[PATCH 5.4 103/165] block: end bio with BLK_STS_AGAIN in case of non-mq devs and REQ_NOWAIT

Greg Kroah-Hartman
2020-01-11T10:28:08Z

From: Roman Penyaev <rpenyaev@suse.de>

[ Upstream commit c58c1f83436b501d45d4050fd1296d71a9760bcb ]

Non-mq devs do not honor REQ_NOWAIT so give a chance to the caller to repeat
request gracefully on -EAGAIN error.

The problem is well reproduced using io_uring:

mkfs.ext4 /dev/ram0
mount /dev/ram0 /mnt

# Preallocate a file
dd if=/dev/zero of=/mnt/file bs=1M count=1

# Start fio with io_uring and get -EIO
fio --rw=write --ioengine=io_uring --size=1M --direct=1 --name=job --filename=/mnt/file

Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/blk-core.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index d5e668ec751b..1075aaff606d 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -886,11 +886,14 @@ generic_make_request_checks(struct bio *bio)
}

/*
- * For a REQ_NOWAIT based request, return -EOPNOTSUPP
- * if queue is not a request based queue.
+ * Non-mq queues do not honor REQ_NOWAIT, so complete a bio
+ * with BLK_STS_AGAIN status in order to catch -EAGAIN and
+ * to give a chance to the caller to repeat request gracefully.
*/
- if ((bio->bi_opf & REQ_NOWAIT) && !queue_is_mq(q))
- goto not_supported;
+ if ((bio->bi_opf & REQ_NOWAIT) && !queue_is_mq(q)) {
+ status = BLK_STS_AGAIN;
+ goto end_io;
+ }

if (should_fail_bio(bio))
goto end_io;
--
2.20.1