linux-ext4 - Re: [PATCH] jbd2: clear JBD2_ABORT flag before journal_reset to update log tail info when load journal

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Date:   Wed, 2 Dec 2020 20:01:39 +0800
From:   yebin <yebin10@...wei.com>
To:     Likai <li.kai4@....com>, "Theodore Y. Ts'o" <tytso@....edu>,
        Jan Kara <jack@...e.cz>
CC:     "linux-ext4@...r.kernel.org" <linux-ext4@...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

Have you really encountered the problem of file system inconsistency 
caused by non-replay of logs?

(1) if (needs_recovery==0)
      jbd2_journal_wipe will call jbd2_mark_journal_empty to update 
s_start and s_sequence.

(2) if (needs_recovery == 1)
   ext4_fill_super:
......
   if (needs_recovery) {
          ext4_msg(sb, KERN_INFO, "recovery complete");
          ext4_mark_recovery_complete(sb, es);    -->Will update s_start 
and s_sequence
  }
......
   Recently, I encountered the problem of inconsistent file system data, 
which may be
caused by the log not replaying during fsck. But according to the 
description of your
patch, the s_start and the  s_sequence will all be updated.
   Therefore, I doubt whether the problem you described really exists.


On 2020/1/20 14:30, Likai wrote:
> 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
>
> .
>