[PATCH] blk-mq: streamline handling of q->mq_ops->queue_rq result

[Ming Lei <ming.lei@redhat.com>]

Current handling of q->mq_ops->queue_rq result is a bit ugly:

- two branches which needs to 'continue' have to check if the
dispatch local list is empty, otherwise one bad request may
be retrieved via 'rq = list_first_entry(list, struct request, queuelist);'

- the branch of 'if (unlikely(ret != BLK_STS_OK))' isn't easy
to follow, since it is actually one error branch.

Streamline this handling, so the code becomes more readable, meantime
potential kernel oops can be avoided in case that the last request in
local dispatch list is failed.

Fixes: fc17b6534eb8 ("blk-mq: switch ->queue_rq return value to blk_status_t")
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 65e0846fd065..c3862144a2a7 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1407,7 +1407,10 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 		if (nr_budgets)
 			nr_budgets--;
 		ret = q->mq_ops->queue_rq(hctx, &bd);
-		if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE) {
+		if (likely(ret == BLK_STS_OK)) {
+			queued++;
+		} else if (ret == BLK_STS_RESOURCE ||
+				ret == BLK_STS_DEV_RESOURCE) {
 			blk_mq_handle_dev_resource(rq, list);
 			break;
 		} else if (ret == BLK_STS_ZONE_RESOURCE) {
@@ -1417,18 +1420,10 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 			 * accept.
 			 */
 			blk_mq_handle_zone_resource(rq, &zone_list);
-			if (list_empty(list))
-				break;
-			continue;
-		}
-
-		if (unlikely(ret != BLK_STS_OK)) {
+		} else {
 			errors++;
 			blk_mq_end_request(rq, BLK_STS_IOERR);
-			continue;
 		}
-
-		queued++;
 	} while (!list_empty(list));
 
 	if (!list_empty(&zone_list))
-- 
2.25.2