Btrfs: fix possible deadlock when opening a seed device

The correct lock order is uuid_mutex -> volume_mutex -> chunk_mutex,
but when we mount a filesystem which has backing seed devices, we have
this lock chain:

    open_ctree()
        lock(chunk_mutex);
        read_chunk_tree();
            read_one_dev();
                open_seed_devices();
                    lock(uuid_mutex);

and then we hit a lockdep splat.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

1 files changed, 0 insertions, 2 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3f9d5551e582..858ab347413e 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2270,9 +2270,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
            (unsigned long)btrfs_header_chunk_tree_uuid(chunk_root->node),
            BTRFS_UUID_SIZE);
 
-        mutex_lock(&fs_info->chunk_mutex);
         ret = btrfs_read_chunk_tree(chunk_root);
-        mutex_unlock(&fs_info->chunk_mutex);
         if (ret) {
                 printk(KERN_WARNING "btrfs: failed to read chunk tree on %s\n",
                        sb->s_id);