[PATCH] md/raid5: complete discard bios while reshape is active

[Genjian]

From: Genjian Zhang <zhanggenjian@xxxxxxxxxx>

make_discard_request() returns without completing the bio when reshape
is in progress. Discard callers block in submit_bio_wait()
waiting for a completion that never arrives.  The caller hangs in
uninterruptible sleep, and this does not resolve when reshape finishes.

Complete the bio with BLK_STS_AGAIN so userspace can retry after reshape,
consistent with the existing policy of not processing discard during
reshape.

Tested on a loop-backed RAID5 array during mdadm --grow: without this
patch, blkdiscard hangs in bio_await() and remains in uninterruptible
sleep after md reports "reshape done"; with this patch it returns
-EAGAIN instead.

Signed-off-by: Genjian Zhang <zhanggenjian@xxxxxxxxxx>
---
 drivers/md/raid5.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index ffb5fcde54a9..4c3b42b2af85 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5722,9 +5722,11 @@ static void make_discard_request(struct mddev *mddev, struct bio *bi)
 	if (WARN_ON_ONCE(bi->bi_opf & REQ_NOWAIT))
 		return;
 
-	if (mddev->reshape_position != MaxSector)
+	if (mddev->reshape_position != MaxSector) {
 		/* Skip discard while reshape is happening */
+		bio_endio_status(bi, BLK_STS_AGAIN);
 		return;
+	}
 
 	if (!raid5_discard_limits(mddev, bi))
 		return;
-- 
2.43.0