Re: repeated oops under load on SH4 system

Paul Mundt
2008-11-10T08:11:59Z

On Mon, Nov 10, 2008 at 05:06:23PM +0900, Paul Mundt wrote:
> On Tue, Nov 04, 2008 at 09:31:44PM +0900, CHIKAMA Masaki wrote:
> > Hello all.
> >
> > I've got repeated oops message under a load on kernel 2.6.26.7.
> > It happens once or twice per a week with the below message.
> >
> > >Unable to handle kernel paging request at virtual address dfff0700
> > >Unable to handle kernel paging request at virtual address dfff1000
> > >Unable to handle kernel paging request at virtual address dfff0a00
> >
> > I have been gotten this message from around kernel 2.6.23. I didn't
> > test before it.
> > My hardware is mach-landisk with attached .config.
> > The root file system is on nfs server.
> > Please let me know if you need more information to investigating the problem.
> > Could somebody give me a hint to resolve the issue ?
> >
> > Thanks in advance.
> >
> This suggests you are getting a TLB miss on various fixmap entries. Based
> on your call chain, these are related to the cache colouring in the page
> copying. update_mmu_cache() specifically faults the translation in, so
> you should not be making it all the way up to the TLB miss handler in the
> first place. This points to something evicting the entry from the TLB
> during your copy, which while it is not something I have seen in
> practice, is interesting to know that it remains a possibility under
> other workloads. A simple but expensive fix for this would be blowing out
> the TLB and speculatively bumping up the UTLB replace boundary prior to
> pre-faulting the fixmap translation. I'll look at this some more over the
> next couple days and send you a patch for testing.

Now I remember where I saw this before.. try this patch:

http://marc.info/?l=linux-sh&m\x120400865707505&w=2

There was never any feedback on it, and I was not able to reproduce the
issues.