Re: repeated oops under load on SH4 system

[Paul Mundt <lethal@linux-sh.org>]

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.