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    Subject[PATCH 5.5 005/189] 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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