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Btrfs: fix possible deadlock when opening a seed device

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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>
This commit is contained in:
Li Zefan 2011-12-07 11:38:24 +08:00
parent c7c144db53
commit b367e47fb3
2 changed files with 7 additions and 4 deletions
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2
fs/btrfs/disk-io.c
View File

@ -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);

9
fs/btrfs/volumes.c
View File

@ -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 @@ again:
}
ret = 0;
error:
unlock_chunks(root);
mutex_unlock(&uuid_mutex);
btrfs_free_path(path);
return ret;
}