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Subject[PATCH 5.4 007/168] dm thin metadata: fix lockdep complaint
Date
From: Theodore Ts'o <tytso@mit.edu>

[ Upstream commit 3918e0667bbac99400b44fa5aef3f8be2eeada4a ]

[ 3934.173244] ======================================================
[ 3934.179572] WARNING: possible circular locking dependency detected
[ 3934.185884] 5.4.21-xfstests #1 Not tainted
[ 3934.190151] ------------------------------------------------------
[ 3934.196673] dmsetup/8897 is trying to acquire lock:
[ 3934.201688] ffffffffbce82b18 (shrinker_rwsem){++++}, at: unregister_shrinker+0x22/0x80
[ 3934.210268]
but task is already holding lock:
[ 3934.216489] ffff92a10cc5e1d0 (&pmd->root_lock){++++}, at: dm_pool_metadata_close+0xba/0x120
[ 3934.225083]
which lock already depends on the new lock.

[ 3934.564165] Chain exists of:
shrinker_rwsem --> &journal->j_checkpoint_mutex --> &pmd->root_lock

For a more detailed lockdep report, please see:

https://lore.kernel.org/r/20200220234519.GA620489@mit.edu

We shouldn't need to hold the lock while are just tearing down and
freeing the whole metadata pool structure.

Fixes: 44d8ebf436399a4 ("dm thin metadata: use pool locking at end of dm_pool_metadata_close")
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/md/dm-thin-metadata.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c
index 8bb723f1a569a..4cd8868f80040 100644
--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -960,9 +960,9 @@ int dm_pool_metadata_close(struct dm_pool_metadata *pmd)
DMWARN("%s: __commit_transaction() failed, error = %d",
__func__, r);
}
+ pmd_write_unlock(pmd);
if (!pmd->fail_io)
__destroy_persistent_data_objects(pmd);
- pmd_write_unlock(pmd);

kfree(pmd);
return 0;
--
2.20.1


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