diff options
| -rw-r--r-- | kernel/workqueue.c | 62 |
1 files changed, 38 insertions, 24 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index f37421f..bc25bdf 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -60,8 +60,8 @@ enum { * %WORKER_UNBOUND set and concurrency management disabled, and may * be executing on any CPU. The pool behaves as an unbound one. * - * Note that DISASSOCIATED can be flipped only while holding - * assoc_mutex to avoid changing binding state while + * Note that DISASSOCIATED should be flipped only while holding + * manager_mutex to avoid changing binding state while * create_worker() is in progress. */ POOL_MANAGE_WORKERS = 1 << 0, /* need to manage workers */ @@ -149,8 +149,9 @@ struct worker_pool { DECLARE_HASHTABLE(busy_hash, BUSY_WORKER_HASH_ORDER); /* L: hash of busy workers */ + /* see manage_workers() for details on the two manager mutexes */ struct mutex manager_arb; /* manager arbitration */ - struct mutex assoc_mutex; /* protect POOL_DISASSOCIATED */ + struct mutex manager_mutex; /* manager exclusion */ struct ida worker_ida; /* L: for worker IDs */ struct workqueue_attrs *attrs; /* I: worker attributes */ @@ -1635,7 +1636,7 @@ static void rebind_workers(struct worker_pool *pool) struct worker *worker, *n; int i; - lockdep_assert_held(&pool->assoc_mutex); + lockdep_assert_held(&pool->manager_mutex); lockdep_assert_held(&pool->lock); /* dequeue and kick idle ones */ @@ -2022,31 +2023,44 @@ static bool manage_workers(struct worker *worker) struct worker_pool *pool = worker->pool; bool ret = false; + /* + * Managership is governed by two mutexes - manager_arb and + * manager_mutex. manager_arb handles arbitration of manager role. + * 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. + * + * manager_mutex is used for exclusion of actual management + * operations. The holder of manager_mutex can be sure that none + * of management operations, including creation and destruction of + * workers, won't take place until the mutex is released. Because + * manager_mutex doesn't interfere with manager role arbitration, + * it is guaranteed that the pool's management, while may be + * delayed, won't be disturbed by someone else grabbing + * manager_mutex. + */ if (!mutex_trylock(&pool->manager_arb)) return ret; /* - * To simplify both worker management and CPU hotplug, hold off - * management while hotplug is in progress. CPU hotplug path can't - * grab @pool->manager_arb 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->assoc_mutex to synchronize manager - * against CPU hotplug. - * - * assoc_mutex would always be free unless CPU hotplug is in - * progress. trylock first without dropping @pool->lock. + * With manager arbitration won, manager_mutex would be free in + * most cases. trylock first without dropping @pool->lock. */ - if (unlikely(!mutex_trylock(&pool->assoc_mutex))) { + if (unlikely(!mutex_trylock(&pool->manager_mutex))) { spin_unlock_irq(&pool->lock); - mutex_lock(&pool->assoc_mutex); + mutex_lock(&pool->manager_mutex); /* * CPU hotplug could have happened while we were waiting * for assoc_mutex. Hotplug itself can't handle us * because manager isn't either on idle or busy list, and * @pool's state and ours could have deviated. * - * As hotplug is now excluded via assoc_mutex, we can + * As hotplug is now excluded via manager_mutex, we can * simply try to bind. It will succeed or fail depending * on @pool's current state. Try it and adjust * %WORKER_UNBOUND accordingly. @@ -2068,7 +2082,7 @@ static bool manage_workers(struct worker *worker) ret |= maybe_destroy_workers(pool); ret |= maybe_create_worker(pool); - mutex_unlock(&pool->assoc_mutex); + mutex_unlock(&pool->manager_mutex); mutex_unlock(&pool->manager_arb); return ret; } @@ -3436,7 +3450,7 @@ static int init_worker_pool(struct worker_pool *pool) (unsigned long)pool); mutex_init(&pool->manager_arb); - mutex_init(&pool->assoc_mutex); + mutex_init(&pool->manager_mutex); ida_init(&pool->worker_ida); INIT_HLIST_NODE(&pool->hash_node); @@ -4076,11 +4090,11 @@ static void wq_unbind_fn(struct work_struct *work) for_each_cpu_worker_pool(pool, cpu) { WARN_ON_ONCE(cpu != smp_processor_id()); - mutex_lock(&pool->assoc_mutex); + mutex_lock(&pool->manager_mutex); spin_lock_irq(&pool->lock); /* - * We've claimed all manager positions. Make all workers + * We've blocked all manager operations. Make all workers * unbound and set DISASSOCIATED. Before this, all workers * except for the ones which are still executing works from * before the last CPU down must be on the cpu. After @@ -4095,7 +4109,7 @@ static void wq_unbind_fn(struct work_struct *work) pool->flags |= POOL_DISASSOCIATED; spin_unlock_irq(&pool->lock); - mutex_unlock(&pool->assoc_mutex); + mutex_unlock(&pool->manager_mutex); } /* @@ -4152,14 +4166,14 @@ static int __cpuinit workqueue_cpu_up_callback(struct notifier_block *nfb, case CPU_DOWN_FAILED: case CPU_ONLINE: for_each_cpu_worker_pool(pool, cpu) { - mutex_lock(&pool->assoc_mutex); + mutex_lock(&pool->manager_mutex); spin_lock_irq(&pool->lock); pool->flags &= ~POOL_DISASSOCIATED; rebind_workers(pool); spin_unlock_irq(&pool->lock); - mutex_unlock(&pool->assoc_mutex); + mutex_unlock(&pool->manager_mutex); } break; } |