[syzbot] [erofs?] [fat?] WARNING in erofs_kill_sb

[Gao Xiang]

On 2023/7/31 17:37, Christoph Hellwig wrote:
> On Mon, Jul 31, 2023 at 12:57:58AM -0700, syzbot wrote:
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit:    d7b3af5a77e8 Add linux-next specific files for 20230728
> 
> Hmm, the current linux-next tree does not seem to have that commit ID
> any more, and the line numbers don't match up.  I think it is the
> WARN_ON for the magic, which could probably be just removed.  I'll
> try the reproducers when I find a bit more time.

Previously, deactivate_locked_super() or .kill_sb() will only be
called after fill_super is called, and .s_magic will be set at
the very beginning of erofs_fc_fill_super().

After ("fs: open block device after superblock creation"), such
convension is changed now.  Yet at a quick glance,

WARN_ON(sb->s_magic != EROFS_SUPER_MAGIC);

in erofs_kill_sb() can be removed since deactivate_locked_super()
will also be called if setup_bdev_super() is falled.  I'd suggest
that removing this WARN_ON() in the related commit, or as
a following commit of the related branch of the pull request if
possible.

Thanks,
Gao Xiang