[dm-devel] [PATCH] dm thin metadata: fix lockdep complaint

[Theodore Ts'o]

[ 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.

Signed-off-by: Theodore Ts'o <tytso at mit.edu>
---
 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 fc9947d6210c..76b6b323bf4b 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;
-- 
2.24.1