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

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Date:   Mon, 20 Jan 2020 06:30:33 +0000
From:   Likai <li.kai4@....com>
To:     "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>
CC:     "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "joseph.qi@...ux.alibaba.com" <joseph.qi@...ux.alibaba.com>,
        "gechangwei@...e.cn" <gechangwei@...e.cn>,
        Wangyong <wang.yongD@....com>, Wangxibo <wang.xibo@....com>
Subject: Re: [PATCH] jbd2: clear JBD2_ABORT flag before journal_reset to
 update log tail info when load journal

On 2020/1/18 5:27, Theodore Y. Ts'o wrote:
> 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
>
Sorry for reply so late due to my business trip recently.  This new
comment is ok and more clear. Thanks.

                                                                       
                                                                       
      - Kai