Re: [PATCH 2/2] jbd2: flush filesystem device before updating tail sequence

[Zhang Yi]

On 2024/12/12 20:34, Kemeng Shi wrote:
> 
> 
> on 12/3/2024 3:24 PM, Zhang Yi wrote:
>> On 2024/12/3 14:53, Kemeng Shi wrote:
>>>
>>>
>>> on 12/3/2024 9:44 AM, Zhang Yi wrote:
>>>> From: Zhang Yi <yi.zhang@xxxxxxxxxx>
>>>>
>>>> When committing transaction in jbd2_journal_commit_transaction(), the
>>>> disk caches for the filesystem device should be flushed before updating
>>>> the journal tail sequence. However, this step is missed if the journal
>>>> is not located on the filesystem device. As a result, the filesystem may
>>>> become inconsistent following a power failure or system crash. Fix it by
>>>> ensuring that the filesystem device is flushed appropriately.
>>>>
>>>> Fixes: 3339578f0578 ("jbd2: cleanup journal tail after transaction commit")
>>>> Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
>>>> ---
>>>>  fs/jbd2/commit.c | 4 ++--
>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
>>>> index 4305a1ac808a..f95cf272a1b5 100644
>>>> --- a/fs/jbd2/commit.c
>>>> +++ b/fs/jbd2/commit.c
>>>> @@ -776,9 +776,9 @@ void jbd2_journal_commit_transaction(journal_t *journal)
>>>>  	/*
>>>>  	 * If the journal is not located on the file system device,
>>>>  	 * then we must flush the file system device before we issue
>>>> -	 * the commit record
>>>> +	 * the commit record and update the journal tail sequence.
>>>>  	 */
>>>> -	if (commit_transaction->t_need_data_flush &&
>>>> +	if ((commit_transaction->t_need_data_flush || update_tail) &&
>>>>  	    (journal->j_fs_dev != journal->j_dev) &&
>>>>  	    (journal->j_flags & JBD2_BARRIER))
>>>>  		blkdev_issue_flush(journal->j_fs_dev);
>>>>
>>> In journal_submit_commit_record(), we will submit commit block with REQ_PREFLUSH
>>> which is supposed to ensure disk cache is flushed before writing commit block.
>>> So I think the current code is fine.
>>> Please correct me if I miss anything.
>>>
>>
>> The commit I/O with REQ_PREFLUSH only flushes 'journal->j_dev', not
>> 'journal->j_fs_dev'. We need to flush journal->j_fs_dev to ensure that all
>> written metadata has been persisted to the filesystem disk, Until then, we
>> cannot update the tail sequence.
> My bad...
> Look good to me. Feel free to add:
> 
> Reviewed-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>

It's fine, thanks for your review.

Cheers,
Yi.