blk-mq: don't commit_rqs() if none were queued

Unburden the drivers from checking if a call to commit_rqs() is valid by
not calling it when there are no requests to commit.

Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -1289,7 +1289,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
 		 * the driver there was more coming, but that turned out to
 		 * be a lie.
 		 */
-		if (q->mq_ops->commit_rqs)
+		if (q->mq_ops->commit_rqs && queued)
 			q->mq_ops->commit_rqs(hctx);
 
 		spin_lock(&hctx->lock);
@@ -1911,6 +1911,8 @@ blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last)
 void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 		struct list_head *list)
 {
+	int queued = 0;
+
 	while (!list_empty(list)) {
 		blk_status_t ret;
 		struct request *rq = list_first_entry(list, struct request,
@@ -1926,15 +1928,16 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 				break;
 			}
 			blk_mq_end_request(rq, ret);
-		}
+		} else
+			queued++;
 	}
 
 	/*
 	 * If we didn't flush the entire list, we could have told
 	 * the driver there was more coming, but that turned out to
 	 * be a lie.
 	 */
-	if (!list_empty(list) && hctx->queue->mq_ops->commit_rqs)
+	if (!list_empty(list) && hctx->queue->mq_ops->commit_rqs && queued)
 		hctx->queue->mq_ops->commit_rqs(hctx);
 }