Re: [PATCH v3 0/2] fix error flag covered by journal recovery

[Baokun Li <libaokun1@huawei.com>]

On 2023/2/14 10:29, Ye Bin wrote:
> From: Ye Bin <yebin10@huawei.com>
>
> Diff v3 Vs v2:
> Only fix fs error flag lost when previous journal errno is not record
> in disk. As this may lead to drop orphan list, however fs not record
> error flag, then fsck will not repair deeply.
>
> Diff v2 vs v1:
> Move call 'j_replay_prepare_callback' and 'j_replay_end_callback' from
> ext4_load_journal() to jbd2_journal_recover().
>
> When do fault injection test, got issue as follows:
> EXT4-fs (dm-5): warning: mounting fs with errors, running e2fsck is recommended
> EXT4-fs (dm-5): Errors on filesystem, clearing orphan list.
> EXT4-fs (dm-5): recovery complete
> EXT4-fs (dm-5): mounted filesystem with ordered data mode. Opts: data_err=abort,errors=remount-ro
>
> EXT4-fs (dm-5): recovery complete
> EXT4-fs (dm-5): mounted filesystem with ordered data mode. Opts: data_err=abort,errors=remount-ro
>
> Without do file system check, file system is clean when do second mount.
> Theoretically, the kernel will not clear fs error flag. In errors=remount-ro
> mode the last super block is commit directly. So super block in journal is
> not uptodate. When do jounral recovery, the uptodate super block will be
> covered by jounral data. If super block submit all failed after recover
> journal, then file system error flag is lost. When do "fsck -a" couldn't
> repair file system deeply.
> To solve above issue we need to do extra handle when do super block journal
> recovery.
>
>
> Ye Bin (2):
>    ext4: commit super block if fs record error when journal record
>      without error
>    ext4: make sure fs error flag setted before clear journal error
>
>   fs/ext4/super.c | 18 ++++++++++++++++--
>   1 file changed, 16 insertions(+), 2 deletions(-)
When we proceed in the flow of ( uninstall after injecting fault 
triggered error -> mount
kernel replay journal -> umount to view fsck info ), there are three cases:

1. When an injection fault causes the ERROR_FS flag to not be saved to 
disk, but j_errno
is successfully saved to disk, PATCH 2/2 effectively ensures that 
ERROR_FS is saved to disk
so that fsck performs a force check to discover the error correctly.

2. When j_errno is lost and the ERROR_FS flag is saved, after the 
journal replay：
     a. The ext4_super_block on disk has neither error info nor ERROR_FS 
flag;
     b. The ext4_super_block in memory contains error info but no 
ERROR_FS flag
         because the error info is copied additionally during journal 
replay;
     c. The ext4_sb_info in memory contains both error info and ERROR_FS 
flag.
This means that the ext4_super_block in memory will be written to disk 
the next time
ext4_commit_super is executed, while the ERROR_FS flag in ext4_sb_info 
will not be written
to disk until ext4_put_super is called. So if there is a disk 
deletion/power failure/disk offline,
we will lose the ERROR_FS flag or even the error info.

(In this case, repairing directly with e2fsck will not do a force check 
either, because it
relies on j_errno to recover the ERROR_FS flag after the journal replay. 
And it reloads
the information from the disk into memory after the journal replay, so the
ERROR_FS flag and error info are completely lost.)

3. If neither the ERROR_FS flag nor j_errno are saved to disk, we seem 
to be unable to
determine if a deep sweep is currently needed. But I think when journal 
replay is needed
it means that the file system exits abnormally,
*Is it possible to consider e2fsck to do a force check after the journal 
replay?*

-- 
With Best Regards,
Baokun Li
.