From: Ming Lei <ming.lei@redhat.com>
Date: Wed, 1 Jul 2020 21:58:57 +0800
Subject: [PATCH] blk-mq: streamline handling of q->mq_ops->queue_rq result
References: bsc#1175995,jsc#SLE-15608
Git-commit: 7bf137298cb73afdb8c5536e474f7ba71ab1c235
Patch-mainline: v5.9-rc1

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")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Hannes Reinecke <hare@suse.de>
---
 block/blk-mq.c | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 4488cf409f80..2abd296ca72c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1381,30 +1381,28 @@ 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) {
-			blk_mq_handle_dev_resource(rq, list);
+		switch (ret) {
+		case BLK_STS_OK:
+			queued++;
 			break;
-		} else if (ret == BLK_STS_ZONE_RESOURCE) {
+		case BLK_STS_RESOURCE:
+		case BLK_STS_DEV_RESOURCE:
+			blk_mq_handle_dev_resource(rq, list);
+			goto out;
+		case BLK_STS_ZONE_RESOURCE:
 			/*
 			 * Move the request to zone_list and keep going through
 			 * the dispatch list to find more requests the drive can
 			 * accept.
 			 */
 			blk_mq_handle_zone_resource(rq, &zone_list);
-			if (list_empty(list))
-				break;
-			continue;
-		}
-
-		if (unlikely(ret != BLK_STS_OK)) {
+			break;
+		default:
 			errors++;
 			blk_mq_end_request(rq, BLK_STS_IOERR);
-			continue;
 		}
-
-		queued++;
 	} while (!list_empty(list));
-
+out:
 	if (!list_empty(&zone_list))
 		list_splice_tail_init(&zone_list, list);
 
-- 
2.16.4