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

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Date:   Sat, 11 Jan 2020 10:50:22 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Roman Penyaev <rpenyaev@...e.de>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 103/165] block: end bio with BLK_STS_AGAIN in case of non-mq devs and REQ_NOWAIT

From: Roman Penyaev <rpenyaev@...e.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@...e.de>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.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