linux-ext4 - Re: [PATCH v4 1/4] jbd2: make sure dirty flag is cleared while revorking a buffer which belongs to older transaction

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Message-ID: <bb69d5d1-662f-7653-0dfe-91e0c763c9e3@huawei.com>
Date:   Tue, 12 Feb 2019 20:20:42 +0800
From:   "zhangyi (F)" <yi.zhang@...wei.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>
CC:     <linux-ext4@...r.kernel.org>, <jack@...e.cz>,
        <adilger.kernel@...ger.ca>, <miaoxie@...wei.com>
Subject: Re: [PATCH v4 1/4] jbd2: make sure dirty flag is cleared while
 revorking a buffer which belongs to older transaction

On 2019/2/11 12:24, Theodore Y. Ts'o Wrote:
> On Wed, Jan 30, 2019 at 02:49:37PM +0800, zhangyi (F) wrote:
>> Now, we capture a data corruption problem on ext4 while we're truncating
>> an extent index block. Imaging that if we are revoking a buffer which
>> has been journaled by the committing transaction, the buffer's jbddirty
>> flag will not be cleared in jbd2_journal_forget(), so the commit code
>> will set the buffer dirty flag again after refile the buffer.
>>
>> fsx                               kjournald2
>>                                   jbd2_journal_commit_transaction
>> jbd2_journal_revoke                commit phase 1~5...
>>  jbd2_journal_forget
>>    belongs to older transaction    commit phase 6
>>    jbddirty not clear               __jbd2_journal_refile_buffer
>>                                      __jbd2_journal_unfile_buffer
>>                                       test_clear_buffer_jbddirty
>>                                        mark_buffer_dirty
>>
>> Finally, if the freed extent index block was allocated again as data
>> block by some other files, it may corrupt the file data after writing
>> cached pages later, such as during unmount time. (In general,
>> clean_bdev_aliases() related helpers should be invoked after
>> re-allocation to prevent the above corruption, but unfortunately we
>> missed it when zeroout the head of extra extent blocks in
>> ext4_ext_handle_unwritten_extents()).
>>
>> This patch mark buffer as freed and set j_next_transaction to the new
>> transaction when it already belongs to the committing transaction in
>> jbd2_journal_forget(), so that commit code knows it should clear dirty
>> bits when it is done with the buffer.
>>
>> This problem can be reproduced by xfstests generic/455 easily with
>> seeds (3246 3247 3248 3249).
>>
>> Signed-off-by: zhangyi (F) <yi.zhang@...wei.com>
>> Reviewed-by: Jan Kara <jack@...e.cz>
>> Cc: stable@...r.kernel.org
> 
> Thanks, applied.
> 
> By the way, I wasn't able to easily reproduce the problem using the
> given seeds.  Out of curiosity, what sort test system were you using?
> (e.g., how many CPU's, how much memory, what kind of storage device,
> etc.)

Yes, I was also not able to reproduce the problem quite easily, because
it depends on block allocation logic. So in order to increase the
probability, I choice a relatively small prartition(5GB).

I reprocude this problem on a x86_64 kvm virtual machine which have 16
cores, 16GB memory and two 5GB virtio block devices(base on ssd RIAD).

Thanks,
Yi.