blk-mq: fix sbitmap ws_active for shared tags

We now wrap sbitmap waitqueues in an active counter, so we can avoid iterating wakeups unless we have waiters there. This works as long as everyone that's manipulating the waitqueues use the proper helpers. For the tag wait case for shared tags, however, we add ourselves to the waitqueue without incrementing/decrementing the ->ws_active count. This means that wakeups can take a long time to happen. Fix this by manually doing the inc/dec as needed for the wait queue handling. Reported-by: Michael Leun <[email protected]> Tested-by: Michael Leun <[email protected]> Cc: [email protected] Reviewed-by: Omar Sandoval <[email protected]> Fixes: 5d2ee71 ("sbitmap: optimize wakeup check") Signed-off-by: Jens Axboe <[email protected]>
chewitt · Mar 25, 2019 · e861857 · e861857
1 parent 9e75ad5
commit e861857
Showing 1 changed file with 11 additions and 2 deletions.
diff --git a/block/blk-mq.c b/block/blk-mq.c
@@ -1072,7 +1072,13 @@ static int blk_mq_dispatch_wake(wait_queue_entry_t *wait, unsigned mode,
 	hctx = container_of(wait, struct blk_mq_hw_ctx, dispatch_wait);
 
 	spin_lock(&hctx->dispatch_wait_lock);
-	list_del_init(&wait->entry);
+	if (!list_empty(&wait->entry)) {
+		struct sbitmap_queue *sbq;
+
+		list_del_init(&wait->entry);
+		sbq = &hctx->tags->bitmap_tags;
+		atomic_dec(&sbq->ws_active);
+	}
 	spin_unlock(&hctx->dispatch_wait_lock);
 
 	blk_mq_run_hw_queue(hctx, true);
@@ -1088,6 +1094,7 @@ static int blk_mq_dispatch_wake(wait_queue_entry_t *wait, unsigned mode,
 static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx *hctx,
 				 struct request *rq)
 {
+	struct sbitmap_queue *sbq = &hctx->tags->bitmap_tags;
 	struct wait_queue_head *wq;
 	wait_queue_entry_t *wait;
 	bool ret;
@@ -1110,7 +1117,7 @@ static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx *hctx,
 	if (!list_empty_careful(&wait->entry))
 		return false;
 
-	wq = &bt_wait_ptr(&hctx->tags->bitmap_tags, hctx)->wait;
+	wq = &bt_wait_ptr(sbq, hctx)->wait;
 
 	spin_lock_irq(&wq->lock);
 	spin_lock(&hctx->dispatch_wait_lock);
@@ -1120,6 +1127,7 @@ static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx *hctx,
 		return false;
 	}
 
+	atomic_inc(&sbq->ws_active);
 	wait->flags &= ~WQ_FLAG_EXCLUSIVE;
 	__add_wait_queue(wq, wait);
 
@@ -1140,6 +1148,7 @@ static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx *hctx,
 	 * someone else gets the wakeup.
 	 */
 	list_del_init(&wait->entry);
+	atomic_dec(&sbq->ws_active);
 	spin_unlock(&hctx->dispatch_wait_lock);
 	spin_unlock_irq(&wq->lock);