[PATCH 4.4 22/67] MD: make bio mergeable

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Shaohua Li <shli@xxxxxx>

commit 9c573de3283af007ea11c17bde1e4568d9417328 upstream.

blk_queue_split marks bio unmergeable, which makes sense for normal bio.
But if dispatching the bio to underlayer disk, the blk_queue_split
checks are invalid, hence it's possible the bio becomes mergeable.

In the reported bug, this bug causes trim against raid0 performance slash
https://bugzilla.kernel.org/show_bug.cgi?id=117051

Reported-and-tested-by: Park Ju Hyung <qkrwngud825@xxxxxxxxx>
Fixes: 6ac45aeb6bca(block: avoid to merge splitted bio)
Cc: Ming Lei <ming.lei@xxxxxxxxxxxxx>
Cc: Neil Brown <neilb@xxxxxxx>
Reviewed-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Shaohua Li <shli@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/md/md.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -293,6 +293,8 @@ static blk_qc_t md_make_request(struct r
 	 * go away inside make_request
 	 */
 	sectors = bio_sectors(bio);
+	/* bio could be mergeable after passing to underlayer */
+	bio->bi_rw &= ~REQ_NOMERGE;
 	mddev->pers->make_request(mddev, bio);
 
 	cpu = part_stat_lock();