Re: [PATCH 2/4] btrfs: mark device addition as sb_writing

[Filipe Manana <fdmanana@kernel.org>]

On Fri, Mar 11, 2022 at 04:38:03PM +0900, Naohiro Aota wrote:
> btrfs_init_new_device() calls btrfs_relocate_sys_chunk() which incurs
> file-system internal writing. That writing can cause a deadlock with
> FS freezing like as described in like as described in commit
> 26559780b953 ("btrfs: zoned: mark relocation as writing").
> 
> Mark the device addition as sb_writing. This is also consistent with
> the removing device ioctl counterpart.
> 
> Fixes: 5accdf82ba25 ("fs: Improve filesystem freezing handling")

Same comment as the previous patch about this.

> Cc: stable@vger.kernel.org
> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
> ---
>  fs/btrfs/ioctl.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 238cee5b5254..ffa30fd3eed2 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -3484,6 +3484,7 @@ static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)
>  		return -EINVAL;
>  	}
>  
> +	sb_start_write(fs_info->sb);

Why not use mnt_want_write_file(), just like all the other ioctls that need
to do some change to the fs?

We don't have the struct file * here at btrfs_ioctl_add_dev(), but we have
it in its caller, btrfs_ioctl().

Thanks.

>  	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_DEV_ADD)) {
>  		if (!btrfs_exclop_start_try_lock(fs_info, BTRFS_EXCLOP_DEV_ADD))
>  			return BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
> @@ -3516,6 +3517,7 @@ static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)
>  		btrfs_exclop_balance(fs_info, BTRFS_EXCLOP_BALANCE_PAUSED);
>  	else
>  		btrfs_exclop_finish(fs_info);
> +	sb_end_write(fs_info->sb);
>  	return ret;
>  }
>  
> -- 
> 2.35.1
>