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[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.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/module.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/signal.h>
#include <linux/completion.h>
#include <linux/workqueue.h>
#include <linux/slab.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/kthread.h>
#include <linux/hardirq.h>
#include <linux/mempolicy.h>
#include <linux/freezer.h>
#include <linux/kallsyms.h>
#include <linux/debug_locks.h>
#include <linux/lockdep.h>
#include <linux/idr.h>

#include "workqueue_sched.h"

enum {
        /* global_cwq flags */
        GCWQ_MANAGE_WORKERS     = 1 << 0,       /* need to manage workers */
        GCWQ_MANAGING_WORKERS   = 1 << 1,       /* managing workers */
        GCWQ_DISASSOCIATED      = 1 << 2,       /* cpu can't serve workers */
        GCWQ_FREEZING           = 1 << 3,       /* freeze in progress */
        GCWQ_HIGHPRI_PENDING    = 1 << 4,       /* highpri works on queue */

        /* 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_ROGUE            = 1 << 4,       /* not bound to any cpu */
        WORKER_REBIND           = 1 << 5,       /* mom is home, come back */
        WORKER_CPU_INTENSIVE    = 1 << 6,       /* cpu intensive */
        WORKER_UNBOUND          = 1 << 7,       /* worker is unbound */

        WORKER_NOT_RUNNING      = WORKER_PREP | WORKER_ROGUE | WORKER_REBIND |
                                  WORKER_CPU_INTENSIVE | WORKER_UNBOUND,

        /* gcwq->trustee_state */
        TRUSTEE_START           = 0,            /* start */
        TRUSTEE_IN_CHARGE       = 1,            /* trustee in charge of gcwq */
        TRUSTEE_BUTCHER         = 2,            /* butcher workers */
        TRUSTEE_RELEASE         = 3,            /* release workers */
        TRUSTEE_DONE            = 4,            /* trustee is done */

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

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

        MAYDAY_INITIAL_TIMEOUT  = HZ / 100,     /* call for help after 10ms */
        MAYDAY_INTERVAL         = HZ / 10,      /* and then every 100ms */
        CREATE_COOLDOWN         = HZ,           /* time to breath after fail */
        TRUSTEE_COOLDOWN        = HZ / 10,      /* for trustee draining */

        /*
         * Rescue workers are used only on emergencies and shared by
         * all cpus.  Give -20.
         */
        RESCUER_NICE_LEVEL      = -20,
};

/*
 * Structure fields follow one of the following exclusion rules.
 *
 * I: Modifiable by initialization/destruction paths and read-only for
 *    everyone else.
 *
 * P: Preemption protected.  Disabling preemption is enough and should
 *    only be modified and accessed from the local cpu.
 *
 * L: gcwq->lock protected.  Access with gcwq->lock held.
 *
 * X: During normal operation, modification requires gcwq->lock and
 *    should be done only from local cpu.  Either disabling preemption
 *    on local cpu or grabbing gcwq->lock is enough for read access.
 *    If GCWQ_DISASSOCIATED is set, it's identical to L.
 *
 * F: wq->flush_mutex protected.
 *
 * W: workqueue_lock protected.
 */

struct global_cwq;

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

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

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

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

        /* workers are chained either in the idle_list or busy_hash */
        struct list_head        idle_list;      /* X: list of idle workers */
        struct hlist_head       busy_hash[BUSY_WORKER_HASH_SIZE];
                                                /* L: hash of busy workers */

        struct timer_list       idle_timer;     /* L: worker idle timeout */
        struct timer_list       mayday_timer;   /* L: SOS timer for dworkers */

        struct ida              worker_ida;     /* L: for worker IDs */

        struct task_struct      *trustee;       /* L: for gcwq shutdown */
        unsigned int            trustee_state;  /* L: trustee state */
        wait_queue_head_t       trustee_wait;   /* trustee wait */
        struct worker           *first_idle;    /* L: first idle worker */
} ____cacheline_aligned_in_smp;

/*
 * The per-CPU workqueue.  The lower WORK_STRUCT_FLAG_BITS of
 * work_struct->data are used for flags and thus cwqs need to be
 * aligned at two's power of the number of flag bits.
 */
struct cpu_workqueue_struct {
        struct global_cwq       *gcwq;          /* I: the associated gcwq */
        struct workqueue_struct *wq;            /* I: the owning workqueue */
        int                     work_color;     /* L: current color */
        int                     flush_color;    /* L: flushing color */
        int                     nr_in_flight[WORK_NR_COLORS];
                                                /* L: nr of in_flight works */
        int                     nr_active;      /* L: nr of active works */
        int                     max_active;     /* L: max active works */
        struct list_head        delayed_works;  /* L: delayed works */
};

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

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

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

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

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

        int                     saved_max_active; /* W: saved cwq max_active */
        const char              *name;          /* I: workqueue name */
#ifdef CONFIG_LOCKDEP
        struct lockdep_map      lockdep_map;
#endif
};

struct workqueue_struct *system_wq __read_mostly;
struct workqueue_struct *system_long_wq __read_mostly;
struct workqueue_struct *system_nrt_wq __read_mostly;
struct workqueue_struct *system_unbound_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_wq);
EXPORT_SYMBOL_GPL(system_long_wq);
EXPORT_SYMBOL_GPL(system_nrt_wq);
EXPORT_SYMBOL_GPL(system_unbound_wq);

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

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

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

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

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

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

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

#ifdef CONFIG_DEBUG_OBJECTS_WORK

static struct debug_obj_descr work_debug_descr;

/*
 * 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",
        .fixup_init     = work_fixup_init,
        .fixup_activate = work_fixup_activate,
        .fixup_free     = work_fixup_free,
};

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

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

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

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

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

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

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

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

static int worker_thread(void *__worker);

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

static atomic_t *get_gcwq_nr_running(unsigned int cpu)
{
        if (cpu != WORK_CPU_UNBOUND)
                return &per_cpu(gcwq_nr_running, cpu);
        else
                return &unbound_gcwq_nr_running;
}

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

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

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

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

/*
 * A work's data points to the cwq with WORK_STRUCT_CWQ set while the
 * work is on queue.  Once execution starts, WORK_STRUCT_CWQ is
 * cleared and the work data contains the cpu number it was last on.
 *
 * set_work_{cwq|cpu}() and clear_work_data() can be used to set the
 * cwq, cpu or clear work->data.  These functions should only be
 * called while the work is owned - ie. while the PENDING bit is set.
 *
 * get_work_[g]cwq() can be used to obtain the gcwq or cwq
 * corresponding to a work.  gcwq is available once the work has been
 * queued anywhere after initialization.  cwq is available only from
 * queueing until execution starts.
 */
static inline void set_work_data(struct work_struct *work, unsigned long data,
                                 unsigned long flags)
{
        BUG_ON(!work_pending(work));
        atomic_long_set(&work->data, data | flags | work_static(work));
}

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

static void set_work_cpu(struct work_struct *work, unsigned int cpu)
{
        set_work_data(work, cpu << WORK_STRUCT_FLAG_BITS, WORK_STRUCT_PENDING);
}

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

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

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

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

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

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

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

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

static bool __need_more_worker(struct global_cwq *gcwq)
{
        return !atomic_read(get_gcwq_nr_running(gcwq->cpu)) ||
                gcwq->flags & GCWQ_HIGHPRI_PENDING;
}

/*
 * Need to wake up a worker?  Called from anything but currently
 * running workers.
 */
static bool need_more_worker(struct global_cwq *gcwq)
{
        return !list_empty(&gcwq->worklist) && __need_more_worker(gcwq);
}

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

/* Do I need to keep working?  Called from currently running workers. */
static bool keep_working(struct global_cwq *gcwq)
{
        atomic_t *nr_running = get_gcwq_nr_running(gcwq->cpu);

        return !list_empty(&gcwq->worklist) &&
                (atomic_read(nr_running) <= 1 ||
                 gcwq->flags & GCWQ_HIGHPRI_PENDING);
}

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

/* Do I need to be the manager? */
static bool need_to_manage_workers(struct global_cwq *gcwq)
{
        return need_to_create_worker(gcwq) || gcwq->flags & GCWQ_MANAGE_WORKERS;
}

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

        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 global_cwq *gcwq)
{
        if (unlikely(list_empty(&gcwq->idle_list)))
                return NULL;

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

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

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

        if (likely(!(worker->flags & WORKER_NOT_RUNNING)))
                atomic_inc(get_gcwq_nr_running(cpu));
}

/**
 * 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,
                                       unsigned int cpu)
{
        struct worker *worker = kthread_data(task), *to_wakeup = NULL;
        struct global_cwq *gcwq = get_gcwq(cpu);
        atomic_t *nr_running = get_gcwq_nr_running(cpu);

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

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

        /*
         * The counterpart of the following dec_and_test, implied mb,
         * worklist not empty test sequence is in insert_work().
         * Please read comment there.
         *
         * NOT_RUNNING is clear.  This means that trustee is not in
         * charge and we're running on the local cpu w/ rq lock held
         * and preemption disabled, which in turn means that none else
         * could be manipulating idle_list, so dereferencing idle_list
         * without gcwq lock is safe.
         */
        if (atomic_dec_and_test(nr_running) && !list_empty(&gcwq->worklist))
                to_wakeup = first_worker(gcwq);
        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(gcwq->lock)
 */
static inline void worker_set_flags(struct worker *worker, unsigned int flags,
                                    bool wakeup)
{
        struct global_cwq *gcwq = worker->gcwq;

        WARN_ON_ONCE(worker->task != current);

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

                if (wakeup) {
                        if (atomic_dec_and_test(nr_running) &&
                            !list_empty(&gcwq->worklist))
                                wake_up_worker(gcwq);
                } else
                        atomic_dec(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(gcwq->lock)
 */
static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
{
        struct global_cwq *gcwq = worker->gcwq;
        unsigned int oflags = worker->flags;

        WARN_ON_ONCE(worker->task != current);

        worker->flags &= ~flags;

        /* if transitioning out of NOT_RUNNING, increment nr_running */
        if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
                if (!(worker->flags & WORKER_NOT_RUNNING))
                        atomic_inc(get_gcwq_nr_running(gcwq->cpu));
}

/**
 * busy_worker_head - return the busy hash head for a work
 * @gcwq: gcwq of interest
 * @work: work to be hashed
 *
 * Return hash head of @gcwq for @work.
 *
 * CONTEXT:
 * spin_lock_irq(gcwq->lock).
 *
 * RETURNS:
 * Pointer to the hash head.
 */
static struct hlist_head *busy_worker_head(struct global_cwq *gcwq,
                                           struct work_struct *work)
{
        const int base_shift = ilog2(sizeof(struct work_struct));
        unsigned long v = (unsigned long)work;

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

        return &gcwq->busy_hash[v];
}

/**
 * __find_worker_executing_work - find worker which is executing a work
 * @gcwq: gcwq of interest
 * @bwh: hash head as returned by busy_worker_head()
 * @work: work to find worker for
 *
 * Find a worker which is executing @work on @gcwq.  @bwh should be
 * the hash head obtained by calling busy_worker_head() with the same
 * work.
 *
 * CONTEXT:
 * spin_lock_irq(gcwq->lock).
 *
 * RETURNS:
 * Pointer to worker which is executing @work if found, NULL
 * otherwise.
 */
static struct worker *__find_worker_executing_work(struct global_cwq *gcwq,
                                                   struct hlist_head *bwh,
                                                   struct work_struct *work)
{
        struct worker *worker;
        struct hlist_node *tmp;

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

/**
 * find_worker_executing_work - find worker which is executing a work
 * @gcwq: gcwq of interest
 * @work: work to find worker for
 *
 * Find a worker which is executing @work on @gcwq.  This function is
 * identical to __find_worker_executing_work() except that this
 * function calculates @bwh itself.
 *
 * CONTEXT:
 * spin_lock_irq(gcwq->lock).
 *
 * RETURNS:
 * Pointer to worker which is executing @work if found, NULL
 * otherwise.
 */
static struct worker *find_worker_executing_work(struct global_cwq *gcwq,
                                                 struct work_struct *work)
{
        return __find_worker_executing_work(gcwq, busy_worker_head(gcwq, work),
                                            work);
}

/**
 * gcwq_determine_ins_pos - find insertion position
 * @gcwq: gcwq of interest
 * @cwq: cwq a work is being queued for
 *
 * A work for @cwq is about to be queued on @gcwq, determine insertion
 * position for the work.  If @cwq is for HIGHPRI wq, the work is
 * queued at the head of the queue but in FIFO order with respect to
 * other HIGHPRI works; otherwise, at the end of the queue.  This
 * function also sets GCWQ_HIGHPRI_PENDING flag to hint @gcwq that
 * there are HIGHPRI works pending.
 *
 * CONTEXT:
 * spin_lock_irq(gcwq->lock).
 *
 * RETURNS:
 * Pointer to inserstion position.
 */
static inline struct list_head *gcwq_determine_ins_pos(struct global_cwq *gcwq,
                                               struct cpu_workqueue_struct *cwq)
{
        struct work_struct *twork;

        if (likely(!(cwq->wq->flags & WQ_HIGHPRI)))
                return &gcwq->worklist;

        list_for_each_entry(twork, &gcwq->worklist, entry) {
                struct cpu_workqueue_struct *tcwq = get_work_cwq(twork);

                if (!(tcwq->wq->flags & WQ_HIGHPRI))
                        break;
        }

        gcwq->flags |= GCWQ_HIGHPRI_PENDING;
        return &twork->entry;
}

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

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

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

        list_add_tail(&work->entry, head);

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

        if (__need_more_worker(gcwq))
                wake_up_worker(gcwq);
}

static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
                         struct work_struct *work)
{
        struct global_cwq *gcwq;
        struct cpu_workqueue_struct *cwq;
        struct list_head *worklist;
        unsigned int work_flags;
        unsigned long flags;

        debug_work_activate(work);

        if (WARN_ON_ONCE(wq->flags & WQ_DYING))
                return;

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

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

                /*
                 * It's multi cpu.  If @wq is non-reentrant and @work
                 * was previously on a different cpu, it might still
                 * be running there, in which case the work needs to
                 * be queued on that cpu to guarantee non-reentrance.
                 */
                gcwq = get_gcwq(cpu);
                if (wq->flags & WQ_NON_REENTRANT &&
                    (last_gcwq = get_work_gcwq(work)) && last_gcwq != gcwq) {
                        struct worker *worker;

                        spin_lock_irqsave(&last_gcwq->lock, flags);

                        worker = find_worker_executing_work(last_gcwq, work);

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

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

        BUG_ON(!list_empty(&work->entry));

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

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

        insert_work(cwq, work, worklist, work_flags);

        spin_unlock_irqrestore(&gcwq->lock, flags);
}

/**
 * queue_work - queue work on a workqueue
 * @wq: workqueue to use
 * @work: work to queue
 *
 * Returns 0 if @work was already on a queue, non-zero otherwise.
 *
 * We queue the work to the CPU on which it was submitted, but if the CPU dies
 * it can be processed by another CPU.
 */
int queue_work(struct workqueue_struct *wq, struct work_struct *work)
{
        int ret;

        ret = queue_work_on(get_cpu(), wq, work);
        put_cpu();

        return ret;
}
EXPORT_SYMBOL_GPL(queue_work);

/**
 * queue_work_on - queue work on specific cpu
 * @cpu: CPU number to execute work on
 * @wq: workqueue to use
 * @work: work to queue
 *
 * Returns 0 if @work was already on a queue, non-zero otherwise.
 *
 * We queue the work to a specific CPU, the caller must ensure it
 * can't go away.
 */
int
queue_work_on(int cpu, struct workqueue_struct *wq, struct work_struct *work)
{
        int ret = 0;

        if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
                __queue_work(cpu, wq, work);
                ret = 1;
        }
        return ret;
}
EXPORT_SYMBOL_GPL(queue_work_on);

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

        __queue_work(smp_processor_id(), cwq->wq, &dwork->work);
}

/**
 * queue_delayed_work - queue work on a workqueue after delay
 * @wq: workqueue to use
 * @dwork: delayable work to queue
 * @delay: number of jiffies to wait before queueing
 *
 * Returns 0 if @work was already on a queue, non-zero otherwise.
 */
int queue_delayed_work(struct workqueue_struct *wq,
                        struct delayed_work *dwork, unsigned long delay)
{
        if (delay == 0)
                return queue_work(wq, &dwork->work);

        return queue_delayed_work_on(-1, wq, dwork, delay);
}
EXPORT_SYMBOL_GPL(queue_delayed_work);

/**
 * 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 0 if @work was already on a queue, non-zero otherwise.
 */
int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
                        struct delayed_work *dwork, unsigned long delay)
{
        int ret = 0;
        struct timer_list *timer = &dwork->timer;
        struct work_struct *work = &dwork->work;

        if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
                unsigned int lcpu;

                BUG_ON(timer_pending(timer));
                BUG_ON(!list_empty(&work->entry));

                timer_stats_timer_set_start_info(&dwork->timer);

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

                        if (gcwq && gcwq->cpu != WORK_CPU_UNBOUND)
                                lcpu = gcwq->cpu;
                        else
                                lcpu = raw_smp_processor_id();
                } else
                        lcpu = WORK_CPU_UNBOUND;

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

                timer->expires = jiffies + delay;
                timer->data = (unsigned long)dwork;
                timer->function = delayed_work_timer_fn;

                if (unlikely(cpu >= 0))
                        add_timer_on(timer, cpu);
                else
                        add_timer(timer);
                ret = 1;
        }
        return ret;
}
EXPORT_SYMBOL_GPL(queue_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(gcwq->lock).
 */
static void worker_enter_idle(struct worker *worker)
{
        struct global_cwq *gcwq = worker->gcwq;

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

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

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

        if (likely(!(worker->flags & WORKER_ROGUE))) {
                if (too_many_workers(gcwq) && !timer_pending(&gcwq->idle_timer))
                        mod_timer(&gcwq->idle_timer,
                                  jiffies + IDLE_WORKER_TIMEOUT);
        } else
                wake_up_all(&gcwq->trustee_wait);

        /* sanity check nr_running */
        WARN_ON_ONCE(gcwq->nr_workers == gcwq->nr_idle &&
                     atomic_read(get_gcwq_nr_running(gcwq->cpu)));
}

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

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

/**
 * worker_maybe_bind_and_lock - bind worker to its cpu if possible and lock gcwq
 * @worker: self
 *
 * 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 rogue 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 gcwq may be
 * [dis]associated in the meantime.
 *
 * This function tries set_cpus_allowed() and locks gcwq and verifies
 * the binding against GCWQ_DISASSOCIATED which is set during
 * CPU_DYING 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 gcwq->lock
 * held.
 *
 * RETURNS:
 * %true if the associated gcwq is online (@worker is successfully
 * bound), %false if offline.
 */
static bool worker_maybe_bind_and_lock(struct worker *worker)
__acquires(&gcwq->lock)
{
        struct global_cwq *gcwq = worker->gcwq;
        struct task_struct *task = worker->task;

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

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

                /* CPU has come up inbetween, retry migration */
                cpu_relax();
        }
}

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

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

        spin_unlock_irq(&gcwq->lock);
}

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

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

/**
 * create_worker - create a new workqueue worker
 * @gcwq: gcwq the new worker will belong to
 * @bind: whether to set affinity to @cpu or not
 *
 * Create a new worker which is bound to @gcwq.  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 global_cwq *gcwq, bool bind)
{
        bool on_unbound_cpu = gcwq->cpu == WORK_CPU_UNBOUND;
        struct worker *worker = NULL;
        int id = -1;

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

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

        worker->gcwq = gcwq;
        worker->id = id;

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

        /*
         * A rogue worker will become a regular one if CPU comes
         * online later on.  Make sure every worker has
         * PF_THREAD_BOUND set.
         */
        if (bind && !on_unbound_cpu)
                kthread_bind(worker->task, gcwq->cpu);
        else {
                worker->task->flags |= PF_THREAD_BOUND;
                if (on_unbound_cpu)
                        worker->flags |= WORKER_UNBOUND;
        }

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

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

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

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

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

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

        spin_unlock_irq(&gcwq->lock);

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

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

static void idle_worker_timeout(unsigned long __gcwq)
{
        struct global_cwq *gcwq = (void *)__gcwq;

        spin_lock_irq(&gcwq->lock);

        if (too_many_workers(gcwq)) {
                struct worker *worker;
                unsigned long expires;

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

                if (time_before(jiffies, expires))
                        mod_timer(&gcwq->idle_timer, expires);
                else {
                        /* it's been idle for too long, wake up manager */
                        gcwq->flags |= GCWQ_MANAGE_WORKERS;
                        wake_up_worker(gcwq);
                }
        }

        spin_unlock_irq(&gcwq->lock);
}

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

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

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

static void gcwq_mayday_timeout(unsigned long __gcwq)
{
        struct global_cwq *gcwq = (void *)__gcwq;
        struct work_struct *work;

        spin_lock_irq(&gcwq->lock);

        if (need_to_create_worker(gcwq)) {
                /*
                 * 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, &gcwq->worklist, entry)
                        send_mayday(work);
        }

        spin_unlock_irq(&gcwq->lock);

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

/**
 * maybe_create_worker - create a new worker if necessary
 * @gcwq: gcwq to create a new worker for
 *
 * Create a new worker for @gcwq if necessary.  @gcwq 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 @gcwq 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(gcwq->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 gcwq->lock stayed locked, true
 * otherwise.
 */
static bool maybe_create_worker(struct global_cwq *gcwq)
__releases(&gcwq->lock)
__acquires(&gcwq->lock)
{
        if (!need_to_create_worker(gcwq))
                return false;
restart:
        spin_unlock_irq(&gcwq->lock);

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

        while (true) {
                struct worker *worker;

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

                if (!need_to_create_worker(gcwq))
                        break;

                __set_current_state(TASK_INTERRUPTIBLE);
                schedule_timeout(CREATE_COOLDOWN);

                if (!need_to_create_worker(gcwq))
                        break;
        }

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

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

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

                worker = list_entry(gcwq->idle_list.prev, struct worker, entry);
                expires = worker->last_active + IDLE_WORKER_TIMEOUT;

                if (time_before(jiffies, expires)) {
                        mod_timer(&gcwq->idle_timer, expires);
                        break;
                }

                destroy_worker(worker);
                ret = true;
        }

        return ret;
}

/**
 * manage_workers - manage worker pool
 * @worker: self
 *
 * Assume the manager role and manage gcwq worker pool @worker belongs
 * to.  At any given time, there can be only zero or one manager per
 * gcwq.  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(gcwq->lock) which may be released and regrabbed
 * multiple times.  Does GFP_KERNEL allocations.
 *
 * RETURNS:
 * false if no action was taken and gcwq->lock stayed locked, true if
 * some action was taken.
 */
static bool manage_workers(struct worker *worker)
{
        struct global_cwq *gcwq = worker->gcwq;
        bool ret = false;

        if (gcwq->flags & GCWQ_MANAGING_WORKERS)
                return ret;

        gcwq->flags &= ~GCWQ_MANAGE_WORKERS;
        gcwq->flags |= GCWQ_MANAGING_WORKERS;

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

        gcwq->flags &= ~GCWQ_MANAGING_WORKERS;

        /*
         * The trustee might be waiting to take over the manager
         * position, tell it we're done.
         */
        if (unlikely(gcwq->trustee))
                wake_up_all(&gcwq->trustee_wait);

        return ret;
}

/**
 * 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(gcwq->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;
}

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

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

/**
 * cwq_dec_nr_in_flight - decrement cwq's nr_in_flight
 * @cwq: cwq of interest
 * @color: color of work which left the queue
 * @delayed: for a delayed work
 *
 * A work either has completed or is removed from pending queue,
 * decrement nr_in_flight of its cwq and handle workqueue flushing.
 *
 * CONTEXT:
 * spin_lock_irq(gcwq->lock).
 */
static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color,
                                 bool delayed)
{
        /* ignore uncolored works */
        if (color == WORK_NO_COLOR)
                return;

        cwq->nr_in_flight[color]--;

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

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

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

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

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

/**
 * 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(gcwq->lock) which is released and regrabbed.
 */
static void process_one_work(struct worker *worker, struct work_struct *work)
__releases(&gcwq->lock)
__acquires(&gcwq->lock)
{
        struct cpu_workqueue_struct *cwq = get_work_cwq(work);
        struct global_cwq *gcwq = cwq->gcwq;
        struct hlist_head *bwh = busy_worker_head(gcwq, work);
        bool cpu_intensive = cwq->wq->flags & WQ_CPU_INTENSIVE;
        work_func_t f = work->func;
        int work_color;
        struct worker *collision;
#ifdef CONFIG_LOCKDEP
        /*
         * It is permissible to free the struct work_struct from
         * inside the function that is called from it, this we need to
         * take into account for lockdep too.  To avoid bogus "held
         * lock freed" warnings as well as problems when looking into
         * work->lockdep_map, make a copy and use that here.
         */
        struct lockdep_map lockdep_map = work->lockdep_map;
#endif
        /*
         * A single work shouldn't be executed concurrently by
         * multiple workers on a single cpu.  Check whether anyone is
         * already processing the work.  If so, defer the work to the
         * currently executing one.
         */
        collision = __find_worker_executing_work(gcwq, bwh, work);
        if (unlikely(collision)) {
                move_linked_works(work, &collision->scheduled, NULL);
                return;
        }

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

        /* record the current cpu number in the work data and dequeue */
        set_work_cpu(work, gcwq->cpu);
        list_del_init(&work->entry);

        /*
         * If HIGHPRI_PENDING, check the next work, and, if HIGHPRI,
         * wake up another worker; otherwise, clear HIGHPRI_PENDING.
         */
        if (unlikely(gcwq->flags & GCWQ_HIGHPRI_PENDING)) {
                struct work_struct *nwork = list_first_entry(&gcwq->worklist,
                                                struct work_struct, entry);

                if (!list_empty(&gcwq->worklist) &&
                    get_work_cwq(nwork)->wq->flags & WQ_HIGHPRI)
                        wake_up_worker(gcwq);
                else
                        gcwq->flags &= ~GCWQ_HIGHPRI_PENDING;
        }

        /*
         * 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);

        spin_unlock_irq(&gcwq->lock);

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

        if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
                printk(KERN_ERR "BUG: workqueue leaked lock or atomic: "
                       "%s/0x%08x/%d\n",
                       current->comm, preempt_count(), task_pid_nr(current));
                printk(KERN_ERR "    last function: ");
                print_symbol("%s\n", (unsigned long)f);
                debug_show_held_locks(current);
                dump_stack();
        }

        spin_lock_irq(&gcwq->lock);

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

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

/**
 * 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(gcwq->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 gcwq worker thread function.  There's a single dynamic pool of
 * these per each cpu.  These workers process all works regardless of
 * their specific target workqueue.  The only exception is works 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 global_cwq *gcwq = worker->gcwq;

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

        /* DIE can be set only while we're idle, checking here is enough */
        if (worker->flags & WORKER_DIE) {
                spin_unlock_irq(&gcwq->lock);
                worker->task->flags &= ~PF_WQ_WORKER;
                return 0;
        }

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

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

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

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

        do {
                struct work_struct *work =
                        list_first_entry(&gcwq->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(gcwq));

        worker_set_flags(worker, WORKER_PREP, false);
sleep:
        if (unlikely(need_to_manage_workers(gcwq)) && manage_workers(worker))
                goto recheck;

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

/**
 * rescuer_thread - the rescuer thread function
 * @__wq: the associated workqueue
 *
 * Workqueue rescuer thread function.  There's one rescuer for each
 * workqueue which has WQ_RESCUER set.
 *
 * Regular work processing on a gcwq 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 gcwq summons rescuers of all
 * workqueues which have works queued on the gcwq and let them process
 * those works so that forward progress can be guaranteed.
 *
 * This should happen rarely.
 */
static int rescuer_thread(void *__wq)
{
        struct workqueue_struct *wq = __wq;
        struct worker *rescuer = wq->rescuer;
        struct list_head *scheduled = &rescuer->scheduled;
        bool is_unbound = wq->flags & WQ_UNBOUND;
        unsigned int cpu;

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

        if (kthread_should_stop())
                return 0;

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

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

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

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

                process_scheduled_works(rescuer);
                spin_unlock_irq(&gcwq->lock);
        }

        schedule();
        goto repeat;
}

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

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

/**
 * insert_wq_barrier - insert a barrier work
 * @cwq: cwq 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 cwq from @target.
 *
 * CONTEXT:
 * spin_lock_irq(gcwq->lock).
 */
static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
                              struct wq_barrier *barr,
                              struct work_struct *target, struct worker *worker)
{
        struct list_head *head;
        unsigned int linked = 0;

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

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

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

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

/**
 * flush_workqueue_prep_cwqs - prepare cwqs 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 cwqs for workqueue flushing.
 *
 * If @flush_color is non-negative, flush_color on all cwqs should be
 * -1.  If no cwq has in-flight commands at the specified color, all
 * cwq->flush_color's stay at -1 and %false is returned.  If any cwq
 * has in flight commands, its cwq->flush_color is set to
 * @flush_color, @wq->nr_cwqs_to_flush is updated accordingly, cwq
 * 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 cwqs should have the same
 * work_color which is previous to @work_color and all will be
 * advanced to @work_color.
 *
 * CONTEXT:
 * mutex_lock(wq->flush_mutex).
 *
 * RETURNS:
 * %true if @flush_color >= 0 and there's something to flush.  %false
 * otherwise.
 */
static bool flush_workqueue_prep_cwqs(struct workqueue_struct *wq,
                                      int flush_color, int work_color)
{
        bool wait = false;
        unsigned int cpu;

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

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

                spin_lock_irq(&gcwq->lock);

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

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

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

                spin_unlock_irq(&gcwq->lock);
        }

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

        return wait;
}

/**
 * flush_workqueue - ensure that any scheduled work has run to completion.
 * @wq: workqueue to flush
 *
 * Forces execution of the workqueue and blocks until its completion.
 * This is typically used in driver shutdown handlers.
 *
 * We sleep until all works which were queued on entry have been handled,
 * but we are 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->flush_mutex);

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

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

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

                        wq->first_flusher = &this_flusher;

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

        mutex_unlock(&wq->flush_mutex);

        wait_for_completion(&this_flusher.done);

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

        mutex_lock(&wq->flush_mutex);

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

        wq->first_flusher = NULL;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        lock_map_acquire(&cwq->wq->lockdep_map);
        lock_map_release(&cwq->wq->lockdep_map);
        return true;
already_gone:
        spin_unlock_irq(&gcwq->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.  This function considers
 * only the last queueing instance of @work.  If @work has been
 * enqueued across different CPUs on a non-reentrant workqueue or on
 * multiple workqueues, @work might still be executing on return on
 * some of the CPUs from earlier queueing.
 *
 * If @work was queued only on a non-reentrant, ordered or unbound
 * workqueue, @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;

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

static bool wait_on_cpu_work(struct global_cwq *gcwq, struct work_struct *work)
{
        struct wq_barrier barr;
        struct worker *worker;

        spin_lock_irq(&gcwq->lock);

        worker = find_worker_executing_work(gcwq, work);
        if (unlikely(worker))
                insert_wq_barrier(worker->current_cwq, &barr, work, worker);

        spin_unlock_irq(&gcwq->lock);

        if (unlikely(worker)) {
                wait_for_completion(&barr.done);
                destroy_work_on_stack(&barr.work);
                return true;
        } else
                return false;
}

static bool wait_on_work(struct work_struct *work)
{
        bool ret = false;
        int cpu;

        might_sleep();

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

        for_each_gcwq_cpu(cpu)
                ret |= wait_on_cpu_work(get_gcwq(cpu), work);
        return ret;
}

/**
 * flush_work_sync - wait until a work has finished execution
 * @work: the work to flush
 *
 * Wait until @work has finished execution.  On return, it's
 * guaranteed that all queueing instances of @work which happened
 * before this function is called are finished.  In other words, if
 * @work hasn't been requeued since this function was called, @work is
 * guaranteed to be idle on return.
 *
 * RETURNS:
 * %true if flush_work_sync() waited for the work to finish execution,
 * %false if it was already idle.
 */
bool flush_work_sync(struct work_struct *work)
{
        struct wq_barrier barr;
        bool pending, waited;

        /* we'll wait for executions separately, queue barr only if pending */
        pending = start_flush_work(work, &barr, false);

        /* wait for executions to finish */
        waited = wait_on_work(work);

        /* wait for the pending one */
        if (pending) {
                wait_for_completion(&barr.done);
                destroy_work_on_stack(&barr.work);
        }

        return pending || waited;
}
EXPORT_SYMBOL_GPL(flush_work_sync);

/*
 * Upon a successful return (>= 0), the caller "owns" WORK_STRUCT_PENDING bit,
 * so this work can't be re-armed in any way.
 */
static int try_to_grab_pending(struct work_struct *work)
{
        struct global_cwq *gcwq;
        int ret = -1;

        if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)))
                return 0;

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

        spin_lock_irq(&gcwq->lock);
        if (!list_empty(&work->entry)) {
                /*
                 * This work is queued, but perhaps we locked the wrong gcwq.
                 * In that case we must see the new value after rmb(), see
                 * insert_work()->wmb().
                 */
                smp_rmb();
                if (gcwq == get_work_gcwq(work)) {
                        debug_work_deactivate(work);
                        list_del_init(&work->entry);
                        cwq_dec_nr_in_flight(get_work_cwq(work),
                                get_work_color(work),
                                *work_data_bits(work) & WORK_STRUCT_DELAYED);
                        ret = 1;
                }
        }
        spin_unlock_irq(&gcwq->lock);

        return ret;
}

static bool __cancel_work_timer(struct work_struct *work,
                                struct timer_list* timer)
{
        int ret;

        do {
                ret = (timer && likely(del_timer(timer)));
                if (!ret)
                        ret = try_to_grab_pending(work);
                wait_on_work(work);
        } while (unlikely(ret < 0));

        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, NULL);
}
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)
{
        if (del_timer_sync(&dwork->timer))
                __queue_work(raw_smp_processor_id(),
                             get_work_cwq(&dwork->work)->wq, &dwork->work);
        return flush_work(&dwork->work);
}
EXPORT_SYMBOL(flush_delayed_work);

/**
 * flush_delayed_work_sync - wait for a dwork to finish
 * @dwork: the delayed work to flush
 *
 * Delayed timer is cancelled and the pending work is queued for
 * execution immediately.  Other than timer handling, its behavior
 * is identical to flush_work_sync().
 *
 * RETURNS:
 * %true if flush_work_sync() waited for the work to finish execution,
 * %false if it was already idle.
 */
bool flush_delayed_work_sync(struct delayed_work *dwork)
{
        if (del_timer_sync(&dwork->timer))
                __queue_work(raw_smp_processor_id(),
                             get_work_cwq(&dwork->work)->wq, &dwork->work);
        return flush_work_sync(&dwork->work);
}
EXPORT_SYMBOL(flush_delayed_work_sync);

/**
 * 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, &dwork->timer);
}
EXPORT_SYMBOL(cancel_delayed_work_sync);

/**
 * schedule_work - put work task in global workqueue
 * @work: job to be done
 *
 * Returns zero if @work was already on the kernel-global workqueue and
 * non-zero otherwise.
 *
 * This puts a job in the kernel-global workqueue if it was not already
 * queued and leaves it in the same position on the kernel-global
 * workqueue otherwise.
 */
int schedule_work(struct work_struct *work)
{
        return queue_work(system_wq, work);
}
EXPORT_SYMBOL(schedule_work);

/*
 * schedule_work_on - put work task on a specific cpu
 * @cpu: cpu to put the work task on
 * @work: job to be done
 *
 * This puts a job on a specific cpu
 */
int schedule_work_on(int cpu, struct work_struct *work)
{
        return queue_work_on(cpu, system_wq, work);
}
EXPORT_SYMBOL(schedule_work_on);

/**
 * schedule_delayed_work - put work task in global workqueue after delay
 * @dwork: job to be done
 * @delay: number of jiffies to wait or 0 for immediate execution
 *
 * After waiting for a given time this puts a job in the kernel-global
 * workqueue.
 */
int schedule_delayed_work(struct delayed_work *dwork,
                                        unsigned long delay)
{
        return queue_delayed_work(system_wq, dwork, delay);
}
EXPORT_SYMBOL(schedule_delayed_work);

/**
 * schedule_delayed_work_on - queue work in global workqueue on CPU after delay
 * @cpu: cpu to use
 * @dwork: job to be done
 * @delay: number of jiffies to wait
 *
 * After waiting for a given time this puts a job in the kernel-global
 * workqueue on the specified CPU.
 */
int schedule_delayed_work_on(int cpu,
                        struct delayed_work *dwork, unsigned long delay)
{
        return queue_delayed_work_on(cpu, system_wq, dwork, delay);
}
EXPORT_SYMBOL(schedule_delayed_work_on);

/**
 * 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);

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

static int alloc_cwqs(struct workqueue_struct *wq)
{
        /*
         * cwqs are forced aligned according to WORK_STRUCT_FLAG_BITS.
         * Make sure that the alignment isn't lower than that of
         * unsigned long long.
         */
        const size_t size = sizeof(struct cpu_workqueue_struct);
        const size_t align = max_t(size_t, 1 << WORK_STRUCT_FLAG_BITS,
                                   __alignof__(unsigned long long));
#ifdef CONFIG_SMP
        bool percpu = !(wq->flags & WQ_UNBOUND);
#else
        bool percpu = false;
#endif

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

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

        /* just in case, make sure it's actually aligned
         * - this is affected by PERCPU() alignment in vmlinux.lds.S
         */
        BUG_ON(!IS_ALIGNED(wq->cpu_wq.v, align));
        return wq->cpu_wq.v ? 0 : -ENOMEM;
}

static void free_cwqs(struct workqueue_struct *wq)
{
#ifdef CONFIG_SMP
        bool percpu = !(wq->flags & WQ_UNBOUND);
#else
        bool percpu = false;
#endif

        if (percpu)
                free_percpu(wq->cpu_wq.pcpu);
        else if (wq->cpu_wq.single) {
                /* the pointer to free is stored right after the cwq */
                kfree(*(void **)(wq->cpu_wq.single + 1));
        }
}

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

        if (max_active < 1 || max_active > lim)
                printk(KERN_WARNING "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 *name,
                                               unsigned int flags,
                                               int max_active,
                                               struct lock_class_key *key,
                                               const char *lock_name)
{
        struct workqueue_struct *wq;
        unsigned int cpu;

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

        /*
         * Unbound workqueues aren't concurrency managed and should be
         * dispatched to workers immediately.
         */
        if (flags & WQ_UNBOUND)
                flags |= WQ_HIGHPRI;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        spin_unlock(&workqueue_lock);

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

/**
 * 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)
{
        unsigned int cpu;

        wq->flags |= WQ_DYING;
        flush_workqueue(wq);

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

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

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

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

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

/**
 * 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)
{
        unsigned int cpu;

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

        spin_lock(&workqueue_lock);

        wq->saved_max_active = max_active;

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

                spin_lock_irq(&gcwq->lock);

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

                spin_unlock_irq(&gcwq->lock);
        }

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

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

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

/**
 * work_cpu - return the last known associated cpu for @work
 * @work: the work of interest
 *
 * RETURNS:
 * CPU number if @work was ever queued.  WORK_CPU_NONE otherwise.
 */
unsigned int work_cpu(struct work_struct *work)
{
        struct global_cwq *gcwq = get_work_gcwq(work);

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

/**
 * 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.
 * Especially for reentrant wqs, the pending state might hide the
 * running state.
 *
 * RETURNS:
 * OR'd bitmask of WORK_BUSY_* bits.
 */
unsigned int work_busy(struct work_struct *work)
{
        struct global_cwq *gcwq = get_work_gcwq(work);
        unsigned long flags;
        unsigned int ret = 0;

        if (!gcwq)
                return false;

        spin_lock_irqsave(&gcwq->lock, flags);

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

        spin_unlock_irqrestore(&gcwq->lock, flags);

        return ret;
}
EXPORT_SYMBOL_GPL(work_busy);

/*
 * CPU hotplug.
 *
 * There are two challenges in supporting CPU hotplug.  Firstly, there
 * are a lot of assumptions on strong associations among work, cwq and
 * gcwq which make migrating pending and scheduled works very
 * difficult to implement without impacting hot paths.  Secondly,
 * gcwqs serve mix of short, long and very long running works making
 * blocked draining impractical.
 *
 * This is solved by allowing a gcwq to be detached from CPU, running
 * it with unbound (rogue) workers and allowing it to be reattached
 * later if the cpu comes back online.  A separate thread is created
 * to govern a gcwq in such state and is called the trustee of the
 * gcwq.
 *
 * Trustee states and their descriptions.
 *
 * START        Command state used on startup.  On CPU_DOWN_PREPARE, a
 *              new trustee is started with this state.
 *
 * IN_CHARGE    Once started, trustee will enter this state after
 *              assuming the manager role and making all existing
 *              workers rogue.  DOWN_PREPARE waits for trustee to
 *              enter this state.  After reaching IN_CHARGE, trustee
 *              tries to execute the pending worklist until it's empty
 *              and the state is set to BUTCHER, or the state is set
 *              to RELEASE.
 *
 * BUTCHER      Command state which is set by the cpu callback after
 *              the cpu has went down.  Once this state is set trustee
 *              knows that there will be no new works on the worklist
 *              and once the worklist is empty it can proceed to
 *              killing idle workers.
 *
 * RELEASE      Command state which is set by the cpu callback if the
 *              cpu down has been canceled or it has come online
 *              again.  After recognizing this state, trustee stops
 *              trying to drain or butcher and clears ROGUE, rebinds
 *              all remaining workers back to the cpu and releases
 *              manager role.
 *
 * DONE         Trustee will enter this state after BUTCHER or RELEASE
 *              is complete.
 *
 *          trustee                 CPU                draining
 *         took over                down               complete
 * START -----------> IN_CHARGE -----------> BUTCHER -----------> DONE
 *                        |                     |                  ^
 *                        | CPU is back online  v   return workers |
 *                         ----------------> RELEASE --------------
 */

/**
 * trustee_wait_event_timeout - timed event wait for trustee
 * @cond: condition to wait for
 * @timeout: timeout in jiffies
 *
 * wait_event_timeout() for trustee to use.  Handles locking and
 * checks for RELEASE request.
 *
 * CONTEXT:
 * spin_lock_irq(gcwq->lock) which may be released and regrabbed
 * multiple times.  To be used by trustee.
 *
 * RETURNS:
 * Positive indicating left time if @cond is satisfied, 0 if timed
 * out, -1 if canceled.
 */
#define trustee_wait_event_timeout(cond, timeout) ({                    \
        long __ret = (timeout);                                         \
        while (!((cond) || (gcwq->trustee_state == TRUSTEE_RELEASE)) && \
               __ret) {                                                 \
                spin_unlock_irq(&gcwq->lock);                           \
                __wait_event_timeout(gcwq->trustee_wait, (cond) ||      \
                        (gcwq->trustee_state == TRUSTEE_RELEASE),       \
                        __ret);                                         \
                spin_lock_irq(&gcwq->lock);                             \
        }                                                               \
        gcwq->trustee_state == TRUSTEE_RELEASE ? -1 : (__ret);          \
})

/**
 * trustee_wait_event - event wait for trustee
 * @cond: condition to wait for
 *
 * wait_event() for trustee to use.  Automatically handles locking and
 * checks for CANCEL request.
 *
 * CONTEXT:
 * spin_lock_irq(gcwq->lock) which may be released and regrabbed
 * multiple times.  To be used by trustee.
 *
 * RETURNS:
 * 0 if @cond is satisfied, -1 if canceled.
 */
#define trustee_wait_event(cond) ({                                     \
        long __ret1;                                                    \
        __ret1 = trustee_wait_event_timeout(cond, MAX_SCHEDULE_TIMEOUT);\
        __ret1 < 0 ? -1 : 0;                                            \
})

static int __cpuinit trustee_thread(void *__gcwq)
{
        struct global_cwq *gcwq = __gcwq;
        struct worker *worker;
        struct work_struct *work;
        struct hlist_node *pos;
        long rc;
        int i;

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

        spin_lock_irq(&gcwq->lock);
        /*
         * Claim the manager position and make all workers rogue.
         * Trustee must be bound to the target cpu and can't be
         * cancelled.
         */
        BUG_ON(gcwq->cpu != smp_processor_id());
        rc = trustee_wait_event(!(gcwq->flags & GCWQ_MANAGING_WORKERS));
        BUG_ON(rc < 0);

        gcwq->flags |= GCWQ_MANAGING_WORKERS;

        list_for_each_entry(worker, &gcwq->idle_list, entry)
                worker->flags |= WORKER_ROGUE;

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

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

        /*
         * 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.
         */
        atomic_set(get_gcwq_nr_running(gcwq->cpu), 0);

        spin_unlock_irq(&gcwq->lock);
        del_timer_sync(&gcwq->idle_timer);
        spin_lock_irq(&gcwq->lock);

        /*
         * We're now in charge.  Notify and proceed to drain.  We need
         * to keep the gcwq running during the whole CPU down
         * procedure as other cpu hotunplug callbacks may need to
         * flush currently running tasks.
         */
        gcwq->trustee_state = TRUSTEE_IN_CHARGE;
        wake_up_all(&gcwq->trustee_wait);

        /*
         * The original cpu is in the process of dying and may go away
         * anytime now.  When that happens, we and all workers would
         * be migrated to other cpus.  Try draining any left work.  We
         * want to get it over with ASAP - spam rescuers, wake up as
         * many idlers as necessary and create new ones till the
         * worklist is empty.  Note that if the gcwq is frozen, there
         * may be frozen works in freezeable cwqs.  Don't declare
         * completion while frozen.
         */
        while (gcwq->nr_workers != gcwq->nr_idle ||
               gcwq->flags & GCWQ_FREEZING ||
               gcwq->trustee_state == TRUSTEE_IN_CHARGE) {
                int nr_works = 0;

                list_for_each_entry(work, &gcwq->worklist, entry) {
                        send_mayday(work);
                        nr_works++;
                }

                list_for_each_entry(worker, &gcwq->idle_list, entry) {
                        if (!nr_works--)
                                break;
                        wake_up_process(worker->task);
                }

                if (need_to_create_worker(gcwq)) {
                        spin_unlock_irq(&gcwq->lock);
                        worker = create_worker(gcwq, false);
                        spin_lock_irq(&gcwq->lock);
                        if (worker) {
                                worker->flags |= WORKER_ROGUE;
                                start_worker(worker);
                        }
                }

                /* give a breather */
                if (trustee_wait_event_timeout(false, TRUSTEE_COOLDOWN) < 0)
                        break;
        }

        /*
         * Either all works have been scheduled and cpu is down, or
         * cpu down has already been canceled.  Wait for and butcher
         * all workers till we're canceled.
         */
        do {
                rc = trustee_wait_event(!list_empty(&gcwq->idle_list));
                while (!list_empty(&gcwq->idle_list))
                        destroy_worker(list_first_entry(&gcwq->idle_list,
                                                        struct worker, entry));
        } while (gcwq->nr_workers && rc >= 0);

        /*
         * At this point, either draining has completed and no worker
         * is left, or cpu down has been canceled or the cpu is being
         * brought back up.  There shouldn't be any idle one left.
         * Tell the remaining busy ones to rebind once it finishes the
         * currently scheduled works by scheduling the rebind_work.
         */
        WARN_ON(!list_empty(&gcwq->idle_list));

        for_each_busy_worker(worker, i, pos, gcwq) {
                struct work_struct *rebind_work = &worker->rebind_work;

                /*
                 * Rebind_work may race with future cpu hotplug
                 * operations.  Use a separate flag to mark that
                 * rebinding is scheduled.
                 */
                worker->flags |= WORKER_REBIND;
                worker->flags &= ~WORKER_ROGUE;

                /* queue rebind_work, wq doesn't matter, use the default one */
                if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
                                     work_data_bits(rebind_work)))
                        continue;

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

        /* relinquish manager role */
        gcwq->flags &= ~GCWQ_MANAGING_WORKERS;

        /* notify completion */
        gcwq->trustee = NULL;
        gcwq->trustee_state = TRUSTEE_DONE;
        wake_up_all(&gcwq->trustee_wait);
        spin_unlock_irq(&gcwq->lock);
        return 0;
}

/**
 * wait_trustee_state - wait for trustee to enter the specified state
 * @gcwq: gcwq the trustee of interest belongs to
 * @state: target state to wait for
 *
 * Wait for the trustee to reach @state.  DONE is already matched.
 *
 * CONTEXT:
 * spin_lock_irq(gcwq->lock) which may be released and regrabbed
 * multiple times.  To be used by cpu_callback.
 */
static void __cpuinit wait_trustee_state(struct global_cwq *gcwq, int state)
__releases(&gcwq->lock)
__acquires(&gcwq->lock)
{
        if (!(gcwq->trustee_state == state ||
              gcwq->trustee_state == TRUSTEE_DONE)) {
                spin_unlock_irq(&gcwq->lock);
                __wait_event(gcwq->trustee_wait,
                             gcwq->trustee_state == state ||
                             gcwq->trustee_state == TRUSTEE_DONE);
                spin_lock_irq(&gcwq->lock);
        }
}

static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
                                                unsigned long action,
                                                void *hcpu)
{
        unsigned int cpu = (unsigned long)hcpu;
        struct global_cwq *gcwq = get_gcwq(cpu);
        struct task_struct *new_trustee = NULL;
        struct worker *uninitialized_var(new_worker);
        unsigned long flags;

        action &= ~CPU_TASKS_FROZEN;

        switch (action) {
        case CPU_DOWN_PREPARE:
                new_trustee = kthread_create(trustee_thread, gcwq,
                                             "workqueue_trustee/%d\n", cpu);
                if (IS_ERR(new_trustee))
                        return notifier_from_errno(PTR_ERR(new_trustee));
                kthread_bind(new_trustee, cpu);
                /* fall through */
        case CPU_UP_PREPARE:
                BUG_ON(gcwq->first_idle);
                new_worker = create_worker(gcwq, false);
                if (!new_worker) {
                        if (new_trustee)
                                kthread_stop(new_trustee);
                        return NOTIFY_BAD;
                }
        }

        /* some are called w/ irq disabled, don't disturb irq status */
        spin_lock_irqsave(&gcwq->lock, flags);

        switch (action) {
        case CPU_DOWN_PREPARE:
                /* initialize trustee and tell it to acquire the gcwq */
                BUG_ON(gcwq->trustee || gcwq->trustee_state != TRUSTEE_DONE);
                gcwq->trustee = new_trustee;
                gcwq->trustee_state = TRUSTEE_START;
                wake_up_process(gcwq->trustee);
                wait_trustee_state(gcwq, TRUSTEE_IN_CHARGE);
                /* fall through */
        case CPU_UP_PREPARE:
                BUG_ON(gcwq->first_idle);
                gcwq->first_idle = new_worker;
                break;

        case CPU_DYING:
                /*
                 * Before this, the trustee and 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'll all be diasporas.
                 */
                gcwq->flags |= GCWQ_DISASSOCIATED;
                break;

        case CPU_POST_DEAD:
                gcwq->trustee_state = TRUSTEE_BUTCHER;
                /* fall through */
        case CPU_UP_CANCELED:
                destroy_worker(gcwq->first_idle);
                gcwq->first_idle = NULL;
                break;

        case CPU_DOWN_FAILED:
        case CPU_ONLINE:
                gcwq->flags &= ~GCWQ_DISASSOCIATED;
                if (gcwq->trustee_state != TRUSTEE_DONE) {
                        gcwq->trustee_state = TRUSTEE_RELEASE;
                        wake_up_process(gcwq->trustee);
                        wait_trustee_state(gcwq, TRUSTEE_DONE);
                }

                /*
                 * Trustee is done and there might be no worker left.
                 * Put the first_idle in and request a real manager to
                 * take a look.
                 */
                spin_unlock_irq(&gcwq->lock);
                kthread_bind(gcwq->first_idle->task, cpu);
                spin_lock_irq(&gcwq->lock);
                gcwq->flags |= GCWQ_MANAGE_WORKERS;
                start_worker(gcwq->first_idle);
                gcwq->first_idle = NULL;
                break;
        }

        spin_unlock_irqrestore(&gcwq->lock, flags);

        return notifier_from_errno(0);
}

#ifdef CONFIG_SMP

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

static int do_work_for_cpu(void *_wfc)
{
        struct work_for_cpu *wfc = _wfc;
        wfc->ret = wfc->fn(wfc->arg);
        complete(&wfc->completion);
        return 0;
}

/**
 * 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(unsigned int cpu, long (*fn)(void *), void *arg)
{
        struct task_struct *sub_thread;
        struct work_for_cpu wfc = {
                .completion = COMPLETION_INITIALIZER_ONSTACK(wfc.completion),
                .fn = fn,
                .arg = arg,
        };

        sub_thread = kthread_create(do_work_for_cpu, &wfc, "work_for_cpu");
        if (IS_ERR(sub_thread))
                return PTR_ERR(sub_thread);
        kthread_bind(sub_thread, cpu);
        wake_up_process(sub_thread);
        wait_for_completion(&wfc.completion);
        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
 * freezeable workqueues will queue new works to their frozen_works
 * list instead of gcwq->worklist.
 *
 * CONTEXT:
 * Grabs and releases workqueue_lock and gcwq->lock's.
 */
void freeze_workqueues_begin(void)
{
        unsigned int cpu;

        spin_lock(&workqueue_lock);

        BUG_ON(workqueue_freezing);
        workqueue_freezing = true;

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

                spin_lock_irq(&gcwq->lock);

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

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

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

                spin_unlock_irq(&gcwq->lock);
        }

        spin_unlock(&workqueue_lock);
}

/**
 * freeze_workqueues_busy - are freezeable workqueues still busy?
 *
 * Check whether freezing is complete.  This function must be called
 * between freeze_workqueues_begin() and thaw_workqueues().
 *
 * CONTEXT:
 * Grabs and releases workqueue_lock.
 *
 * RETURNS:
 * %true if some freezeable workqueues are still busy.  %false if
 * freezing is complete.
 */
bool freeze_workqueues_busy(void)
{
        unsigned int cpu;
        bool busy = false;

        spin_lock(&workqueue_lock);

        BUG_ON(!workqueue_freezing);

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

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

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

/**
 * thaw_workqueues - thaw workqueues
 *
 * Thaw workqueues.  Normal queueing is restored and all collected
 * frozen works are transferred to their respective gcwq worklists.
 *
 * CONTEXT:
 * Grabs and releases workqueue_lock and gcwq->lock's.
 */
void thaw_workqueues(void)
{
        unsigned int cpu;

        spin_lock(&workqueue_lock);

        if (!workqueue_freezing)
                goto out_unlock;

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

                spin_lock_irq(&gcwq->lock);

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

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

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

                        /* restore max_active and repopulate worklist */
                        cwq->max_active = wq->saved_max_active;

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

                wake_up_worker(gcwq);

                spin_unlock_irq(&gcwq->lock);
        }

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

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

        cpu_notifier(workqueue_cpu_callback, CPU_PRI_WORKQUEUE);

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

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

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

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

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

                ida_init(&gcwq->worker_ida);

                gcwq->trustee_state = TRUSTEE_DONE;
                init_waitqueue_head(&gcwq->trustee_wait);
        }

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

                if (cpu != WORK_CPU_UNBOUND)
                        gcwq->flags &= ~GCWQ_DISASSOCIATED;
                worker = create_worker(gcwq, true);
                BUG_ON(!worker);
                spin_lock_irq(&gcwq->lock);
                start_worker(worker);
                spin_unlock_irq(&gcwq->lock);
        }

        system_wq = alloc_workqueue("events", 0, 0);
        system_long_wq = alloc_workqueue("events_long", 0, 0);
        system_nrt_wq = alloc_workqueue("events_nrt", WQ_NON_REENTRANT, 0);
        system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND,
                                            WQ_UNBOUND_MAX_ACTIVE);
        BUG_ON(!system_wq || !system_long_wq || !system_nrt_wq);
        return 0;
}
early_initcall(init_workqueues);