From 044ca491d4086dc5bf233e9fcb71db52df32f633 Mon Sep 17 00:00:00 2001
From: Ming-Hung Tsai <mtsai@redhat.com>
Date: Wed, 4 Mar 2026 19:56:28 +0800
Subject: [PATCH] dm cache metadata: fix memory leak on metadata abort retry

When failing to acquire the root_lock in dm_cache_metadata_abort because
the block_manager is read-only, the temporary block_manager created
outside the root_lock is not properly released, causing a memory leak.

Reproduce steps:

This can be reproduced by reloading a new table while the metadata
is read-only. While the second call to dm_cache_metadata_abort is
caused by lack of support for table preload in dm-cache, mentioned
in commit 9b1cc9f251af ("dm cache: share cache-metadata object across
inactive and active DM tables"), it exposes the memory leak in
dm_cache_metadata_abort when the function is called multiple times.
Specifically, dm-cache fails to sync the new cache object's mode during
preresume, creating the reproducer condition.

This issue could also occur through concurrent metadata_operation_failed
calls due to races in cache mode updates, but the table preload scenario
below provides a reliable reproducer.

1. Create a cache device with some faulty trailing metadata blocks

dmsetup create cmeta <<EOF
0 200 linear /dev/sdc 0
200 7992 error
EOF
dmsetup create cdata --table "0 131072 linear /dev/sdc 8192"
dmsetup create corig --table "0 262144 linear /dev/sdc 262144"
dd if=/dev/zero of=/dev/mapper/cmeta bs=4k count=1 oflag=direct
dmsetup create cache --table "0 131072 cache /dev/mapper/cmeta \
/dev/mapper/cdata /dev/mapper/corig 128 1 writethrough smq 0"

2. Suspend and resume the cache to start a new metadata transaction and
   trigger metadata io errors on the next metadata commit.

dmsetup suspend cache
dmsetup resume cache

3. Write to the cache device to update metadata

fio --filename=/dev/mapper/cache --name test --rw=randwrite --bs=4k \
--randrepeat=0 --direct=1 --size 64k

4. Preload the same table

dmsetup reload cache --table "$(dmsetup table cache)"

5. Resume the new table. This triggers the memory leak.

dmsetup suspend cache
dmsetup resume cache

kmemleak logs:

<snip>
unreferenced object 0xffff8880080c2010 (size 16):
  comm "dmsetup", pid 132, jiffies 4294982580
  hex dump (first 16 bytes):
    00 38 b9 07 80 88 ff ff 6a 6b 6b 6b 6b 6b 6b a5 ...
  backtrace (crc 3118f31c):
    kmemleak_alloc+0x28/0x40
    __kmalloc_cache_noprof+0x3d9/0x510
    dm_block_manager_create+0x51/0x140
    dm_cache_metadata_abort+0x85/0x320
    metadata_operation_failed+0x103/0x1e0
    cache_preresume+0xacd/0xe70
    dm_table_resume_targets+0xd3/0x320
    __dm_resume+0x1b/0xf0
    dm_resume+0x127/0x170
<snip>

Fixes: 352b837a5541 ("dm cache: Fix ABBA deadlock between shrink_slab and dm_cache_metadata_abort")
Signed-off-by: Ming-Hung Tsai <mtsai@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
---
 drivers/md/dm-cache-metadata.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/md/dm-cache-metadata.c b/drivers/md/dm-cache-metadata.c
index 25b8aebdca53..acd9b179fcb3 100644
--- a/drivers/md/dm-cache-metadata.c
+++ b/drivers/md/dm-cache-metadata.c
@@ -1023,6 +1023,12 @@ static bool cmd_write_lock(struct dm_cache_metadata *cmd)
 			return;			\
 	} while (0)
 
+#define WRITE_LOCK_OR_GOTO(cmd, label)		\
+	do {					\
+		if (!cmd_write_lock((cmd)))	\
+			goto label;		\
+	} while (0)
+
 #define WRITE_UNLOCK(cmd) \
 	up_write(&(cmd)->root_lock)
 
@@ -1780,11 +1786,8 @@ int dm_cache_metadata_abort(struct dm_cache_metadata *cmd)
 	new_bm = dm_block_manager_create(cmd->bdev, DM_CACHE_METADATA_BLOCK_SIZE << SECTOR_SHIFT,
 					 CACHE_MAX_CONCURRENT_LOCKS);
 
-	WRITE_LOCK(cmd);
-	if (cmd->fail_io) {
-		WRITE_UNLOCK(cmd);
-		goto out;
-	}
+	/* cmd_write_lock() already checks fail_io with cmd->root_lock held */
+	WRITE_LOCK_OR_GOTO(cmd, out);
 
 	__destroy_persistent_data_objects(cmd, false);
 	old_bm = cmd->bm;