Re: 2.6.18 ext3 panic.

Jan Kara
2006-10-16T16:54:00Z

> 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@suse.cz>
SuSE CR Labs