Re: [Bug report] journal data mode trigger panic in jbd2_journal_commit_transaction

[yangerkun <yangerkun@huawei.com>]

在 2020/11/19 21:12, Mauricio Oliveira 写道:
> On Thu, Nov 19, 2020 at 1:25 AM yangerkun <yangerkun@huawei.com> wrote:
>>
>>
>>
>> 在 2020/11/16 21:50, Mauricio Oliveira 写道:
>>> Hi Kun,
>>>
>>> On Sat, Nov 14, 2020 at 5:18 AM yangerkun <yangerkun@huawei.com> wrote:
>>>> While using ext4 with data=journal(3.10 kernel), we meet a problem that
>>>> we think may never happend...
>>> [...]
>>>
>>> Could you please confirm you mean 5.10-rc* kernel instead of 3.10?
>>> (It seems so as you mention a recent commit below.)  Thanks!
>>>
>>>> For now, what I have seen that can dirty buffer directly is
>>>> ext4_page_mkwrite(64a9f1449950 ("ext4: data=journal: fixes for
>>>> ext4_page_mkwrite()")), and runing ext4_punch_hole with keep_size
>>>> /ext4_page_mkwrite parallel can trigger above warning easily.
>>> [...]
>>>
>>>
>>
>> Hi,
>>
>> Sorry for the long delay reply... And thanks a lot for your advise! The
>> bug trigger with a very low probability. So won't trigger with 5.10 can
>> not prove no bug exist in 5.10.
>>
> 
> No worries, and thanks for following up.
> So I understand that the bug report was indeed on 3.10, and 5.10-rcN
> is not yet confirmed.
> 
>> Google a lot and notice that someone before has report the same bug[1].
>> '3b136499e906 ("ext4: fix data corruption in data=journal mode")' seems
>> fix the problem. I will try to understand this, and give a analysis
>> about how to reproduce it!
> 
> Cool, thanks!
> 
>> Thanks,
>> Kun.
> 
> 
> 
Hi,

The follow step can reproduce the bug[1] reported before easily. And the 
bug we meet seems same. Following patch will fix the bug.

3b136499e906 ext4: fix data corruption in data=journal mode
b90197b65518 ext4: use private version of page_zero_new_buffers() for 
data=journal mode


1. mkfs.ext4
2. touch $tofile(ino == 12)
3. touch $fromfile(ino == 13) and write 4k to fromfile and sync

mmap $fromfile 4k
and write 4k
to $tofile

...
generic_perform_write
  ext4_write_begin
   ext4_journal_start
   (trans 1)
  if (ino == 12) sleep for 30s
  ...                           truncate $fromfile
                                to 0
  copied=0,bytes=4k
  ext4_journalled_write_end
   page_zero_new_buffers
    mark_buffer_dirty
   write_end_fn
    ...
    __jbd2_journal_file_buffer
     test_clear_buffer_dirty
     __jbd2_journal_temp_unlink_buffer
   ext4_journal_stop
   (trans 1)
                                                  trans1 commit
                                                  ...
   ext4_truncate_failed_write
    ...
    journal_unmap_buffer
     set_buffer_freed
                                                  forget list
                                                   ...
                                                   clear_buffer_jbddirty
                                                   ...
                                                   J_ASSERT_BH(bh,
                                                   !buffer_dirty(bh))
                                                   ^^^^^^^^^^^^^^^^^
                                                   trigger the bug...



[1]. https://www.spinics.net/lists/linux-ext4/msg56447.html

Thanks,
Kun.