linux-ext4 - Re: [PATCH v2 0/6] fix error flag covered by journal recovery

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Date:   Fri, 10 Feb 2023 12:56:28 +0100
From:   Jan Kara <jack@...e.cz>
To:     Ye Bin <yebin@...weicloud.com>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        jack@...e.cz, Ye Bin <yebin10@...wei.com>
Subject: Re: [PATCH v2 0/6] fix error flag covered by journal recovery

Hello!

On Fri 10-02-23 11:20:38, Ye Bin wrote:
> From: Ye Bin <yebin10@...wei.com>
> 
> 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.

Thanks for the patches. Looking through the patches, I think this is a bit
of an overengineering for the problem at hand. The only thing that is
really worth preserving so that it is not lost after journal replay is the
error information. So in ext4_load_journal() I would just save that if
EXT4_ERROR_FS is set in es->s_state before journal replay and restore it
after journal replay. Sure if the superblock write during journal replay
succeeds but the write restoring the error information fails, we will loose
the error information but that is so unlikely in practice that I don't
think it is really worth complicating the code for it. Also the only
downside is we will loose the information there is some error in the
filesystem - we'll soon find that out again anyway :).

								Honza

> 
> Ye Bin (6):
>   jbd2: introduce callback for recovery journal
>   ext4: introudce helper for jounral recover handle
>   jbd2: do extra handle when do journal recovery
>   ext4: remove backup for super block when recovery journal
>   ext4: fix super block checksum error
>   ext4: make sure fs error flag setted before clear journal error
> 
>  fs/ext4/ext4_jbd2.c  | 66 ++++++++++++++++++++++++++++++++++++++++++++
>  fs/ext4/ext4_jbd2.h  |  2 ++
>  fs/ext4/super.c      | 18 ++++--------
>  fs/jbd2/recovery.c   | 27 ++++++++++++++++++
>  include/linux/jbd2.h | 11 ++++++++
>  5 files changed, 112 insertions(+), 12 deletions(-)
> 
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR