On Wed, Mar 16, 2022 at 10:22:37PM +0900, Naohiro Aota wrote:
> When btrfs balance is interrupted with umount, the background balance
> resumes on the next mount. There is a potential deadlock with FS freezing
> here like as described in commit 26559780b953 ("btrfs: zoned: mark
> relocation as writing").
>
> Mark the process as sb_writing. To preserve the order of sb_start_write()
> (or mnt_want_write_file()) and btrfs_exclop_start(), call sb_start_write()
> at btrfs_resume_balance_async() before taking fs_info->super_lock.
This paragraph is now outdated, it should go away as it applied only to v1.
The ordering problem is no longer relevant and we don't do anything at
btrfs_resume_balance_async() anymore.
>
> Cc: stable@xxxxxxxxxxxxxxx # 4.9+
> Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
Other than that, it looks good.
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Thanks.
> ---
> fs/btrfs/volumes.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 3fd17e87815a..3471698fd831 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -4430,10 +4430,12 @@ static int balance_kthread(void *data)
> struct btrfs_fs_info *fs_info = data;
> int ret = 0;
>
> + sb_start_write(fs_info->sb);
> mutex_lock(&fs_info->balance_mutex);
> if (fs_info->balance_ctl)
> ret = btrfs_balance(fs_info, fs_info->balance_ctl, NULL);
> mutex_unlock(&fs_info->balance_mutex);
> + sb_end_write(fs_info->sb);
>
> return ret;
> }
> --
> 2.35.1
>
