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block: end bio with BLK_STS_AGAIN in case of non-mq devs and REQ_NOWAIT 

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>
alistair/sunxi64-5.5-dsi
Roman Penyaev 2019-12-17 16:54:07 +01:00 committed by Jens Axboe
parent 1c05839aa9
commit c58c1f8343
1 changed files with 7 additions and 4 deletions
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11
block/blk-core.c
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@ -885,11 +885,14 @@ 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;