[SRU][F][G][PATCH 6/7] dm raid: fix discard limits for raid1 and raid10

Matthew Ruffell matthew.ruffell at canonical.com
Thu Oct 29 03:07:36 UTC 2020

From: Mike Snitzer <snitzer at redhat.com>

BugLink: https://bugs.launchpad.net/bugs/1896578

Block core warned that discard_granularity was 0 for dm-raid with
personality of raid1.  Reason is that raid_io_hints() was incorrectly
special-casing raid1 rather than raid0.

But since commit 29efc390b9462 ("md/md0: optimize raid0 discard
handling") even raid0 properly handles large discards.

Fix raid_io_hints() by removing discard limits settings for raid1.
Also, fix limits for raid10 by properly stacking underlying limits as
done in blk_stack_limits().

Depends-on: 29efc390b9462 ("md/md0: optimize raid0 discard handling")
Fixes: 61697a6abd24a ("dm: eliminate 'split_discard_bios' flag from DM target interface")
Cc: stable at vger.kernel.org
Reported-by: Zdenek Kabelac <zkabelac at redhat.com>
Reported-by: Mikulas Patocka <mpatocka at redhat.com>
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
(cherry-picked from commit e0910c8e4f87bb9f767e61a778b0d9271c4dc512)
Signed-off-by: Matthew Ruffell <matthew.ruffell at canonical.com>
 drivers/md/dm-raid.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index 10e8b2fe787b..793348ae1e8c 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -3744,12 +3744,14 @@ static void raid_io_hints(struct dm_target *ti, struct queue_limits *limits)
 	blk_limits_io_opt(limits, chunk_size_bytes * mddev_data_stripes(rs));
-	 * RAID1 and RAID10 personalities require bio splitting,
-	 * RAID0/4/5/6 don't and process large discard bios properly.
+	 * RAID10 personality requires bio splitting,
+	 * RAID0/1/4/5/6 don't and process large discard bios properly.
-	if (rs_is_raid1(rs) || rs_is_raid10(rs)) {
-		limits->discard_granularity = chunk_size_bytes;
-		limits->max_discard_sectors = rs->md.chunk_sectors;
+	if (rs_is_raid10(rs)) {
+		limits->discard_granularity = max(chunk_size_bytes,
+						  limits->discard_granularity);
+		limits->max_discard_sectors = min_not_zero(rs->md.chunk_sectors,
+							   limits->max_discard_sectors);

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