[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 <gregkh@xxxxxxxxxxxxxxxxxxx>

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 <andres@xxxxxxxxxxx>
Cc: Bijan Mottahedeh <bijan.mottahedeh@xxxxxxxxxx>
CC: Jens Axboe <axboe@xxxxxxxxx>
Cc: Sasha Levin <sashal@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 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;