md/raid5: round discard alignment up to power of 2.

blkdev_issue_discard currently assumes that the granularity
is a power of 2.  So in raid5, round the chosen number up to
avoid embarrassment.

Cc: Shaohua Li <shli@kernel.org>
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index c5439dce0295..baea94f0670a 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5529,6 +5529,10 @@ static int run(struct mddev *mddev)
                  * discard data disk but write parity disk
                  */
                 stripe = stripe * PAGE_SIZE;
+                /* Round up to power of 2, as discard handling
+                 * currently assumes that */
+                while ((stripe-1) & stripe)
+                        stripe = (stripe | (stripe-1)) + 1;
                 mddev->queue->limits.discard_alignment = stripe;
                 mddev->queue->limits.discard_granularity = stripe;
                 /*