1 files changed, 36 insertions, 1 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 383548ed0b54..1e1373bcb3e3 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1825,10 +1825,45 @@ 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;
 
         /*