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Commit b367e47f authored by Li Zefan's avatar Li Zefan
Browse files

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: default avatarLi Zefan <lizf@cn.fujitsu.com>
parent c7c144db

fs/btrfs/disk-io.c

+0 −2
Original line number Diff line number Diff line
@@ -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);

fs/btrfs/volumes.c

+7 −2
Original line number Diff line number Diff line
@@ -3506,7 +3506,7 @@ static int open_seed_devices(struct btrfs_root *root, u8 *fsid) 
	struct btrfs_fs_devices *fs_devices;

	int ret;



	mutex_lock(&uuid_mutex);

	BUG_ON(!mutex_is_locked(&uuid_mutex));



	fs_devices = root->fs_info->fs_devices->seed;

	while (fs_devices) {
@@ -3544,7 +3544,6 @@ static int open_seed_devices(struct btrfs_root *root, u8 *fsid) 
	fs_devices->seed = root->fs_info->fs_devices->seed;

	root->fs_info->fs_devices->seed = fs_devices;

out:

	mutex_unlock(&uuid_mutex);

	return ret;

}
@@ -3687,6 +3686,9 @@ int btrfs_read_chunk_tree(struct btrfs_root *root) 
	if (!path)

		return -ENOMEM;



	mutex_lock(&uuid_mutex);

	lock_chunks(root);



	/* first we search for all of the device items, and then we

	 * read in all of the chunk items.  This way we can create chunk

	 * mappings that reference all of the devices that are afound
@@ -3737,6 +3739,9 @@ int btrfs_read_chunk_tree(struct btrfs_root *root) 
	}

	ret = 0;

error:

	unlock_chunks(root);

	mutex_unlock(&uuid_mutex);



	btrfs_free_path(path);

	return ret;

}