linux-ext4 - Re: [PATCH] [RFC] Fix data missing when reusing bh which is ready to be checkpointed

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Date:   Sat, 7 Jan 2023 17:28:54 +0800
From:   Zhihao Cheng <chengzhihao1@...wei.com>
To:     Jan Kara <jack@...e.cz>
CC:     <tytso@....edu>, <jack@...e.com>, <linux-ext4@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>,
        <libaokun1@...wei.com>, <zhanchengbin1@...wei.com>,
        <yangerkun@...wei.com>
Subject: Re: [PATCH] [RFC] Fix data missing when reusing bh which is ready to
 be checkpointed

在 2022/12/21 18:13, Jan Kara 写道:
> On Tue 20-12-22 23:05:51, Zhihao Cheng wrote:
>> From: zhanchengbin <zhanchengbin1@...wei.com>
>>
>> Following process will make data lost and could lead to a filesystem
>> corrupted problem:
>>
>> 1. jh(bh) is inserted into T1->t_checkpoint_list, bh is dirty, and
>>     jh->b_transaction = NULL
>> 2. T1 is added into journal->j_checkpoint_transactions.
>> 3. Get bh prepare to write while doing checkpoing:
>>             PA				    PB
>>     do_get_write_access             jbd2_log_do_checkpoint
>>      spin_lock(&jh->b_state_lock)
>>       if (buffer_dirty(bh))
>>        clear_buffer_dirty(bh)   // clear buffer dirty
>>         set_buffer_jbddirty(bh)
>> 				    transaction =
>> 				    journal->j_checkpoint_transactions
>> 				    jh = transaction->t_checkpoint_list
>> 				    if (!buffer_dirty(bh))
>> 		                      __jbd2_journal_remove_checkpoint(jh)
>> 				      // bh won't be flushed
>> 		                    jbd2_cleanup_journal_tail
>>      __jbd2_journal_file_buffer(jh, transaction, BJ_Reserved)
>> 4. Aborting journal/Power-cut before writing latest bh on journal area.

[...]
>>
>>   fs/jbd2/transaction.c | 8 ++++++--
>>   1 file changed, 6 insertions(+), 2 deletions(-)
> 
> Good catch! Did you find it by code inspection or were you able to actually
> trigger this problem?

By code inspection.
Reproducer: https://bugzilla.kernel.org/show_bug.cgi?id=216898