Re: [PATCH 4/7] btrfs: lift uuid_mutex to callers of btrfs_open_devices

[Anand Jain <anand.jain@oracle.com>]

On 06/21/2018 01:51 AM, David Sterba wrote:
> Prepartory work to fix race between mount and device scan.
> 
> The callers will have to manage the critical section, eg.  mount wants
> to scan and then call btrfs_open_devices without the ioctl scan walking
> in and modifying the fs devices in the meantime.
> 
> Signed-off-by: David Sterba <dsterba@suse.com>

Reviewed-by: Anand Jain <anand.jain@oracle.com>

Thanks, Anand

> ---
>   fs/btrfs/super.c   | 2 ++
>   fs/btrfs/volumes.c | 4 ++--
>   2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 735402ed3154..ee82d02f5453 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -1569,7 +1569,9 @@ static struct dentry *btrfs_mount_root(struct file_system_type *fs_type,
>   		goto error_fs_info;
>   	}
>   
> +	mutex_lock(&uuid_mutex);
>   	error = btrfs_open_devices(fs_devices, mode, fs_type);
> +	mutex_unlock(&uuid_mutex);
>   	if (error)
>   		goto error_fs_info;
>   
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 958bfe1a725c..5336d9832ba4 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -1145,7 +1145,8 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
>   {
>   	int ret;
>   
> -	mutex_lock(&uuid_mutex);
> +	lockdep_assert_held(&uuid_mutex);
> +
>   	mutex_lock(&fs_devices->device_list_mutex);
>   	if (fs_devices->opened) {
>   		fs_devices->opened++;
> @@ -1155,7 +1156,6 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
>   		ret = open_fs_devices(fs_devices, flags, holder);
>   	}
>   	mutex_unlock(&fs_devices->device_list_mutex);
> -	mutex_unlock(&uuid_mutex);
>   
>   	return ret;
>   }
>