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>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3f9d555..858ab34 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2270,9 +2270,7 @@
(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);
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 563ef65..fbb493b 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3506,7 +3506,7 @@
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 @@
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 @@
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 @@
}
ret = 0;
error:
+ unlock_chunks(root);
+ mutex_unlock(&uuid_mutex);
+
btrfs_free_path(path);
return ret;
}