linux-kernel - Re: [PATCH] jbd2: clear JBD2_ABORT flag before journal_reset to update log tail info when load journal

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Message-ID: <20200117212657.GF448999@mit.edu>
Date:   Fri, 17 Jan 2020 16:26:57 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     Kai Li <li.kai4@....com>, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, joseph.qi@...ux.alibaba.com,
        gechangwei@...e.cn, wang.yongd@....com, wang.xibo@....com
Subject: Re: [PATCH] jbd2: clear JBD2_ABORT flag before journal_reset to
 update log tail info when load journal

On Tue, Jan 14, 2020 at 11:31:19AM +0100, Jan Kara wrote:
> Thanks for the patch! Just some small comments below:
> 
> On Sat 11-01-20 10:25:42, Kai Li wrote:
> > Fixes: 85e0c4e89c1b "jbd2: if the journal is aborted then don't allow update of the log tail"
> 
> This tag should come at the bottom of the changelog (close to your
> Signed-off-by).
> 
> > If journal is dirty when mount, it will be replayed but jbd2 sb
> > log tail cannot be updated to mark a new start because
> > journal->j_flags has already been set with JBD2_ABORT first
> > in journal_init_common.
> > When a new transaction is committed, it will be recorded in block 1
> > first(journal->j_tail is set to 1 in journal_reset). If emergency
> > restart again before journal super block is updated unfortunately,
> > the new recorded trans will not be replayed in the next mount.
> > It is danerous which may lead to metadata corruption for file system.
> 
> I'd slightly rephrase the text here so that it is more easily readable and
> correct some grammar mistakes. Something like:
> 
> If the journal is dirty when the filesystem is mounted, jbd2 will replay
> the journal but the journal superblock will not be updated by
> journal_reset() because JBD2_ABORT flag is still set (it was set in
> journal_init_common()). This is problematic because when a new transaction
> is then committed, it will be recorded in block 1 (journal->j_tail was set
> to 1 in journal_reset()). If unclean shutdown happens again before the
> journal superblock is updated, the new recorded transaction will not be
> replayed during the next mount (because of stale sb->s_start and
> sb->s_sequence values) which can lead to filesystem corruption.
> 
> Otherwise the patch looks good to me so feel free to add:
> 
> Reviewed-by: Jan Kara <jack@...e.cz>
> 
> (again this is added to the bottom of the changelog like the 'Fixes' tag or
> 'Signed-off-by' tag).

Thanks, applied with a fixed up commit description.

		       	     	       - Ted