of manager role.
         * Anyone who successfully grabs manager_arb wins the arbitration
         * and becomes the manager.  mutex_trylock() on pool->manager_arb
         * failure while holding pool->lock reliably indicates that someone
         * else is managing the pool and the worker which failed trylock
         * can proceed to executing work items.  This means that anyone
         * grabbing manager_arb is responsible for actually performing
         * manager duties.  If manager_arb is grabbed and released without
         * actual management, the pool may stall indefinitely.
         *
         * manager_mutex is used for exclusion of actual management
         * operations.  The holder of manager_mutex can be sure that none
         * of management operations, including creation and destruction of
         * workers, won't take place until the mutex is released.  Because
         * manager_mutex doesn't interfere with manager role arbitration,
         * it is guaranteed that the pool's management, while may be
         * delayed, won't be disturbed by someone else grabbing
         * manager_mutex.
         */
        if (!mutex_trylock(&pool->manager_arb))
                return ret;

        /*
         * With manager arbitration won, manager_mutex would be free in
         * most cases.  trylock first without dropping @pool->lock.
         */
        if (unlikely(!mutex_trylock(&pool->manager_mutex))) {
                spin_unlock_irq(&pool->lock);
                mutex_lock(&pool->manager_mutex);
                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);

        mutex_unlock(&pool->manager_mutex);
        mutex_unlock(&pool->manager_arb);
        return ret;
}

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

        lockdep_copy_map(&lockdep_map, &work->lockdep_map);
#endif
        /*
         * Ensure we're on the correct CPU.  DISASSOCIATED test is
         * necessary to avoid spurious warnings from rescuers servicing the
         * unbound or a disassociated pool.
         */
        WARN_ON_ONCE(!(worker->flags & WORKER_UNBOUND) &&
                     !(pool->flags & POOL_DISASSOCIATED) &&
                     raw_smp_processor_id() != pool->cpu);

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

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

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

        spin_unlock_irq(&pool->lock);

        lock_map_acquire_read(&pwq->wq->lockdep_map);
        lock_map_acquire(&lockdep_map);
        trace_workqueue_execute_start(work);
        worker->current_func(work);
        /*
         * While we must be careful to not use "work" after this, the trace
         * point will only record its address.
         */
        trace_workqueue_execute_end(work);
        lock_map_release(&lockdep_map);
        lock_map_release(&pwq->wq->lockdep_map);

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

        spin_lock_irq(&pool->lock);

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

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

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

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

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

        /* am I supposed to die? */
        if (unlikely(worker->flags & WORKER_DIE)) {
                spin_unlock_irq(&pool->lock);
                WARN_ON_ONCE(!list_empty(&worker->entry));
                worker->task->flags &= ~PF_WQ_WORKER;
                return 0;
        }

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

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

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

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

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

                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;

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

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

        set_user_nice(current, RESCUER_NICE_LEVEL);

        /*
         * Mark rescuer as worker too.  As WORKER_PREP is never cleared, it
         * doesn't participate in concurrency management.
         */
        rescuer->task->flags |= PF_WQ_WORKER;
repeat:
        set_current_state(TASK_INTERRUPTIBLE);

        if (kthread_should_stop()) {
                __set_current_state(TASK_RUNNING);
                rescuer->task->flags &= ~PF_WQ_WORKER;
                return 0;
        }

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

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

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

                spin_unlock_irq(&wq_mayday_lock);

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

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

                process_scheduled_works(rescuer);

                /*
                 * Leave this pool.  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);

                rescuer->pool = NULL;
                spin_unlock(&pool->lock);
                spin_lock(&wq_mayday_lock);
        }

        spin_unlock_irq(&wq_mayday_lock);

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

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

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

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

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

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

                spin_lock_irq(&pool->lock);

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

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

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

                spin_unlock_irq(&pool->lock);
        }

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

        return wait;
}

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

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

        mutex_lock(&wq->mutex);

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

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

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

                        wq->first_flusher = &this_flusher;

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

        mutex_unlock(&wq->mutex);

        wait_for_completion(&this_flusher.done);

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

        mutex_lock(&wq->mutex);

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

        wq->first_flusher = NULL;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        mutex_lock(&wq->mutex);

        for_each_pwq(pwq, wq) {
                bool drained;

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

                if (drained)
                        continue;

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

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

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

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

        might_sleep();

        local_irq_disable();
        pool = get_work_pool(work);
        if (!pool) {
                local_irq_enable();
                return false;
        }

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

        insert_wq_barrier(pwq, barr, work, worker);
        spin_unlock_irq(&pool->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 (pwq->wq->saved_max_active == 1 || pwq->wq->rescuer)
                lock_map_acquire(&pwq->wq->lockdep_map);
        else
                lock_map_acquire_read(&pwq->wq->lockdep_map);
        lock_map_release(&pwq->wq->lockdep_map);

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

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

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

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

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

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

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

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

        get_online_cpus();

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

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

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

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

/**
 * flush_scheduled_work - ensure that any scheduled work has run to completion.
 *
 * Forces execution of the kernel-global workqueue and blocks until its
 * completion.
 *
 * Think twice before calling this function!  It's very easy to get into
 * trouble if you don't take great care.  Either of the following situations
 * will lead to deadlock:
 *
 *      One of the work items currently on the workqueue needs to acquire
 *      a lock held by your code or its caller.
 *
 *      Your code is running in the context of a work routine.
 *
 * They will be detected by lockdep when they occur, but the first might not
 * occur very often.  It depends on what work items are on the workqueue and
 * what locks they need, which you have no control over.
 *
 * In most situations flushing the entire workqueue is overkill; you merely
 * need to know that a particular work item isn't queued and isn't running.
 * In such cases you should use cancel_delayed_work_sync() or
 * cancel_work_sync() instead.
 */
void flush_scheduled_work(void)
{
        flush_workqueue(system_wq);
}
EXPORT_SYMBOL(flush_scheduled_work);

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

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

        return 1;
}
EXPORT_SYMBOL_GPL(execute_in_process_context);

#ifdef CONFIG_SYSFS
/*
 * Workqueues with WQ_SYSFS flag set is visible to userland via
 * /sys/bus/workqueue/devices/WQ_NAME.  All visible workqueues have the
 * following attributes.
 *
 *  per_cpu     RO bool : whether the workqueue is per-cpu or unbound
 *  max_active  RW int  : maximum number of in-flight work items
 *
 * Unbound workqueues have the following extra attributes.
 *
 *  id          RO int  : the associated pool ID
 *  nice        RW int  : nice value of the workers
 *  cpumask     RW mask : bitmask of allowed CPUs for the workers
 */
struct wq_device {
        struct workqueue_struct         *wq;
        struct device                   dev;
};

static struct workqueue_struct *dev_to_wq(struct device *dev)
{
        struct wq_device *wq_dev = container_of(dev, struct wq_device, dev);

        return wq_dev->wq;
}

static ssize_t wq_per_cpu_show(struct device *dev,
                               struct device_attribute *attr, char *buf)
{
        struct workqueue_struct *wq = dev_to_wq(dev);

        return scnprintf(buf, PAGE_SIZE, "%d\n", (bool)!(wq->flags & WQ_UNBOUND));
}

static ssize_t wq_max_active_show(struct device *dev,
                                  struct device_attribute *attr, char *buf)
{
        struct workqueue_struct *wq = dev_to_wq(dev);

        return scnprintf(buf, PAGE_SIZE, "%d\n", wq->saved_max_active);
}

static ssize_t wq_max_active_store(struct device *dev,
                                   struct device_attribute *attr,
                                   const char *buf, size_t count)
{
        struct workqueue_struct *wq = dev_to_wq(dev);
        int val;

        if (sscanf(buf, "%d", &val) != 1 || val <= 0)
                return -EINVAL;

        workqueue_set_max_active(wq, val);
        return count;
}

static struct device_attribute wq_sysfs_attrs[] = {
        __ATTR(per_cpu, 0444, wq_per_cpu_show, NULL),
        __ATTR(max_active, 0644, wq_max_active_show, wq_max_active_store),
        __ATTR_NULL,
};

static ssize_t wq_pool_id_show(struct device *dev,
                               struct device_attribute *attr, char *buf)
{
        struct workqueue_struct *wq = dev_to_wq(dev);
        struct worker_pool *pool;
        int written;

        rcu_read_lock_sched();
        pool = first_pwq(wq)->pool;
        written = scnprintf(buf, PAGE_SIZE, "%d\n", pool->id);
        rcu_read_unlock_sched();

        return written;
}

static ssize_t wq_nice_show(struct device *dev, struct device_attribute *attr,
                            char *buf)
{
        struct workqueue_struct *wq = dev_to_wq(dev);
        int written;

        rcu_read_lock_sched();
        written = scnprintf(buf, PAGE_SIZE, "%d\n",
                            first_pwq(wq)->pool->attrs->nice);
        rcu_read_unlock_sched();

        return written;
}

/* prepare workqueue_attrs for sysfs store operations */
static struct workqueue_attrs *wq_sysfs_prep_attrs(struct workqueue_struct *wq)
{
        struct workqueue_attrs *attrs;

        attrs = alloc_workqueue_attrs(GFP_KERNEL);
        if (!attrs)
                return NULL;

        rcu_read_lock_sched();
        copy_workqueue_attrs(attrs, first_pwq(wq)->pool->attrs);
        rcu_read_unlock_sched();
        return attrs;
}

static ssize_t wq_nice_store(struct device *dev, struct device_attribute *attr,
                             const char *buf, size_t count)
{
        struct workqueue_struct *wq = dev_to_wq(dev);
        struct workqueue_attrs *attrs;
        int ret;

        attrs = wq_sysfs_prep_attrs(wq);
        if (!attrs)
                return -ENOMEM;

        if (sscanf(buf, "%d", &attrs->nice) == 1 &&
            attrs->nice >= -20 && attrs->nice <= 19)
                ret = apply_workqueue_attrs(wq, attrs);
        else
                ret = -EINVAL;

        free_workqueue_attrs(attrs);
        return ret ?: count;
}

static ssize_t wq_cpumask_show(struct device *dev,
                               struct device_attribute *attr, char *buf)
{
        struct workqueue_struct *wq = dev_to_wq(dev);
        int written;

        rcu_read_lock_sched();
        written = cpumask_scnprintf(buf, PAGE_SIZE,
                                    first_pwq(wq)->pool->attrs->cpumask);
        rcu_read_unlock_sched();

        written += scnprintf(buf + written, PAGE_SIZE - written, "\n");
        return written;
}

static ssize_t wq_cpumask_store(struct device *dev,
                                struct device_attribute *attr,
                                const char *buf, size_t count)
{
        struct workqueue_struct *wq = dev_to_wq(dev);
        struct workqueue_attrs *attrs;
        int ret;

        attrs = wq_sysfs_prep_attrs(wq);
        if (!attrs)
                return -ENOMEM;

        ret = cpumask_parse(buf, attrs->cpumask);
        if (!ret)
                ret = apply_workqueue_attrs(wq, attrs);

        free_workqueue_attrs(attrs);
        return ret ?: count;
}

static struct device_attribute wq_sysfs_unbound_attrs[] = {
        __ATTR(pool_id, 0444, wq_pool_id_show, NULL),
        __ATTR(nice, 0644, wq_nice_show, wq_nice_store),
        __ATTR(cpumask, 0644, wq_cpumask_show, wq_cpumask_store),
        __ATTR_NULL,
};

static struct bus_type wq_subsys = {
        .name                           = "workqueue",
        .dev_attrs                      = wq_sysfs_attrs,
};

static int __init wq_sysfs_init(void)
{
        return subsys_virtual_register(&wq_subsys, NULL);
}
core_initcall(wq_sysfs_init);

static void wq_device_release(struct device *dev)
{
        struct wq_device *wq_dev = container_of(dev, struct wq_device, dev);

        kfree(wq_dev);
}

/**
 * workqueue_sysfs_register - make a workqueue visible in sysfs
 * @wq: the workqueue to register
 *
 * Expose @wq in sysfs under /sys/bus/workqueue/devices.
 * alloc_workqueue*() automatically calls this function if WQ_SYSFS is set
 * which is the preferred method.
 *
 * Workqueue user should use this function directly iff it wants to apply
 * workqueue_attrs before making the workqueue visible in sysfs; otherwise,
 * apply_workqueue_attrs() may race against userland updating the
 * attributes.
 *
 * Returns 0 on success, -errno on failure.
 */
int workqueue_sysfs_register(struct workqueue_struct *wq)
{
        struct wq_device *wq_dev;
        int ret;

        /*
         * Adjusting max_active or creating new pwqs by applyting
         * attributes breaks ordering guarantee.  Disallow exposing ordered
         * workqueues.
         */
        if (WARN_ON(wq->flags & __WQ_ORDERED))
                return -EINVAL;

        wq->wq_dev = wq_dev = kzalloc(sizeof(*wq_dev), GFP_KERNEL);
        if (!wq_dev)
                return -ENOMEM;

        wq_dev->wq = wq;
        wq_dev->dev.bus = &wq_subsys;
        wq_dev->dev.init_name = wq->name;
        wq_dev->dev.release = wq_device_release;

        /*
         * unbound_attrs are created separately.  Suppress uevent until
         * everything is ready.
         */
        dev_set_uevent_suppress(&wq_dev->dev, true);

        ret = device_register(&wq_dev->dev);
        if (ret) {
                kfree(wq_dev);
                wq->wq_dev = NULL;
                return ret;
        }

        if (wq->flags & WQ_UNBOUND) {
                struct device_attribute *attr;

                for (attr = wq_sysfs_unbound_attrs; attr->attr.name; attr++) {
                        ret = device_create_file(&wq_dev->dev, attr);
                        if (ret) {
                                device_unregister(&wq_dev->dev);
                                wq->wq_dev = NULL;
                                return ret;
                        }
                }
        }

        kobject_uevent(&wq_dev->dev.kobj, KOBJ_ADD);
        return 0;
}

/**
 * workqueue_sysfs_unregister - undo workqueue_sysfs_register()
 * @wq: the workqueue to unregister
 *
 * If @wq is registered to sysfs by workqueue_sysfs_register(), unregister.
 */
static void workqueue_sysfs_unregister(struct workqueue_struct *wq)
{
        struct wq_device *wq_dev = wq->wq_dev;

        if (!wq->wq_dev)
                return;

        wq->wq_dev = NULL;
        device_unregister(&wq_dev->dev);
}
#else   /* CONFIG_SYSFS */
static void workqueue_sysfs_unregister(struct workqueue_struct *wq)     { }
#endif  /* CONFIG_SYSFS */

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

/**
 * alloc_workqueue_attrs - allocate a workqueue_attrs
 * @gfp_mask: allocation mask to use
 *
 * Allocate a new workqueue_attrs, initialize with default settings and
 * return it.  Returns NULL on failure.
 */
struct workqueue_attrs *alloc_workqueue_attrs(gfp_t gfp_mask)
{
        struct workqueue_attrs *attrs;

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

        cpumask_setall(attrs->cpumask);
        return attrs;
fail:
        free_workqueue_attrs(attrs);
        return NULL;
}

static void copy_workqueue_attrs(struct workqueue_attrs *to,
                                 const struct workqueue_attrs *from)
{
        to->nice = from->nice;
        cpumask_copy(to->cpumask, from->cpumask);
}

/*
 * Hacky implementation of jhash of bitmaps which only considers the
 * specified number of bits.  We probably want a proper implementation in
 * include/linux/jhash.h.
 */
static u32 jhash_bitmap(const unsigned long *bitmap, int bits, u32 hash)
{
        int nr_longs = bits / BITS_PER_LONG;
        int nr_leftover = bits % BITS_PER_LONG;
        unsigned long leftover = 0;

        if (nr_longs)
                hash = jhash(bitmap, nr_longs * sizeof(long), hash);
        if (nr_leftover) {
                bitmap_copy(&leftover, bitmap + nr_longs, nr_leftover);
                hash = jhash(&leftover, sizeof(long), hash);
        }
        return hash;
}

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

        hash = jhash_1word(attrs->nice, hash);
        hash = jhash_bitmap(cpumask_bits(attrs->cpumask), nr_cpu_ids, hash);
        return hash;
}

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

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

        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, pool_mayday_timeout,
                    (unsigned long)pool);

        mutex_init(&pool->manager_arb);
        mutex_init(&pool->manager_mutex);
        idr_init(&pool->worker_idr);

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

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

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

        idr_destroy(&pool->worker_idr);
        free_workqueue_attrs(pool->attrs);
        kfree(pool);
}

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

        mutex_lock(&wq_pool_mutex);
        if (--pool->refcnt) {
                mutex_unlock(&wq_pool_mutex);
                return;
        }

        /* sanity checks */
        if (WARN_ON(!(pool->flags & POOL_DISASSOCIATED)) ||
            WARN_ON(!list_empty(&pool->worklist))) {
                mutex_unlock(&wq_pool_mutex);
                return;
        }

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

        mutex_unlock(&wq_pool_mutex);

        /*
         * Become the manager and destroy all workers.  Grabbing
         * manager_arb prevents @pool's workers from blocking on
         * manager_mutex.
         */
        mutex_lock(&pool->manager_arb);
        mutex_lock(&pool->manager_mutex);
        spin_lock_irq(&pool->lock);

        while ((worker = first_worker(pool)))
                destroy_worker(worker);
        WARN_ON(pool->nr_workers || pool->nr_idle);

        spin_unlock_irq(&pool->lock);
        mutex_unlock(&pool->manager_mutex);
        mutex_unlock(&pool->manager_arb);

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

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

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

        mutex_lock(&wq_pool_mutex);

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

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

        if (workqueue_freezing)
                pool->flags |= POOL_FREEZING;

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

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

        /* create and start the initial worker */
        if (create_and_start_worker(pool) < 0)
                goto fail;

        /* install */
        hash_add(unbound_pool_hash, &pool->hash_node, hash);
out_unlock:
        mutex_unlock(&wq_pool_mutex);
        return pool;
fail:
        mutex_unlock(&wq_pool_mutex);
        if (pool)
                put_unbound_pool(pool);
        return NULL;
}

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

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

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

        /*
         * Unlink @pwq.  Synchronization against wq->mutex isn't strictly
         * necessary on release but do it anyway.  It's easier to verify
         * and consistent with the linking path.
         */
        mutex_lock(&wq->mutex);
        list_del_rcu(&pwq->pwqs_node);
        is_last = list_empty(&wq->pwqs);
        mutex_unlock(&wq->mutex);

        put_unbound_pool(pool);
        call_rcu_sched(&pwq->rcu, rcu_free_pwq);

        /*
         * If we're the last pwq going away, @wq is already dead and no one
         * is gonna access it anymore.  Free it.
         */
        if (is_last)
                kfree(wq);
}

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

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

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

        spin_lock_irq(&pwq->pool->lock);

        if (!freezable || !(pwq->pool->flags & POOL_FREEZING)) {
                pwq->max_active = wq->saved_max_active;

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

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

        spin_unlock_irq(&pwq->pool->lock);
}

static void init_and_link_pwq(struct pool_workqueue *pwq,
                              struct workqueue_struct *wq,
                              struct worker_pool *pool,
                              struct pool_workqueue **p_last_pwq)
{
        BUG_ON((unsigned long)pwq & WORK_STRUCT_FLAG_MASK);

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

        mutex_lock(&wq->mutex);

        /*
         * Set the matching work_color.  This is synchronized with
         * wq->mutex to avoid confusing flush_workqueue().
         */
        if (p_last_pwq)
                *p_last_pwq = first_pwq(wq);
        pwq->work_color = wq->work_color;

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

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

        mutex_unlock(&wq->mutex);
}

/**
 * apply_workqueue_attrs - apply new workqueue_attrs to an unbound workqueue
 * @wq: the target workqueue
 * @attrs: the workqueue_attrs to apply, allocated with alloc_workqueue_attrs()
 *
 * Apply @attrs to an unbound workqueue @wq.  If @attrs doesn't match the
 * current attributes, a new pwq is created and made the first pwq which
 * will serve all new work items.  Older pwqs are released as in-flight
 * work items finish.  Note that a work item which repeatedly requeues
 * itself back-to-back will stay on its current pwq.
 *
 * Performs GFP_KERNEL allocations.  Returns 0 on success and -errno on
 * failure.
 */
int apply_workqueue_attrs(struct workqueue_struct *wq,
                          const struct workqueue_attrs *attrs)
{
        struct pool_workqueue *pwq, *last_pwq;
        struct worker_pool *pool;

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

        /* creating multiple pwqs breaks ordering guarantee */
        if (WARN_ON((wq->flags & __WQ_ORDERED) && !list_empty(&wq->pwqs)))
                return -EINVAL;

        pwq = kmem_cache_zalloc(pwq_cache, GFP_KERNEL);
        if (!pwq)
                return -ENOMEM;

        pool = get_unbound_pool(attrs);
        if (!pool) {
                kmem_cache_free(pwq_cache, pwq);
                return -ENOMEM;
        }

        init_and_link_pwq(pwq, wq, pool, &last_pwq);
        if (last_pwq) {
                spin_lock_irq(&last_pwq->pool->lock);
                put_pwq(last_pwq);
                spin_unlock_irq(&last_pwq->pool->lock);
        }

        return 0;
}

static int alloc_and_link_pwqs(struct workqueue_struct *wq)
{
        bool highpri = wq->flags & WQ_HIGHPRI;
        int cpu;

        if (!(wq->flags & WQ_UNBOUND)) {
                wq->cpu_pwqs = alloc_percpu(struct pool_workqueue);
                if (!wq->cpu_pwqs)
                        return -ENOMEM;

                for_each_possible_cpu(cpu) {
                        struct pool_workqueue *pwq =
                                per_cpu_ptr(wq->cpu_pwqs, cpu);
                        struct worker_pool *cpu_pools =
                                per_cpu(cpu_worker_pools, cpu);

                        init_and_link_pwq(pwq, wq, &cpu_pools[highpri], NULL);
                }
                return 0;
        } else {
                return apply_workqueue_attrs(wq, unbound_std_wq_attrs[highpri]);
        }
}

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;
        struct pool_workqueue *pwq;
        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)
                return NULL;

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

        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->mutex);
        atomic_set(&wq->nr_pwqs_to_flush, 0);
        INIT_LIST_HEAD(&wq->pwqs);
        INIT_LIST_HEAD(&wq->flusher_queue);
        INIT_LIST_HEAD(&wq->flusher_overflow);
        INIT_LIST_HEAD(&wq->maydays);

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

        if (alloc_and_link_pwqs(wq) < 0)
                goto err_free_wq;

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

                rescuer = alloc_worker();
                if (!rescuer)
                        goto err_destroy;

                rescuer->rescue_wq = wq;
                rescuer->task = kthread_create(rescuer_thread, rescuer, "%s",
                                               wq->name);
                if (IS_ERR(rescuer->task)) {
                        kfree(rescuer);
                        goto err_destroy;
                }

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

        if ((wq->flags & WQ_SYSFS) && workqueue_sysfs_register(wq))
                goto err_destroy;

        /*
         * wq_pool_mutex protects global freeze state and workqueues list.
         * Grab it, adjust max_active and add the new @wq to workqueues
         * list.
         */
        mutex_lock(&wq_pool_mutex);

        mutex_lock(&wq->mutex);
        for_each_pwq(pwq, wq)
                pwq_adjust_max_active(pwq);
        mutex_unlock(&wq->mutex);

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

        mutex_unlock(&wq_pool_mutex);

        return wq;

err_free_wq:
        kfree(wq);
        return NULL;
err_destroy:
        destroy_workqueue(wq);
        return NULL;
}
EXPORT_SYMBOL_GPL(__alloc_workqueue_key);

/**
 * destroy_workqueue - safely terminate a workqueue
 * @wq: target workqueue
 *
 * Safely destroy a workqueue. All work currently pending will be done first.
 */
void destroy_workqueue(struct workqueue_struct *wq)
{
        struct pool_workqueue *pwq;

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

        /* sanity checks */
        mutex_lock(&wq->mutex);
        for_each_pwq(pwq, wq) {
                int i;

                for (i = 0; i < WORK_NR_COLORS; i++) {
                        if (WARN_ON(pwq->nr_in_flight[i])) {
                                mutex_unlock(&wq->mutex);
                                return;
                        }
                }

                if (WARN_ON(pwq->refcnt > 1) ||
                    WARN_ON(pwq->nr_active) ||
                    WARN_ON(!list_empty(&pwq->delayed_works))) {
                        mutex_unlock(&wq->mutex);
                        return;
                }
        }
        mutex_unlock(&wq->mutex);

        /*
         * wq list is used to freeze wq, remove from list after
         * flushing is complete in case freeze races us.
         */
        mutex_lock(&wq_pool_mutex);
        list_del_init(&wq->list);
        mutex_unlock(&wq_pool_mutex);

        workqueue_sysfs_unregister(wq);

        if (wq->rescuer) {
                kthread_stop(wq->rescuer->task);
                kfree(wq->rescuer);
                wq->rescuer = NULL;
        }

        if (!(wq->flags & WQ_UNBOUND)) {
                /*
                 * The base ref is never dropped on per-cpu pwqs.  Directly
                 * free the pwqs and wq.
                 */
                free_percpu(wq->cpu_pwqs);
                kfree(wq);
        } else {
                /*
                 * We're the sole accessor of @wq at this point.  Directly
                 * access the first pwq and put the base ref.  As both pwqs
                 * and pools are sched-RCU protected, the lock operations
                 * are safe.  @wq will be freed when the last pwq is
                 * released.
                 */
                pwq = list_first_entry(&wq->pwqs, struct pool_workqueue,
                                       pwqs_node);
                spin_lock_irq(&pwq->pool->lock);
                put_pwq(pwq);
                spin_unlock_irq(&pwq->pool->lock);
        }
}
EXPORT_SYMBOL_GPL(destroy_workqueue);

/**
 * workqueue_set_max_active - adjust max_active of a workqueue
 * @wq: target workqueue
 * @max_active: new max_active value.
 *
 * Set max_active of @wq to @max_active.
 *
 * CONTEXT:
 * Don't call from IRQ context.
 */
void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
{
        struct pool_workqueue *pwq;

        /* disallow meddling with max_active for ordered workqueues */
        if (WARN_ON(wq->flags & __WQ_ORDERED))
                return;

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

        mutex_lock(&wq->mutex);

        wq->saved_max_active = max_active;

        for_each_pwq(pwq, wq)
                pwq_adjust_max_active(pwq);

        mutex_unlock(&wq->mutex);
}
EXPORT_SYMBOL_GPL(workqueue_set_max_active);

/**
 * current_is_workqueue_rescuer - is %current workqueue rescuer?
 *
 * Determine whether %current is a workqueue rescuer.  Can be used from
 * work functions to determine whether it's being run off the rescuer task.
 */
bool current_is_workqueue_rescuer(void)
{
        struct worker *worker = current_wq_worker();

        return worker && worker->rescue_wq;
}

/**
 * workqueue_congested - test whether a workqueue is congested
 * @cpu: CPU in question
 * @wq: target workqueue
 *
 * Test whether @wq's cpu workqueue for @cpu is congested.  There is
 * no synchronization around this function and the test result is
 * unreliable and only useful as advisory hints or for debugging.
 *
 * RETURNS:
 * %true if congested, %false otherwise.
 */
bool workqueue_congested(int cpu, struct workqueue_struct *wq)
{
        struct pool_workqueue *pwq;
        bool ret;

        rcu_read_lock_sched();

        if (!(wq->flags & WQ_UNBOUND))
                pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
        else
                pwq = first_pwq(wq);

        ret = !list_empty(&pwq->delayed_works);
        rcu_read_unlock_sched();

        return ret;
}
EXPORT_SYMBOL_GPL(workqueue_congested);

/**
 * work_busy - test whether a work is currently pending or running
 * @work: the work to be tested
 *
 * Test whether @work is currently pending or running.  There is no
 * synchronization around this function and the test result is
 * unreliable and only useful as advisory hints or for debugging.
 *
 * RETURNS:
 * OR'd bitmask of WORK_BUSY_* bits.
 */
unsigned int work_busy(struct work_struct *work)
{
        struct worker_pool *pool;
        unsigned long flags;
        unsigned int ret = 0;

        if (work_pending(work))
                ret |= WORK_BUSY_PENDING;

        local_irq_save(flags);
        pool = get_work_pool(work);
        if (pool) {
                spin_lock(&pool->lock);
                if (find_worker_executing_work(pool, work))
                        ret |= WORK_BUSY_RUNNING;
                spin_unlock(&pool->lock);
        }
        local_irq_restore(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, pwq and
 * pool which make migrating pending and scheduled works very
 * difficult to implement without impacting hot paths.  Secondly,
 * worker pools serve mix of short, long and very long running works making
 * blocked draining impractical.
 *
 * This is solved by allowing the pools to be disassociated from the CPU
 * running as an unbound one and allowing it to be reattached later if the
 * cpu comes back online.
 */

static void wq_unbind_fn(struct work_struct *work)
{
        int cpu = smp_processor_id();
        struct worker_pool *pool;
        struct worker *worker;
        int wi;

        for_each_cpu_worker_pool(pool, cpu) {
                WARN_ON_ONCE(cpu != smp_processor_id());

                mutex_lock(&pool->manager_mutex);
                spin_lock_irq(&pool->lock);

                /*
                 * We've blocked all manager operations.  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_pool_worker(worker, wi, pool)
                        worker->flags |= WORKER_UNBOUND;

                pool->flags |= POOL_DISASSOCIATED;

                spin_unlock_irq(&pool->lock);
                mutex_unlock(&pool->manager_mutex);
        }

        /*
         * 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.  Pools on
         * @cpu now behave as unbound (in terms of concurrency management)
         * pools which are 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_cpu_worker_pool(pool, cpu)
                atomic_set(&pool->nr_running, 0);
}

/**
 * rebind_workers - rebind all workers of a pool to the associated CPU
 * @pool: pool of interest
 *
 * @pool->cpu is coming online.  Rebind all workers to the CPU.
 */
static void rebind_workers(struct worker_pool *pool)
{
        struct worker *worker;
        int wi;

        lockdep_assert_held(&pool->manager_mutex);

        /*
         * Restore CPU affinity of all workers.  As all idle workers should
         * be on the run-queue of the associated CPU before any local
         * wake-ups for concurrency management happen, restore CPU affinty
         * of all workers first and then clear UNBOUND.  As we're called
         * from CPU_ONLINE, the following shouldn't fail.
         */
        for_each_pool_worker(worker, wi, pool)
                WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
                                                  pool->attrs->cpumask) < 0);

        spin_lock_irq(&pool->lock);

        for_each_pool_worker(worker, wi, pool) {
                unsigned int worker_flags = worker->flags;

                /*
                 * A bound idle worker should actually be on the runqueue
                 * of the associated CPU for local wake-ups targeting it to
                 * work.  Kick all idle workers so that they migrate to the
                 * associated CPU.  Doing this in the same loop as
                 * replacing UNBOUND with REBOUND is safe as no worker will
                 * be bound before @pool->lock is released.
                 */
                if (worker_flags & WORKER_IDLE)
                        wake_up_process(worker->task);

                /*
                 * We want to clear UNBOUND but can't directly call
                 * worker_clr_flags() or adjust nr_running.  Atomically
                 * replace UNBOUND with another NOT_RUNNING flag REBOUND.
                 * @worker will clear REBOUND using worker_clr_flags() when
                 * it initiates the next execution cycle thus restoring
                 * concurrency management.  Note that when or whether
                 * @worker clears REBOUND doesn't affect correctness.
                 *
                 * ACCESS_ONCE() is necessary because @worker->flags may be
                 * tested without holding any lock in
                 * wq_worker_waking_up().  Without it, NOT_RUNNING test may
                 * fail incorrectly leading to premature concurrency
                 * management operations.
                 */
                WARN_ON_ONCE(!(worker_flags & WORKER_UNBOUND));
                worker_flags |= WORKER_REBOUND;
                worker_flags &= ~WORKER_UNBOUND;
                ACCESS_ONCE(worker->flags) = worker_flags;
        }

        spin_unlock_irq(&pool->lock);
}

/**
 * restore_unbound_workers_cpumask - restore cpumask of unbound workers
 * @pool: unbound pool of interest
 * @cpu: the CPU which is coming up
 *
 * An unbound pool may end up with a cpumask which doesn't have any online
 * CPUs.  When a worker of such pool get scheduled, the scheduler resets
 * its cpus_allowed.  If @cpu is in @pool's cpumask which didn't have any
 * online CPU before, cpus_allowed of all its workers should be restored.
 */
static void restore_unbound_workers_cpumask(struct worker_pool *pool, int cpu)
{
        static cpumask_t cpumask;
        struct worker *worker;
        int wi;

        lockdep_assert_held(&pool->manager_mutex);

        /* is @cpu allowed for @pool? */
        if (!cpumask_test_cpu(cpu, pool->attrs->cpumask))
                return;

        /* is @cpu the only online CPU? */
        cpumask_and(&cpumask, pool->attrs->cpumask, cpu_online_mask);
        if (cpumask_weight(&cpumask) != 1)
                return;

        /* as we're called from CPU_ONLINE, the following shouldn't fail */
        for_each_pool_worker(worker, wi, pool)
                WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
                                                  pool->attrs->cpumask) < 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)
{
        int cpu = (unsigned long)hcpu;
        struct worker_pool *pool;
        int pi;

        switch (action & ~CPU_TASKS_FROZEN) {
        case CPU_UP_PREPARE:
                for_each_cpu_worker_pool(pool, cpu) {
                        if (pool->nr_workers)
                                continue;
                        if (create_and_start_worker(pool) < 0)
                                return NOTIFY_BAD;
                }
                break;

        case CPU_DOWN_FAILED:
        case CPU_ONLINE:
                mutex_lock(&wq_pool_mutex);

                for_each_pool(pool, pi) {
                        mutex_lock(&pool->manager_mutex);

                        if (pool->cpu == cpu) {
                                spin_lock_irq(&pool->lock);
                                pool->flags &= ~POOL_DISASSOCIATED;
                                spin_unlock_irq(&pool->lock);

                                rebind_workers(pool);
                        } else if (pool->cpu < 0) {
                                restore_unbound_workers_cpumask(pool, cpu);
                        }

                        mutex_unlock(&pool->manager_mutex);
                }

                mutex_unlock(&wq_pool_mutex);
                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)
{
        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, wq_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);
}

/**
 * work_on_cpu - run a function in user context on a particular cpu
 * @cpu: the cpu to run on
 * @fn: the function to run
 * @arg: the function arg
 *
 * This will return the value @fn returns.
 * It is up to the caller to ensure that the cpu doesn't go offline.
 * The caller must not hold any locks which would prevent @fn from completing.
 */
long work_on_cpu(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

/**
 * freeze_workqueues_begin - begin freezing workqueues
 *
 * Start freezing workqueues.  After this function returns, all freezable
 * workqueues will queue new works to their delayed_works list instead of
 * pool->worklist.
 *
 * CONTEXT:
 * Grabs and releases wq_pool_mutex, wq->mutex and pool->lock's.
 */
void freeze_workqueues_begin(void)
{
        struct worker_pool *pool;
        struct workqueue_struct *wq;
        struct pool_workqueue *pwq;
        int pi;

        mutex_lock(&wq_pool_mutex);

        WARN_ON_ONCE(workqueue_freezing);
        workqueue_freezing = true;

        /* set FREEZING */
        for_each_pool(pool, pi) {
                spin_lock_irq(&pool->lock);
                WARN_ON_ONCE(pool->flags & POOL_FREEZING);
                pool->flags |= POOL_FREEZING;
                spin_unlock_irq(&pool->lock);
        }

        list_for_each_entry(wq, &workqueues, list) {
                mutex_lock(&wq->mutex);
                for_each_pwq(pwq, wq)
                        pwq_adjust_max_active(pwq);
                mutex_unlock(&wq->mutex);
        }

        mutex_unlock(&wq_pool_mutex);
}

/**
 * freeze_workqueues_busy - are freezable workqueues still busy?
 *
 * Check whether freezing is complete.  This function must be called
 * between freeze_workqueues_begin() and thaw_workqueues().
 *
 * CONTEXT:
 * Grabs and releases wq_pool_mutex.
 *
 * RETURNS:
 * %true if some freezable workqueues are still busy.  %false if freezing
 * is complete.
 */
bool freeze_workqueues_busy(void)
{
        bool busy = false;
        struct workqueue_struct *wq;
        struct pool_workqueue *pwq;

        mutex_lock(&wq_pool_mutex);

        WARN_ON_ONCE(!workqueue_freezing);

        list_for_each_entry(wq, &workqueues, list) {
                if (!(wq->flags & WQ_FREEZABLE))
                        continue;
                /*
                 * nr_active is monotonically decreasing.  It's safe
                 * to peek without lock.
                 */
                rcu_read_lock_sched();
                for_each_pwq(pwq, wq) {
                        WARN_ON_ONCE(pwq->nr_active < 0);
                        if (pwq->nr_active) {
                                busy = true;
                                rcu_read_unlock_sched();
                                goto out_unlock;
                        }
                }
                rcu_read_unlock_sched();
        }
out_unlock:
        mutex_unlock(&wq_pool_mutex);
        return busy;
}

/**
 * thaw_workqueues - thaw workqueues
 *
 * Thaw workqueues.  Normal queueing is restored and all collected
 * frozen works are transferred to their respective pool worklists.
 *
 * CONTEXT:
 * Grabs and releases wq_pool_mutex, wq->mutex and pool->lock's.
 */
void thaw_workqueues(void)
{
        struct workqueue_struct *wq;
        struct pool_workqueue *pwq;
        struct worker_pool *pool;
        int pi;

        mutex_lock(&wq_pool_mutex);

        if (!workqueue_freezing)
                goto out_unlock;

        /* clear FREEZING */
        for_each_pool(pool, pi) {
                spin_lock_irq(&pool->lock);
                WARN_ON_ONCE(!(pool->flags & POOL_FREEZING));
                pool->flags &= ~POOL_FREEZING;
                spin_unlock_irq(&pool->lock);
        }

        /* restore max_active and repopulate worklist */
        list_for_each_entry(wq, &workqueues, list) {
                mutex_lock(&wq->mutex);
                for_each_pwq(pwq, wq)
                        pwq_adjust_max_active(pwq);
                mutex_unlock(&wq->mutex);
        }

        workqueue_freezing = false;
out_unlock:
        mutex_unlock(&wq_pool_mutex);
}
#endif /* CONFIG_FREEZER */

static int __init init_workqueues(void)
{
        int std_nice[NR_STD_WORKER_POOLS] = { 0, HIGHPRI_NICE_LEVEL };
        int i, cpu;

        /* make sure we have enough bits for OFFQ pool ID */
        BUILD_BUG_ON((1LU << (BITS_PER_LONG - WORK_OFFQ_POOL_SHIFT)) <
                     WORK_CPU_END * NR_STD_WORKER_POOLS);

        WARN_ON(__alignof__(struct pool_workqueue) < __alignof__(long long));

        pwq_cache = KMEM_CACHE(pool_workqueue, SLAB_PANIC);

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

        /* initialize CPU pools */
        for_each_possible_cpu(cpu) {
                struct worker_pool *pool;

                i = 0;
                for_each_cpu_worker_pool(pool, cpu) {
                        BUG_ON(init_worker_pool(pool));
                        pool->cpu = cpu;
                        cpumask_copy(pool->attrs->cpumask, cpumask_of(cpu));
                        pool->attrs->nice = std_nice[i++];

                        /* alloc pool ID */
                        mutex_lock(&wq_pool_mutex);
                        BUG_ON(worker_pool_assign_id(pool));
                        mutex_unlock(&wq_pool_mutex);
                }
        }

        /* create the initial worker */
        for_each_online_cpu(cpu) {
                struct worker_pool *pool;

                for_each_cpu_worker_pool(pool, cpu) {
                        pool->flags &= ~POOL_DISASSOCIATED;
                        BUG_ON(create_and_start_worker(pool) < 0);
                }
        }

        /* create default unbound wq attrs */
        for (i = 0; i < NR_STD_WORKER_POOLS; i++) {
                struct workqueue_attrs *attrs;

                BUG_ON(!(attrs = alloc_workqueue_attrs(GFP_KERNEL)));

                attrs->nice = std_nice[i];
                cpumask_setall(attrs->cpumask);

                unbound_std_wq_attrs[i] = attrs;
        }

        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);