Re: 2.6.18 ext3 panic.

Badari Pulavarty
2006-10-09T21:59:52Z

On Mon, 2006-10-09 at 14:46 -0500, Eric Sandeen wrote:
> Andrew Morton wrote:
> > On Tue, 03 Oct 2006 00:43:01 -0500
> > Eric Sandeen <sandeen@sandeen.net> wrote:
> >
> >> Dave Jones wrote:
> >>
> >>> So I managed to reproduce it with an 'fsx foo' and a
> >>> 'fsstress -d . -r -n 100000 -p 20 -r'. This time I grabbed it from
> >>> a vanilla 2.6.18 with none of the Fedora patches..
> >>>
> >>> I'll give 2.6.18-git a try next.
> >>>
> >>> Dave
> >>>
> >>> ----------- [cut here ] --------- [please bite here ] ---------
> >>> Kernel BUG at fs/buffer.c:2791
> >> I had thought/hoped that this was fixed by Jan's patch at
> >> http://lkml.org/lkml/2006/9/7/236 from the thread started at
> >> http://lkml.org/lkml/2006/9/1/149, but it seems maybe not. Dave hit this bug
> >> first by going through that new codepath....
> >
> > Yes, Jan's patch is supposed to fix that !buffer_mapped() assertion. iirc,
> > Badari was hitting that BUG and was able to confirm that Jan's patch
> > (3998b9301d3d55be8373add22b6bc5e11c1d9b71 in post-2.6.18 mainline) fixed
> > it.
>
> Looking at some BH traces*, it appears that what Dave hit is a truncate
> racing with a sync...
>
> truncate ...
> ext3_invalidate_page
> journal_invalidatepage
> journal_unmap buffer
>
> going off at the same time as
>
> sync ...
> journal_dirty_data
> sync_dirty_buffer
> submit_bh <-- finds unmapped buffer, boom.
>

I don't understand how this can happen ..

journal_unmap_buffer() zapping the buffer since its not attached to any
transaction.

journal_unmap_buffer():[fs/jbd/transaction.c:1789] not on any
transaction: zap
b_state:0x10402f b_jlist:BJ_None cpu:0 b_count:3 b_blocknr:52735707
b_jbd:1 b_frozen_data:0000000000000000
b_committed_data:0000000000000000
b_transaction:0 b_next_transaction:0 b_cp_transaction:0
b_trans_is_running:0
b_trans_is_comitting:0 b_jcount:2 pg_dirty:1

journal_dirty_data() would do submit_bh() ONLY if its part of the older
transaction.

I need to take a closer look to understand the race.

BTW, is this 1k or 2k filesystem ? How easy is to reproduce the
problem ?

Thanks,
Badari