Re: ia64 hang/mca running gdb 'make check'

[Hugh Dickins]

On Tue, 20 Jul 2010, dann frazier wrote:
> On Wed, Jul 21, 2010 at 10:51:36AM +0900, KAMEZAWA Hiroyuki wrote:
> > On Tue, 20 Jul 2010 11:35:12 -0600
> > dann frazier <dannf@xxxxxxxxxx> wrote:
> > 
> > > Debian's ia64 autobuilders have been experiencing system crashes while
> > > trying to run the gdb test suite:
> > >   http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=588574
> > > 
> > > I was able to reproduce this w/ the latest git tree, and bisected it
> > > down to this commit, introduced in 2.6.32:
> > > 
> > >   commit 62eede62dafb4a6633eae7ffbeb34c60dba5e7b1
> > >   Author: Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx>
> > >   Date:   Mon Sep 21 17:03:34 2009 -0700
> > > 
> > >     mm: ZERO_PAGE without PTE_SPECIAL
> > > 
> > >     Reinstate anonymous use of ZERO_PAGE to all architectures, not just to
> > >     those which __HAVE_ARCH_PTE_SPECIAL: as suggested by Nick Piggin.
> > > 
> > >     Contrary to how I'd imagined it, there's nothing ugly about this, just a
> > >     zero_pfn test built into one or another block of vm_normal_page().
> > > 
> > >     But the MIPS ZERO_PAGE-of-many-colours case demands is_zero_pfn() and
> > >     my_zero_pfn() inlines.  Reinstate its mremap move_pte() shuffling of
> > >     ZERO_PAGEs we did from 2.6.17 to 2.6.19?  Not unless someone shouts for
> > >     that: it would have to take vm_flags to weed out some cases.
> > > 
> > > fyi, I found this to not be reproducible on SLES11 SP1 (which is
> > > 2.6.32-based). I compared the .configs and found that the relevant
> > > difference is the PAGE_SIZE. It does not fail w/ 64KB pages, but
> > > reliably fails w/ 16KB pages.
> > > 
> > 
> > Sorry, I have no idea...
> > Hmm, what is the address of empty_zero_page[] on your debian(16kb-page) ?
> 
> 
> dannf@krebs:~$ grep empty_zero_page /boot/System.map-2.6.32-5-mckinley 
> a0000001008784c0 d __ksymtab_empty_zero_page
> a000000100882688 d __kcrctab_empty_zero_page
> a000000100884ca4 r __kstrtab_empty_zero_page
> a000000100974000 D empty_zero_page

Thanks a lot for reporting this, but I too have no idea yet.

It is likely that the bug is not to be found in that 62eede62, but
rather in one of the preceding patches to mm/memory.c which 62eede62
was extending to ia64 and other architectures without PTE_SPECIAL.

I wonder, from looking at that gdb testsuite log, is it plausible
that all these hangs/crashes occurred when writing out a coredump?
Is that something you could check for us? or rule out the possibility.

I was rather proud of the get_dump_page() simplification,
but perhaps there's something nasty lurking in there.

Hugh
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