[ 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: 44d8ebf4 ("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>