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>

diff --git a/block/blk-core.c b/block/blk-core.c
index e0a094fddee5f3e16b660c8cab189987663cb7f7..089e890ab208fd01efbda68aea4fdb47aaab1353 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -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;