Re: [PATCH] tests/xfs: test for NULL xattr buffer problem during unlink

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Oct 13, 2017 at 06:08:39AM -0400, Brian Foster wrote:
> On Fri, Oct 13, 2017 at 01:46:05PM +0800, Eryu Guan wrote:
> > On Thu, Oct 12, 2017 at 07:36:27AM -0400, Brian Foster wrote:
> > > XFS had a bug that resulted in an unexpected NULL buffer during
> > > unlink of an inode with a multi-level attr fork tree. This occurred
> > > due to a stale reference to content in a released/reclaimed buffer.
> > > 
> > > Use the XFS buffer LRU reference count error injection tag to
> > > recreate the conditions for the bug. Create a file with a
> > > multi-level attr fork tree and then unlink it with buffer caching
> > > disabled.
> > > 
> > > Signed-off-by: Brian Foster <bfoster@redhat.com>
> > > ---
> > > 
> > > Note that this test depends on a pending[1] XFS error injection tag.
> > > 
> > > Brian
> > > 
> > > [1] https://marc.info/?l=linux-xfs&m=150765408521029&w=2
> > 
> > I ran this test with above patch applied (v4.14-rc4 based), and kernel
> > crashed as expected. Then cherry-pick commit f35c5e10c6ed ("xfs: reinit
> > btree pointer on attr tree inactivation walk") and test passed. So test
> > looks good to me, just that I added 'dangerous' group and referenced the
> > fix in commit log and test description.
> > 
> 
> I don't think dangerous is really necessary because this test won't run
> on any kernels prior to those with the patch above, which is still
> pending, and the crash issue had already been addressed in commit
> cd87d8679 ("xfs: don't crash on unexpected holes in dir/attr btrees").

Waitaminute, cd87d8679 went in 4.13-rc1, so any 4.14 should not crash.
What backtrace did you see?

--D

> There is technically a crash possibility for custom kernels that
> backport the later errortag patch without the earlier crash/corruption
> fix, as you have for testing purposes. I think that is out of the
> ordinary and doesn't really justify tagging the test, IMO.
> 
> Brian
> 
> > Thanks for the test!
> > 
> > Eryu
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