On Sat, Jan 12, 2019 at 05:32:21PM +0800, zhangyi (F) wrote:
> On 2019/1/12 15:39, Eryu Guan Wrote:
> > On Thu, Jan 10, 2019 at 02:12:02PM +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 when writing
> >> cached pages later, such as during umount time.
> >>
> >> This patch mark buffer as freed 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).
> >
> > Would you please capture the fsx ops sequences that could reproduce the
> > problem and replay it in a targeted regression test, like what
> > generic/{499,511} do? Thanks!
> >
>
> Yes, I will do it. But this problem is timing dependent, so I am afraid
> this targeted regression test cannot always reproduce it (not even
> generic/455 with above seeds).
That's fine, if there're multiple sequences could reproduce the bug, we
could replay them all in a test.
>
> BTW, we only test and capture this problem on ext4, I am not sure other
> file systems have the same problem or not. So better to categorize this
> test to tests/ext4 group?
If there's nothing specific to ext4, a generic test would be fine.
Thanks!
Eryu
