1 files changed, 833 insertions, 103 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 4c31fde092c6..0ad46523b423 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -34,17 +34,25 @@
 #include <linux/debug_locks.h>
 #include <linux/lockdep.h>
 #include <linux/idr.h>
-#include <linux/delay.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 */
 
         /* 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_NOT_RUNNING      = WORKER_PREP | WORKER_ROGUE | WORKER_REBIND,
 
         /* gcwq->trustee_state */
         TRUSTEE_START           = 0,            /* start */
@@ -57,7 +65,19 @@ enum {
         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,
 };
 
 /*
@@ -65,8 +85,16 @@ enum {
  *
  * I: Set during initialization and read-only afterwards.
  *
+ * 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.
+ *    While trustee is in charge, it's identical to L.
+ *
  * F: wq->flush_mutex protected.
  *
  * W: workqueue_lock protected.
@@ -74,6 +102,10 @@ enum {
 
 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 {
@@ -86,12 +118,17 @@ struct worker {
         struct list_head        scheduled;      /* L: scheduled works */
         struct task_struct      *task;          /* I: worker task */
         struct global_cwq       *gcwq;          /* I: the associated gcwq */
-        unsigned int            flags;          /* L: flags */
+        /* 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.
+ * 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 */
@@ -103,15 +140,19 @@ struct global_cwq {
         int                     nr_idle;        /* L: currently idle ones */
 
         /* workers are chained either in the idle_list or busy_hash */
-        struct list_head        idle_list;      /* L: list of idle workers */
+        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;
 
 /*
@@ -121,7 +162,6 @@ struct global_cwq {
  */
 struct cpu_workqueue_struct {
         struct global_cwq       *gcwq;          /* I: the associated gcwq */
-        struct worker           *worker;
         struct workqueue_struct *wq;            /* I: the owning workqueue */
         int                     work_color;     /* L: current color */
         int                     flush_color;    /* L: flushing color */
@@ -160,6 +200,9 @@ struct workqueue_struct {
 
         unsigned long           single_cpu;     /* cpu for single cpu wq */
 
+        cpumask_var_t           mayday_mask;    /* cpus requesting rescue */
+        struct worker           *rescuer;       /* I: rescue worker */
+
         int                     saved_max_active; /* I: saved cwq max_active */
         const char              *name;          /* I: workqueue name */
 #ifdef CONFIG_LOCKDEP
@@ -286,7 +329,13 @@ 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);
 
 static int worker_thread(void *__worker);
 
@@ -295,6 +344,11 @@ static struct global_cwq *get_gcwq(unsigned int cpu)
         return &per_cpu(global_cwq, cpu);
 }
 
+static atomic_t *get_gcwq_nr_running(unsigned int cpu)
+{
+        return &per_cpu(gcwq_nr_running, cpu);
+}
+
 static struct cpu_workqueue_struct *get_cwq(unsigned int cpu,
                                             struct workqueue_struct *wq)
 {
@@ -385,6 +439,63 @@ static struct global_cwq *get_work_gcwq(struct work_struct *work)
         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.
+ */
+
+/*
+ * Need to wake up a worker?  Called from anything but currently
+ * running workers.
+ */
+static bool need_more_worker(struct global_cwq *gcwq)
+{
+        atomic_t *nr_running = get_gcwq_nr_running(gcwq->cpu);
+
+        return !list_empty(&gcwq->worklist) && !atomic_read(nr_running);
+}
+
+/* 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;
+}
+
+/* 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)
 {
@@ -412,12 +523,77 @@ static void wake_up_worker(struct global_cwq *gcwq)
 }
 
 /**
- * worker_set_flags - set worker flags
+ * 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: worker to set flags for
  * @flags: flags to set
  * @wakeup: wakeup an idle worker if necessary
  *
- * Set @flags in @worker->flags.
+ * 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.
  *
  * LOCKING:
  * spin_lock_irq(gcwq->lock).
@@ -425,22 +601,49 @@ static void wake_up_worker(struct global_cwq *gcwq)
 static inline void worker_set_flags(struct worker *worker, unsigned int flags,
                                     bool wakeup)
 {
+        struct global_cwq *gcwq = worker->gcwq;
+
+        /*
+         * 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
+ * worker_clr_flags - clear worker flags and adjust nr_running accordingly
  * @worker: worker to set flags for
  * @flags: flags to clear
  *
- * Clear @flags in @worker->flags.
+ * Clear @flags in @worker->flags and adjust nr_running accordingly.
  *
  * LOCKING:
  * 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;
+
         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));
 }
 
 /**
@@ -540,6 +743,8 @@ 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);
 
@@ -550,7 +755,16 @@ static void insert_work(struct cpu_workqueue_struct *cwq,
         smp_wmb();
 
         list_add_tail(&work->entry, head);
-        wake_up_worker(cwq->gcwq);
+
+        /*
+         * 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 (!atomic_read(get_gcwq_nr_running(gcwq->cpu)))
+                wake_up_worker(gcwq);
 }
 
 /**
@@ -810,11 +1024,16 @@ static void worker_enter_idle(struct worker *worker)
 
         worker_set_flags(worker, WORKER_IDLE, false);
         gcwq->nr_idle++;
+        worker->last_active = jiffies;
 
         /* idle_list is LIFO */
         list_add(&worker->entry, &gcwq->idle_list);
 
-        if (unlikely(worker->flags & WORKER_ROGUE))
+        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);
 }
 
@@ -837,6 +1056,81 @@ static void worker_leave_idle(struct worker *worker)
         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)
+{
+        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.
+                 */
+                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;
@@ -845,6 +1139,9 @@ static struct worker *alloc_worker(void)
         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;
 }
@@ -963,6 +1260,220 @@ static void destroy_worker(struct worker *worker)
         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;
+
+        if (!(wq->flags & WQ_RESCUER))
+                return false;
+
+        /* mayday mayday mayday */
+        if (!cpumask_test_and_set_cpu(cwq->gcwq->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)
+{
+        if (!need_to_create_worker(gcwq))
+                return false;
+restart:
+        /* 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;
+
+                spin_unlock_irq(&gcwq->lock);
+
+                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;
+
+                spin_unlock_irq(&gcwq->lock);
+                __set_current_state(TASK_INTERRUPTIBLE);
+                schedule_timeout(CREATE_COOLDOWN);
+                spin_lock_irq(&gcwq->lock);
+                if (!need_to_create_worker(gcwq))
+                        break;
+        }
+
+        spin_unlock_irq(&gcwq->lock);
+        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
@@ -1169,24 +1680,39 @@ static void process_scheduled_works(struct worker *worker)
  * worker_thread - the worker thread function
  * @__worker: self
  *
- * The cwq worker thread function.
+ * 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.
@@ -1194,27 +1720,18 @@ recheck:
          */
         BUG_ON(!list_empty(&worker->scheduled));
 
-        while (!list_empty(&gcwq->worklist)) {
+        /*
+         * 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);
 
-                /*
-                 * The following is a rather inefficient way to close
-                 * race window against cpu hotplug operations.  Will
-                 * be replaced soon.
-                 */
-                if (unlikely(!(worker->flags & WORKER_ROGUE) &&
-                             !cpumask_equal(&worker->task->cpus_allowed,
-                                            get_cpu_mask(gcwq->cpu)))) {
-                        spin_unlock_irq(&gcwq->lock);
-                        set_cpus_allowed_ptr(worker->task,
-                                             get_cpu_mask(gcwq->cpu));
-                        cpu_relax();
-                        spin_lock_irq(&gcwq->lock);
-                        goto recheck;
-                }
-
                 if (likely(!(*work_data_bits(work) & WORK_STRUCT_LINKED))) {
                         /* optimization path, not strictly necessary */
                         process_one_work(worker, work);
@@ -1224,13 +1741,19 @@ recheck:
                         move_linked_works(work, &worker->scheduled, NULL);
                         process_scheduled_works(worker);
                 }
-        }
+        } while (keep_working(gcwq));
+
+        worker_set_flags(worker, WORKER_PREP, false);
 
+        if (unlikely(need_to_manage_workers(gcwq)) && manage_workers(worker))
+                goto recheck;
+sleep:
         /*
-         * gcwq->lock is held and there's no work to process, sleep.
-         * Workers are woken up only while holding gcwq->lock, so
-         * setting the current state before releasing gcwq->lock is
-         * enough to prevent losing any event.
+         * 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);
@@ -1239,6 +1762,68 @@ recheck:
         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;
+        unsigned int cpu;
+
+        set_user_nice(current, RESCUER_NICE_LEVEL);
+repeat:
+        set_current_state(TASK_INTERRUPTIBLE);
+
+        if (kthread_should_stop())
+                return 0;
+
+        for_each_cpu(cpu, wq->mayday_mask) {
+                struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
+                struct global_cwq *gcwq = cwq->gcwq;
+                struct work_struct *work, *n;
+
+                __set_current_state(TASK_RUNNING);
+                cpumask_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;
@@ -1998,7 +2583,6 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
                                                 const char *lock_name)
 {
         struct workqueue_struct *wq;
-        bool failed = false;
         unsigned int cpu;
 
         max_active = clamp_val(max_active, 1, INT_MAX);
@@ -2023,13 +2607,6 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
         lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
         INIT_LIST_HEAD(&wq->list);
 
-        cpu_maps_update_begin();
-        /*
-         * We must initialize cwqs for each possible cpu even if we
-         * are going to call destroy_workqueue() finally. Otherwise
-         * cpu_up() can hit the uninitialized cwq once we drop the
-         * lock.
-         */
         for_each_possible_cpu(cpu) {
                 struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
                 struct global_cwq *gcwq = get_gcwq(cpu);
@@ -2040,14 +2617,25 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
                 cwq->flush_color = -1;
                 cwq->max_active = max_active;
                 INIT_LIST_HEAD(&cwq->delayed_works);
+        }
 
-                if (failed)
-                        continue;
-                cwq->worker = create_worker(gcwq, cpu_online(cpu));
-                if (cwq->worker)
-                        start_worker(cwq->worker);
-                else
-                        failed = true;
+        if (flags & WQ_RESCUER) {
+                struct worker *rescuer;
+
+                if (!alloc_cpumask_var(&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;
+
+                wq->rescuer = rescuer;
+                rescuer->task->flags |= PF_THREAD_BOUND;
+                wake_up_process(rescuer->task);
         }
 
         /*
@@ -2065,16 +2653,12 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
 
         spin_unlock(&workqueue_lock);
 
-        cpu_maps_update_done();
-
-        if (failed) {
-                destroy_workqueue(wq);
-                wq = NULL;
-        }
         return wq;
 err:
         if (wq) {
                 free_cwqs(wq->cpu_wq);
+                free_cpumask_var(wq->mayday_mask);
+                kfree(wq->rescuer);
                 kfree(wq);
         }
         return NULL;
@@ -2097,42 +2681,26 @@ void destroy_workqueue(struct workqueue_struct *wq)
          * wq list is used to freeze wq, remove from list after
          * flushing is complete in case freeze races us.
          */
-        cpu_maps_update_begin();
         spin_lock(&workqueue_lock);
         list_del(&wq->list);
         spin_unlock(&workqueue_lock);
-        cpu_maps_update_done();
 
+        /* sanity check */
         for_each_possible_cpu(cpu) {
                 struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
-                struct global_cwq *gcwq = cwq->gcwq;
                 int i;
 
-                if (cwq->worker) {
-                retry:
-                        spin_lock_irq(&gcwq->lock);
-                        /*
-                         * Worker can only be destroyed while idle.
-                         * Wait till it becomes idle.  This is ugly
-                         * and prone to starvation.  It will go away
-                         * once dynamic worker pool is implemented.
-                         */
-                        if (!(cwq->worker->flags & WORKER_IDLE)) {
-                                spin_unlock_irq(&gcwq->lock);
-                                msleep(100);
-                                goto retry;
-                        }
-                        destroy_worker(cwq->worker);
-                        cwq->worker = NULL;
-                        spin_unlock_irq(&gcwq->lock);
-                }
-
                 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_cpumask_var(wq->mayday_mask);
+        }
+
         free_cwqs(wq->cpu_wq);
         kfree(wq);
 }
@@ -2141,10 +2709,18 @@ EXPORT_SYMBOL_GPL(destroy_workqueue);
 /*
  * CPU hotplug.
  *
- * CPU hotplug is implemented by allowing cwqs to be detached from
- * CPU, running with unbound workers and allowing them to be
- * reattached later if the cpu comes back online.  A separate thread
- * is created to govern cwqs in such state and is called the trustee.
+ * 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.
  *
@@ -2152,11 +2728,12 @@ EXPORT_SYMBOL_GPL(destroy_workqueue);
  *              new trustee is started with this state.
  *
  * IN_CHARGE    Once started, trustee will enter this state after
- *              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.
+ *              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
@@ -2167,7 +2744,9 @@ EXPORT_SYMBOL_GPL(destroy_workqueue);
  * 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 transits to DONE.
+ *              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.
@@ -2233,17 +2812,24 @@ 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);
         /*
-         * Make all workers rogue.  Trustee must be bound to the
-         * target cpu and can't be cancelled.
+         * 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_set_flags(worker, WORKER_ROGUE, false);
@@ -2252,6 +2838,28 @@ static int __cpuinit trustee_thread(void *__gcwq)
                 worker_set_flags(worker, WORKER_ROGUE, false);
 
         /*
+         * 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.  gcwq->nr_running should
+         * be zero and will stay that way, making need_more_worker()
+         * and keep_working() always return true as long as the
+         * worklist is not empty.
+         */
+        WARN_ON_ONCE(atomic_read(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
@@ -2263,18 +2871,90 @@ static int __cpuinit trustee_thread(void *__gcwq)
         /*
          * 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.
-         * Note that if the gcwq is frozen, there may be frozen works
-         * in freezeable cwqs.  Don't declare completion while frozen.
+         * 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_set_flags(worker, WORKER_ROGUE, false);
+                                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_set_flags(worker, WORKER_REBIND, false);
+                worker_clr_flags(worker, 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, keventd_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;
@@ -2313,10 +2993,8 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
         unsigned int cpu = (unsigned long)hcpu;
         struct global_cwq *gcwq = get_gcwq(cpu);
         struct task_struct *new_trustee = NULL;
-        struct worker *worker;
-        struct hlist_node *pos;
+        struct worker *uninitialized_var(new_worker);
         unsigned long flags;
-        int i;
 
         action &= ~CPU_TASKS_FROZEN;
 
@@ -2327,6 +3005,15 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
                 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 */
@@ -2340,26 +3027,50 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
                 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);
                 }
 
-                /* clear ROGUE from all workers */
-                list_for_each_entry(worker, &gcwq->idle_list, entry)
-                        worker_clr_flags(worker, WORKER_ROGUE);
-
-                for_each_busy_worker(worker, i, pos, gcwq)
-                        worker_clr_flags(worker, WORKER_ROGUE);
+                /*
+                 * 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;
         }
 
@@ -2548,10 +3259,10 @@ void thaw_workqueues(void)
                         if (wq->single_cpu == gcwq->cpu &&
                             !cwq->nr_active && list_empty(&cwq->delayed_works))
                                 cwq_unbind_single_cpu(cwq);
-
-                        wake_up_process(cwq->worker->task);
                 }
 
+                wake_up_worker(gcwq);
+
                 spin_unlock_irq(&gcwq->lock);
         }
 
@@ -2588,12 +3299,31 @@ void __init init_workqueues(void)
                 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_cpu(cpu) {
+                struct global_cwq *gcwq = get_gcwq(cpu);
+                struct worker *worker;
+
+                worker = create_worker(gcwq, true);
+                BUG_ON(!worker);
+                spin_lock_irq(&gcwq->lock);
+                start_worker(worker);
+                spin_unlock_irq(&gcwq->lock);
+        }
+
         keventd_wq = create_workqueue("events");
         BUG_ON(!keventd_wq);
 }