1 files changed, 15 insertions, 22 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 64d0edf428f8..a2dccfe1acec 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -68,6 +68,7 @@ enum {
          * attach_mutex to avoid changing binding state while
          * worker_attach_to_pool() is in progress.
          */
+        POOL_MANAGER_ACTIVE     = 1 << 0,       /* being managed */
         POOL_DISASSOCIATED      = 1 << 2,       /* cpu can't serve workers */
 
         /* worker flags */
@@ -165,7 +166,6 @@ struct worker_pool {
                                                 /* L: hash of busy workers */
 
         /* see manage_workers() for details on the two manager mutexes */
-        struct mutex            manager_arb;    /* manager arbitration */
         struct worker           *manager;       /* L: purely informational */
         struct mutex            attach_mutex;   /* attach/detach exclusion */
         struct list_head        workers;        /* A: attached workers */
@@ -299,6 +299,7 @@ static struct workqueue_attrs *wq_update_unbound_numa_attrs_buf;
 
 static DEFINE_MUTEX(wq_pool_mutex);     /* protects pools and workqueues list */
 static DEFINE_SPINLOCK(wq_mayday_lock); /* protects wq->maydays list */
+static DECLARE_WAIT_QUEUE_HEAD(wq_manager_wait); /* wait for manager to go away */
 
 static LIST_HEAD(workqueues);           /* PR: list of all workqueues */
 static bool workqueue_freezing;         /* PL: have wqs started freezing? */
@@ -801,7 +802,7 @@ static bool need_to_create_worker(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_arb);
+        bool managing = pool->flags & POOL_MANAGER_ACTIVE;
         int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
         int nr_busy = pool->nr_workers - nr_idle;
 
@@ -1980,24 +1981,17 @@ static bool manage_workers(struct worker *worker)
 {
         struct worker_pool *pool = worker->pool;
 
-        /*
-         * Anyone who successfully grabs manager_arb wins the arbitration
-         * and becomes the manager.  mutex_trylock() on pool->manager_arb
-         * failure while holding pool->lock reliably indicates that someone
-         * else is managing the pool and the worker which failed trylock
-         * can proceed to executing work items.  This means that anyone
-         * grabbing manager_arb is responsible for actually performing
-         * manager duties.  If manager_arb is grabbed and released without
-         * actual management, the pool may stall indefinitely.
-         */
-        if (!mutex_trylock(&pool->manager_arb))
+        if (pool->flags & POOL_MANAGER_ACTIVE)
                 return false;
+
+        pool->flags |= POOL_MANAGER_ACTIVE;
         pool->manager = worker;
 
         maybe_create_worker(pool);
 
         pool->manager = NULL;
-        mutex_unlock(&pool->manager_arb);
+        pool->flags &= ~POOL_MANAGER_ACTIVE;
+        wake_up(&wq_manager_wait);
         return true;
 }
 
@@ -3248,7 +3242,6 @@ static int init_worker_pool(struct worker_pool *pool)
         setup_timer(&pool->mayday_timer, pool_mayday_timeout,
                     (unsigned long)pool);
 
-        mutex_init(&pool->manager_arb);
         mutex_init(&pool->attach_mutex);
         INIT_LIST_HEAD(&pool->workers);
 
@@ -3318,13 +3311,15 @@ static void put_unbound_pool(struct worker_pool *pool)
         hash_del(&pool->hash_node);
 
         /*
-         * Become the manager and destroy all workers.  Grabbing
-         * manager_arb prevents @pool's workers from blocking on
-         * attach_mutex.
+         * Become the manager and destroy all workers.  This prevents
+         * @pool's workers from blocking on attach_mutex.  We're the last
+         * manager and @pool gets freed with the flag set.
          */
-        mutex_lock(&pool->manager_arb);
-
         spin_lock_irq(&pool->lock);
+        wait_event_lock_irq(wq_manager_wait,
+                            !(pool->flags & POOL_MANAGER_ACTIVE), pool->lock);
+        pool->flags |= POOL_MANAGER_ACTIVE;
+
         while ((worker = first_idle_worker(pool)))
                 destroy_worker(worker);
         WARN_ON(pool->nr_workers || pool->nr_idle);
@@ -3338,8 +3333,6 @@ static void put_unbound_pool(struct worker_pool *pool)
         if (pool->detach_completion)
                 wait_for_completion(pool->detach_completion);
 
-        mutex_unlock(&pool->manager_arb);
-
         /* shut down the timers */
         del_timer_sync(&pool->idle_timer);
         del_timer_sync(&pool->mayday_timer);