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

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在 2020/11/19 21:12, Mauricio Oliveira 写道:
On Thu, Nov 19, 2020 at 1:25 AM yangerkun <yangerkun@xxxxxxxxxx> wrote:



在 2020/11/16 21:50, Mauricio Oliveira 写道:
Hi Kun,

On Sat, Nov 14, 2020 at 5:18 AM yangerkun <yangerkun@xxxxxxxxxx> 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.



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