1 files changed, 107 insertions, 40 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 692d97628a10..3c5a79e2134c 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -66,6 +66,7 @@ enum {
 
         /* pool flags */
         POOL_MANAGE_WORKERS     = 1 << 0,       /* need to manage workers */
+        POOL_MANAGING_WORKERS   = 1 << 1,       /* managing workers */
 
         /* worker flags */
         WORKER_STARTED          = 1 << 0,       /* started */
@@ -652,7 +653,7 @@ static bool need_to_manage_workers(struct worker_pool *pool)
 /* Do we have too many workers and should some go away? */
 static bool too_many_workers(struct worker_pool *pool)
 {
-        bool managing = mutex_is_locked(&pool->manager_mutex);
+        bool managing = pool->flags & POOL_MANAGING_WORKERS;
         int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
         int nr_busy = pool->nr_workers - nr_idle;
 
@@ -1326,6 +1327,15 @@ static void idle_worker_rebind(struct worker *worker)
 
         /* we did our part, wait for rebind_workers() to finish up */
         wait_event(gcwq->rebind_hold, !(worker->flags & WORKER_REBIND));
+
+        /*
+         * rebind_workers() shouldn't finish until all workers passed the
+         * above WORKER_REBIND wait.  Tell it when done.
+         */
+        spin_lock_irq(&worker->pool->gcwq->lock);
+        if (!--worker->idle_rebind->cnt)
+                complete(&worker->idle_rebind->done);
+        spin_unlock_irq(&worker->pool->gcwq->lock);
 }
 
 /*
@@ -1339,8 +1349,16 @@ static void busy_worker_rebind_fn(struct work_struct *work)
         struct worker *worker = container_of(work, struct worker, rebind_work);
         struct global_cwq *gcwq = worker->pool->gcwq;
 
-        if (worker_maybe_bind_and_lock(worker))
-                worker_clr_flags(worker, WORKER_REBIND);
+        worker_maybe_bind_and_lock(worker);
+
+        /*
+         * %WORKER_REBIND must be cleared even if the above binding failed;
+         * otherwise, we may confuse the next CPU_UP cycle or oops / get
+         * stuck by calling idle_worker_rebind() prematurely.  If CPU went
+         * down again inbetween, %WORKER_UNBOUND would be set, so clearing
+         * %WORKER_REBIND is always safe.
+         */
+        worker_clr_flags(worker, WORKER_REBIND);
 
         spin_unlock_irq(&gcwq->lock);
 }
@@ -1396,12 +1414,15 @@ retry:
         /* set REBIND and kick idle ones, we'll wait for these later */
         for_each_worker_pool(pool, gcwq) {
                 list_for_each_entry(worker, &pool->idle_list, entry) {
+                        unsigned long worker_flags = worker->flags;
+
                         if (worker->flags & WORKER_REBIND)
                                 continue;
 
-                        /* morph UNBOUND to REBIND */
-                        worker->flags &= ~WORKER_UNBOUND;
-                        worker->flags |= WORKER_REBIND;
+                        /* morph UNBOUND to REBIND atomically */
+                        worker_flags &= ~WORKER_UNBOUND;
+                        worker_flags |= WORKER_REBIND;
+                        ACCESS_ONCE(worker->flags) = worker_flags;
 
                         idle_rebind.cnt++;
                         worker->idle_rebind = &idle_rebind;
@@ -1419,25 +1440,15 @@ retry:
                 goto retry;
         }
 
-        /*
-         * All idle workers are rebound and waiting for %WORKER_REBIND to
-         * be cleared inside idle_worker_rebind().  Clear and release.
-         * Clearing %WORKER_REBIND from this foreign context is safe
-         * because these workers are still guaranteed to be idle.
-         */
-        for_each_worker_pool(pool, gcwq)
-                list_for_each_entry(worker, &pool->idle_list, entry)
-                        worker->flags &= ~WORKER_REBIND;
-
-        wake_up_all(&gcwq->rebind_hold);
-
-        /* rebind busy workers */
+        /* all idle workers are rebound, rebind busy workers */
         for_each_busy_worker(worker, i, pos, gcwq) {
                 struct work_struct *rebind_work = &worker->rebind_work;
+                unsigned long worker_flags = worker->flags;
 
-                /* morph UNBOUND to REBIND */
-                worker->flags &= ~WORKER_UNBOUND;
-                worker->flags |= WORKER_REBIND;
+                /* morph UNBOUND to REBIND atomically */
+                worker_flags &= ~WORKER_UNBOUND;
+                worker_flags |= WORKER_REBIND;
+                ACCESS_ONCE(worker->flags) = worker_flags;
 
                 if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
                                      work_data_bits(rebind_work)))
@@ -1449,6 +1460,34 @@ retry:
                             worker->scheduled.next,
                             work_color_to_flags(WORK_NO_COLOR));
         }
+
+        /*
+         * All idle workers are rebound and waiting for %WORKER_REBIND to
+         * be cleared inside idle_worker_rebind().  Clear and release.
+         * Clearing %WORKER_REBIND from this foreign context is safe
+         * because these workers are still guaranteed to be idle.
+         *
+         * We need to make sure all idle workers passed WORKER_REBIND wait
+         * in idle_worker_rebind() before returning; otherwise, workers can
+         * get stuck at the wait if hotplug cycle repeats.
+         */
+        idle_rebind.cnt = 1;
+        INIT_COMPLETION(idle_rebind.done);
+
+        for_each_worker_pool(pool, gcwq) {
+                list_for_each_entry(worker, &pool->idle_list, entry) {
+                        worker->flags &= ~WORKER_REBIND;
+                        idle_rebind.cnt++;
+                }
+        }
+
+        wake_up_all(&gcwq->rebind_hold);
+
+        if (--idle_rebind.cnt) {
+                spin_unlock_irq(&gcwq->lock);
+                wait_for_completion(&idle_rebind.done);
+                spin_lock_irq(&gcwq->lock);
+        }
 }
 
 static struct worker *alloc_worker(void)
@@ -1794,9 +1833,45 @@ static bool manage_workers(struct worker *worker)
         struct worker_pool *pool = worker->pool;
         bool ret = false;
 
-        if (!mutex_trylock(&pool->manager_mutex))
+        if (pool->flags & POOL_MANAGING_WORKERS)
                 return ret;
 
+        pool->flags |= POOL_MANAGING_WORKERS;
+
+        /*
+         * To simplify both worker management and CPU hotplug, hold off
+         * management while hotplug is in progress.  CPU hotplug path can't
+         * grab %POOL_MANAGING_WORKERS to achieve this because that can
+         * lead to idle worker depletion (all become busy thinking someone
+         * else is managing) which in turn can result in deadlock under
+         * extreme circumstances.  Use @pool->manager_mutex to synchronize
+         * manager against CPU hotplug.
+         *
+         * manager_mutex would always be free unless CPU hotplug is in
+         * progress.  trylock first without dropping @gcwq->lock.
+         */
+        if (unlikely(!mutex_trylock(&pool->manager_mutex))) {
+                spin_unlock_irq(&pool->gcwq->lock);
+                mutex_lock(&pool->manager_mutex);
+                /*
+                 * CPU hotplug could have happened while we were waiting
+                 * for manager_mutex.  Hotplug itself can't handle us
+                 * because manager isn't either on idle or busy list, and
+                 * @gcwq's state and ours could have deviated.
+                 *
+                 * As hotplug is now excluded via manager_mutex, we can
+                 * simply try to bind.  It will succeed or fail depending
+                 * on @gcwq's current state.  Try it and adjust
+                 * %WORKER_UNBOUND accordingly.
+                 */
+                if (worker_maybe_bind_and_lock(worker))
+                        worker->flags &= ~WORKER_UNBOUND;
+                else
+                        worker->flags |= WORKER_UNBOUND;
+
+                ret = true;
+        }
+
         pool->flags &= ~POOL_MANAGE_WORKERS;
 
         /*
@@ -1806,6 +1881,7 @@ static bool manage_workers(struct worker *worker)
         ret |= maybe_destroy_workers(pool);
         ret |= maybe_create_worker(pool);
 
+        pool->flags &= ~POOL_MANAGING_WORKERS;
         mutex_unlock(&pool->manager_mutex);
         return ret;
 }
@@ -3500,18 +3576,17 @@ static int __devinit workqueue_cpu_down_callback(struct notifier_block *nfb,
 #ifdef CONFIG_SMP
 
 struct work_for_cpu {
-        struct completion completion;
+        struct work_struct work;
         long (*fn)(void *);
         void *arg;
         long ret;
 };
 
-static int do_work_for_cpu(void *_wfc)
+static void work_for_cpu_fn(struct work_struct *work)
 {
-        struct work_for_cpu *wfc = _wfc;
+        struct work_for_cpu *wfc = container_of(work, struct work_for_cpu, work);
+
         wfc->ret = wfc->fn(wfc->arg);
-        complete(&wfc->completion);
-        return 0;
 }
 
 /**
@@ -3526,19 +3601,11 @@ static int do_work_for_cpu(void *_wfc)
  */
 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,
-        };
+        struct work_for_cpu wfc = { .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);
+        INIT_WORK_ONSTACK(&wfc.work, work_for_cpu_fn);
+        schedule_work_on(cpu, &wfc.work);
+        flush_work(&wfc.work);
         return wfc.ret;
 }
 EXPORT_SYMBOL_GPL(work_on_cpu);