linux-kernel - Re: 2.6.18 ext3 panic.

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Date:	Mon, 09 Oct 2006 14:59:25 -0700
From:	Badari Pulavarty <pbadari@...ibm.com>
To:	Eric Sandeen <sandeen@...deen.net>
Cc:	Andrew Morton <akpm@...l.org>, Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	esandeen@...hat.com, Jan Kara <jack@....cz>
Subject: Re: 2.6.18 ext3 panic.

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@...deen.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



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