linux-kernel - [PATCH] dm-table: Set BLK_FEAT_ATOMIC

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Message-Id: <20250502143933.1320061-1-john.g.garry@oracle.com>
Date: Fri,  2 May 2025 14:39:33 +0000
From: John Garry <john.g.garry@...cle.com>
To: agk@...hat.com, snitzer@...nel.org, mpatocka@...hat.com
Cc: dm-devel@...ts.linux.dev, linux-kernel@...r.kernel.org,
        martin.petersen@...cle.com, John Garry <john.g.garry@...cle.com>
Subject: [PATCH] dm-table: Set BLK_FEAT_ATOMIC_WRITES for target queue limits

Feature flag BLK_FEAT_ATOMIC_WRITES is not being properly set for the
target queue limits, and this means that atomic writes are not being
enabled for any dm personalities.

When calling dm_set_device_limits() -> blk_stack_limits() ->
... -> blk_stack_atomic_writes_limits(), the bottom device limits
(which corresponds to intermediate target queue limits) does not have
BLK_FEAT_ATOMIC_WRITES set, and so atomic writes can never be enabled.

Typically such a flag would be inherited from the stacked device in
dm_set_device_limits() -> blk_stack_limits() via BLK_FEAT_INHERIT_MASK,
but BLK_FEAT_ATOMIC_WRITES is not inherited as it's preferred to manually
enable on a per-personality basis.

Set BLK_FEAT_ATOMIC_WRITES manually for the intermediate target queue
limits from the stacked device to get atomic writes working.

Fixes: 3194e36488e2 ("dm-table: atomic writes support")
Signed-off-by: John Garry <john.g.garry@...cle.com>

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 9e175c5e0634..b35e48fed641 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -431,6 +431,12 @@ static int dm_set_device_limits(struct dm_target *ti, struct dm_dev *dev,
 		return 0;
 	}

+	/*
+	 * BLK_FEAT_ATOMIC_WRITES is not inherited from the bottom device in
+	 * blk_stack_limits(), so do it manually.
+	 */
+	limits->features |= (q->limits.features & BLK_FEAT_ATOMIC_WRITES);
+
 	if (blk_stack_limits(limits, &q->limits,
 			get_start_sect(bdev) + start) < 0)
 		DMWARN("%s: adding target device %pg caused an alignment inconsistency: "
-- 
2.31.1