[PATCH 5.4 04/32] Revert "Revert "block: end bio with BLK_STS_AGAIN in case of non-mq devs and REQ_NOWAIT""

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gre...@linuxfoundation.org>

This reverts commit bba91cdba612fbce4f8575c5d94d2b146fb83ea3 which is
commit b0beb28097fa04177b3769f4bb7a0d0d9c4ae76e upstream.

It breaks things in 5.4.y, so let's drop it.

Reported-by: Andres Freund <and...@anarazel.de>
Cc: Bijan Mottahedeh <bijan.mottahe...@oracle.com>
CC: Jens Axboe <ax...@kernel.dk>
Cc: Sasha Levin <sas...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 block/blk-core.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -886,11 +886,14 @@ generic_make_request_checks(struct 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;