Re: [PATCH 09/12] ext4: drop s_umount over opening the log device

Jan Kara
2023-08-03T13:26:13Z

On Wed 02-08-23 17:41:28, Christoph Hellwig wrote:
> Just like get_tree_bdev needs to drop s_umount when opening the main
> device, we need to do the same for the ext4 log device to avoid a
> potential lock order reversal with s_unmount for the mark_dead path.
>
> It might be preferable to just drop s_umount over ->fill_super entirely,
> but that will require a fairly massive audit first, so we'll do the easy
> version here first.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> fs/ext4/super.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 193d665813b611..2ccb19d345c6dd 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -5854,7 +5854,10 @@ static journal_t *ext4_get_dev_journal(struct super_block *sb,
> if (WARN_ON_ONCE(!ext4_has_feature_journal(sb)))
> return NULL;
>
> + /* see get_tree_bdev why this is needed and safe */
> + up_write(&sb->s_umount);
> bdev = ext4_blkdev_get(j_dev, sb);
> + down_write(&sb->s_umount);
> if (bdev == NULL)
> return NULL;
>
> --
> 2.39.2
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR