blk-mq: call commit_rqs while list empty but error happen

Blk-mq should call commit_rqs once 'bd.last != true' and no more
request will come(so virtscsi can kick the virtqueue, e.g.). We already
do that in 'blk_mq_dispatch_rq_list/blk_mq_try_issue_list_directly' while
list not empty and 'queued > 0'. However, we can seen the same scene
once the last request in list call queue_rq and return error like
BLK_STS_IOERR which will not requeue the request, and lead that list
empty but need call commit_rqs too(Or the request for virtscsi will stay
timeout until other request kick virtqueue).

We found this problem by do fsstress test with offline/online virtscsi
device repeat quickly.

Fixes: d666ba9 ("blk-mq: add mq_ops->commit_rqs()")
Reported-by: zhangyi (F) <[email protected]>
Signed-off-by: yangerkun <[email protected]>
Reviewed-by: Ming Lei <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

block/blk-mq.c

@@ -1412,6 +1412,11 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 
 	hctx->dispatched[queued_to_index(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) || errors) && q->mq_ops->commit_rqs && queued)
+		q->mq_ops->commit_rqs(hctx);
 	/*
 	 * Any items that need requeuing? Stuff them into hctx->dispatch,
 	 * that is where we will continue on next queue run.
@@ -1425,14 +1430,6 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 
 		blk_mq_release_budgets(q, nr_budgets);
 
-		/*
-		 * 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 (q->mq_ops->commit_rqs && queued)
-			q->mq_ops->commit_rqs(hctx);
-
 		spin_lock(&hctx->lock);
 		list_splice_tail_init(list, &hctx->dispatch);
 		spin_unlock(&hctx->lock);
@@ -2079,6 +2076,7 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 		struct list_head *list)
 {
 	int queued = 0;
+	int errors = 0;
 
 	while (!list_empty(list)) {
 		blk_status_t ret;
@@ -2095,6 +2093,7 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 				break;
 			}
 			blk_mq_end_request(rq, ret);
+			errors++;
 		} else
 			queued++;
 	}
@@ -2104,7 +2103,8 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 	 * the driver there was more coming, but that turned out to
 	 * be a lie.
 	 */
-	if (!list_empty(list) && hctx->queue->mq_ops->commit_rqs && queued)
+	if ((!list_empty(list) || errors) &&
+	     hctx->queue->mq_ops->commit_rqs && queued)
 		hctx->queue->mq_ops->commit_rqs(hctx);
 }