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    Subject[PATCH 4.4 91/91] Btrfs: use down_read_nested to make lockdep silent
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Liu Bo <bo.li.liu@oracle.com>


    [ Upstream commit e321f8a801d7b4c40da8005257b05b9c2b51b072 ]

    If @block_group is not @used_bg, it'll try to get @used_bg's lock without
    droping @block_group 's lock and lockdep has throwed a scary deadlock warning
    about it.
    Fix it by using down_read_nested.

    Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
    Reviewed-by: David Sterba <dsterba@suse.com>
    Signed-off-by: David Sterba <dsterba@suse.com>
    Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    fs/btrfs/extent-tree.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
    index e46e7fbe1b34..14a37ff0b9e3 100644
    --- a/fs/btrfs/extent-tree.c
    +++ b/fs/btrfs/extent-tree.c
    @@ -7401,7 +7401,8 @@ btrfs_lock_cluster(struct btrfs_block_group_cache *block_group,

    spin_unlock(&cluster->refill_lock);

    - down_read(&used_bg->data_rwsem);
    + /* We should only have one-level nested. */
    + down_read_nested(&used_bg->data_rwsem, SINGLE_DEPTH_NESTING);

    spin_lock(&cluster->refill_lock);
    if (used_bg == cluster->block_group)
    --
    2.13.4


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