Re: patchmm-fix-committed_as-underflow-on-large-nr_cpus-environment.patchadded to 2.6.29-stable tree

[Greg KH]

On Wed, May 06, 2009 at 07:26:51AM +0900, KOSAKI Motohiro wrote:
> 2009/5/6 Greg KH <gregkh@xxxxxxx>:
> > On Tue, May 05, 2009 at 08:36:19PM +0200, Stefan Lippers-Hollmann wrote:
> >> Hi
> >>
> >> On Dienstag, 5. Mai 2009, gregkh@xxxxxxx wrote:
> >> [...]
> >> > From 00a62ce91e554198ef28234c91c36f850f5a3bc9 Mon Sep 17 00:00:00 2001
> >> > From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> >> > Date: Thu, 30 Apr 2009 15:08:51 -0700
> >> > Subject: mm: fix Committed_AS underflow on large NR_CPUS environment
> >> >
> >> > From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> >> >
> >> > commit 00a62ce91e554198ef28234c91c36f850f5a3bc9 upstream.
> >> >
> >> > The Committed_AS field can underflow in certain situations:
> >> >
> >> > >         # while true; do cat /proc/meminfo  | grep _AS; sleep 1; done | uniq -c
> >> > >               1 Committed_AS: 18446744073709323392 kB
> >> > >              11 Committed_AS: 18446744073709455488 kB
> >> > >               6 Committed_AS:    35136 kB
> >> > >               5 Committed_AS: 18446744073709454400 kB
> >> > >               7 Committed_AS:    35904 kB
> >> > >               3 Committed_AS: 18446744073709453248 kB
> >> > >               2 Committed_AS:    34752 kB
> >> > >               9 Committed_AS: 18446744073709453248 kB
> >> > >               8 Committed_AS:    34752 kB
> >> > >               3 Committed_AS: 18446744073709320960 kB
> >> > >               7 Committed_AS: 18446744073709454080 kB
> >> > >               3 Committed_AS: 18446744073709320960 kB
> >> > >               5 Committed_AS: 18446744073709454080 kB
> >> > >               6 Committed_AS: 18446744073709320960 kB
> >> >
> >> > Because NR_CPUS can be greater than 1000 and meminfo_proc_show() does
> >> > not check for underflow.
> >> >
> >> > But NR_CPUS proportional isn't good calculation.  In general,
> >> > possibility of lock contention is proportional to the number of online
> >> > cpus, not theorical maximum cpus (NR_CPUS).
> >> >
> >> > The current kernel has generic percpu-counter stuff.  using it is right
> >> > way.  it makes code simplify and percpu_counter_read_positive() don't
> >> > make underflow issue.
> >>
> >> This patch reproducably panics on all systems I could test so far on
> >> 2.6.29.2 + the current stable queue:
> >> - Acer Aspire One, Intel Atom N270, Intel 945GC chipset (i386)
> >> - AMD64 3200+, nVidia nforce3 chipset (amd64)
> >> - AMD64 X2 4200+, nVidia nforce4 chipset (amd64)
> >>
> >> Kernel panic (sorry, this is from a bad webcam and only the last part of
> >> the messages scrolling by - I can try to get a serial console tomorrow),
> >> taken from an AMD64 3200+, nVidia nforce3 chipset (amd64).
> >> http://sidux.com/slh/mm-fix-committed_as-underflow-on-large-nr_cpus-environment/panic.gif [198 KB]
> >>
> >> Reverting just this patch fixes the problem for me.
> >>
> >> Kernel configurations:
> >> http://sidux.com/slh/mm-fix-committed_as-underflow-on-large-nr_cpus-environment/config-2.6.29-2.slh.5.3-sidux-686   [96 KB]
> >> http://sidux.com/slh/mm-fix-committed_as-underflow-on-large-nr_cpus-environment/config-2.6.29-2.slh.5.6-sidux-amd64 [91 KB]
> >
> > Yes, I just confirmed this on my machines as well, so I'm going to drop
> > it from the stable queue.
> >
> > If anyone thinks it is really necessary for the 2.6.29-stable tree,
> > please resubmit it after fixing it and testing that it works :)
> >
> > thanks,
> 
> Could you please post oops log?
> current mmotm (include this patch) works fine on my x86_64 box. Then,
> I have no hint now ;-)

Ok, I'll apply the patch and reboot and take a picture of it...

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