linux-kernel - Re: 2.6.18 ext3 panic.

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Date:	Mon, 16 Oct 2006 18:54:11 +0200
From:	Jan Kara <jack@...e.cz>
To:	Eric Sandeen <esandeen@...hat.com>
Cc:	Badari Pulavarty <pbadari@...ibm.com>,
	Andrew Morton <akpm@...l.org>,
	Eric Sandeen <sandeen@...deen.net>,
	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.18 ext3 panic.

> Jan Kara wrote:
> 
> >> This is exactly  the solution I proposed earlier (to check 
> >> buffer_mapped() before calling submit_bh()).
> >> But at that time, Jan pointed out that the whole handling is wrong.
> >   Yes, and it was. However it turned out that there are more problems
> > than I thought ;).
> > 
> >> But if this is the only case we need to handle, I am okay with this band 
> >> aid :)
> >   I think Eric's patch may be a part of it. But we still need to check whether
> > the buffer is not after EOF before submitting it (or better said just
> > after we manage to lock the buffer). Because while we are waiting for
> > the buffer lock, journal_unmap_buffer() can still come and steal the
> > buffer - at least the write-out in journal_dirty_data() definitely needs
> > the check if I haven't overlooked something.
> 
> Ok, let me think on that today.  My first reaction is that if we have
> the bh state lock and pay attention to mapped in journal_dirty_data(),
> then any blocks past EOF which have gotten unmapped by
> journal_unmap_buffer will be recognized as such (because they are now
> unmapped... without needing to check for past EOF...) and we'll be fine.
  Hmm, yes, you're right. If we do the test in journal_dirty_data() we
should not file unmapped buffer into transaction's list and hence we
should be safe. Fine. In case we eventually hit the assertion, we can
think further ;).

> As a datapoint, davej's stresstest (several fsx's and fsstresses)
> survived an overnight run on his box, which used to panic in < 2 hrs.
> Survived about 6 hours on my box until I intentionally stopped it; my
> box had added a write/truncate test in a loop, with a bunch of periodic
> syncs as well....
  Perfect :).

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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