Re: [PATCH RFC 03/28] ext2: don't set SB_RDONLY after filesystem errors

[sashiko-bot@kernel.org]

> When ext2 is mounted with errors=remount-ro ext2_error() sets SB_RDONLY.
> It does that without holding sb->s_umount and from whatever context
> found the error. That includes a frozen filesystem. FIFREEZE doesn't
> block reads so a lookup in a corrupted directory is enough to get there.
> 
> That's a problem because freeze_super() and thaw_super() both look at
> sb_rdonly() to figure out whether the s_writers rwsems need to be taken
> or released. A read-only superblock is frozen without taking them. So if
> SB_RDONLY gets set while the filesystem is frozen thaw_super() takes the
> read-only shortcut, skips ->unfreeze_fs() and sb_freeze_unlock() and
> marks the superblock unfrozen with all three rwsems still write-locked.
> Every writer after that blocks forever in sb_start_write():
> 
>   EXT2-fs (vda): error: ext2_check_folio: bad entry in directory #12: : rec_len is smaller than minimal - offset=24, inode=13, rec_len=0, name_len=1
>   EXT2-fs (vda): error: remounting filesystem read-only
> [ ... ]
> [1]: https://lore.kernel.org/r/hyhuckyohsabx2suvq3z7uy3pbgmihva6wgzxr3op7pzcrlu33@p7zzlgp2ehjf
> 
> Reported-by: Karl Mehltretter <kmehltretter@gmail.com>
> Link: https://lore.kernel.org/r/20260903060855.4610-1-kmehltretter@gmail.com
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20261012-work-fs-sb_rdonly-v1-0-60743a3dc326@kernel.org?part=3