From d3afe03932758e40b6548480fc5cd04d0811e620 Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Tue, 21 Oct 2014 20:29:26 -0400 Subject: [PATCH] workqueue: use RCU to protect waitqueue stack dequeue against ABA Signed-off-by: Mathieu Desnoyers --- urcu/workqueue-fifo.h | 32 ++++++++++++++++++++++++-------- 1 file changed, 24 insertions(+), 8 deletions(-) diff --git a/urcu/workqueue-fifo.h b/urcu/workqueue-fifo.h index bc19967..0769acc 100644 --- a/urcu/workqueue-fifo.h +++ b/urcu/workqueue-fifo.h @@ -100,8 +100,11 @@ void urcu_queue_work(struct urcu_workqueue *queue, struct urcu_work *work) * worker threads when threads are busy enough to still be * running when work is enqueued. */ - if (was_empty) + if (was_empty) { + rcu_read_lock(); /* Protect stack dequeue */ (void) urcu_dequeue_wake_single(&queue->waitqueue); + rcu_read_unlock(); /* Protect stack dequeue */ + } } static inline @@ -109,7 +112,10 @@ void urcu_workqueue_wakeup_all(struct urcu_workqueue *queue) { struct urcu_waiters waiters; + rcu_read_lock(); /* Protect stack dequeue */ urcu_move_waiters(&waiters, &queue->waitqueue); + rcu_read_unlock(); /* Protect stack dequeue */ + (void) urcu_wake_all_waiters(&waiters); } @@ -142,14 +148,17 @@ void urcu_worker_unregister(struct urcu_workqueue *queue, pthread_mutex_lock(&queue->sibling_lock); cds_list_del_rcu(&worker->sibling_node); pthread_mutex_unlock(&queue->sibling_lock); - - /* - * Wait for grace period before freeing or reusing - * "worker" because used by RCU linked list. - */ - synchronize_rcu(); } + /* + * Wait for grace period before freeing or reusing + * "worker" because used by RCU linked list. + * Also prevents ABA for waitqueue stack dequeue: matches RCU + * read-side critical sections around dequeue and move all + * operations on waitqueue). + */ + synchronize_rcu(); + /* * Put any local work we still have back into the workqueue. */ @@ -163,7 +172,9 @@ void urcu_worker_unregister(struct urcu_workqueue *queue, * Wakeup worker thread if we have put work back into * workqueue that was previously empty. */ + rcu_read_lock(); /* Protect stack dequeue */ (void) urcu_dequeue_wake_single(&queue->waitqueue); + rcu_read_unlock(); /* Protect stack dequeue */ } } @@ -305,6 +316,8 @@ void urcu_accept_work(struct urcu_workqueue *queue, * the queue. */ cds_wfs_node_init(&worker->wait_node.node); + /* Protect stack dequeue against ABA */ + synchronize_rcu(); was_empty = !urcu_wait_add(&queue->waitqueue, &worker->wait_node); /* @@ -317,8 +330,11 @@ void urcu_accept_work(struct urcu_workqueue *queue, * a wake up. */ if (was_empty && !cds_wfcq_empty(&queue->head, - &queue->tail)) + &queue->tail)) { + rcu_read_lock(); /* Protect stack dequeue */ (void) urcu_dequeue_wake_single(&queue->waitqueue); + rcu_read_unlock(); /* Protect stack dequeue */ + } } else { /* * Non-NULL next pointer. We are therefore in -- 2.34.1