linux-kernel - Re: Linux 2.6.25-rc2

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Date:	Tue, 19 Feb 2008 09:21:27 +0200
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Torsten Kaiser" <just.for.lkml@...glemail.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Mathieu Desnoyers" <mathieu.desnoyers@...ymtl.ca>,
	"Christoph Lameter" <clameter@....com>
Subject: Re: Linux 2.6.25-rc2

On Feb 19, 2008 8:54 AM, Torsten Kaiser <just.for.lkml@...glemail.com> wrote:
> > > [ 5282.056415] ------------[ cut here ]------------
> > > [ 5282.059757] kernel BUG at lib/list_debug.c:33!
> > > [ 5282.062055] invalid opcode: 0000 [1] SMP
> > > [ 5282.062055] CPU 3
> >
> > hm. Your crashes do seem to span multiple subsystems, but it always
> > seems to be around the SLUB code. Could you try the patch below? The
> > SLUB code has a new optimization and i'm not 100% sure about it. [the
> > hack below switches the SLUB optimization off by disabling the CPU
> > feature it relies on.]
> >
> >         Ingo
> >
> > ------------->
> >  arch/x86/Kconfig |    4 ----
> >  1 file changed, 4 deletions(-)
> >
> > Index: linux/arch/x86/Kconfig
> > ===================================================================
> > --- linux.orig/arch/x86/Kconfig
> > +++ linux/arch/x86/Kconfig
> > @@ -59,10 +59,6 @@ config HAVE_LATENCYTOP_SUPPORT
> >  config SEMAPHORE_SLEEPERS
> >         def_bool y
> >
> > -config FAST_CMPXCHG_LOCAL
> > -       bool
> > -       default y
> > -
> >  config MMU
> >         def_bool y
> >
>
> $ grep FAST_CMPXCHG_LOCAL */.config
> linux-2.6.24-rc2-mm1/.config:CONFIG_FAST_CMPXCHG_LOCAL=y
> linux-2.6.24-rc3-mm1/.config:CONFIG_FAST_CMPXCHG_LOCAL=y
> linux-2.6.24-rc3-mm2/.config:CONFIG_FAST_CMPXCHG_LOCAL=y
> linux-2.6.24-rc6-mm1/.config:CONFIG_FAST_CMPXCHG_LOCAL=y
> linux-2.6.24-rc8-mm1/.config:CONFIG_FAST_CMPXCHG_LOCAL=y
> linux-2.6.25-rc1/.config:CONFIG_FAST_CMPXCHG_LOCAL=y
> linux-2.6.25-rc2-mm1/.config:CONFIG_FAST_CMPXCHG_LOCAL=y
> linux-2.6.25-rc2/.config:CONFIG_FAST_CMPXCHG_LOCAL=y
>
> -rc2-mm1 still worked for me.
>
> Did you mean the new SLUB_FASTPATH?
> $ grep "define SLUB_FASTPATH" */mm/slub.c
> linux-2.6.25-rc1/mm/slub.c:#define SLUB_FASTPATH
> linux-2.6.25-rc2-mm1/mm/slub.c:#define SLUB_FASTPATH
> linux-2.6.25-rc2/mm/slub.c:#define SLUB_FASTPATH
>
> The 2.6.24-rc3+ mm-kernels did crash for me, but don't seem to contain this...
>
> On the other hand:
> From the crash in 2.6.25-rc2-mm1:
> [59987.116182] RIP  [<ffffffff8029f83d>] kmem_cache_alloc_node+0x6d/0xa0
>
> (gdb) list *0xffffffff8029f83d
> 0xffffffff8029f83d is in kmem_cache_alloc_node (mm/slub.c:1646).
> 1641                    if (unlikely(is_end(object) || !node_match(c, node))) {
> 1642                            object = __slab_alloc(s, gfpflags,
> node, addr, c);
> 1643                            break;
> 1644                    }
> 1645                    stat(c, ALLOC_FASTPATH);
> 1646            } while (cmpxchg_local(&c->freelist, object, object[c->offset])
> 1647
>  != object);
> 1648    #else
> 1649            unsigned long flags;
> 1650
>
> That code is part for SLUB_FASTPATH.
>
> I'm willing to test the patch, but don't know how fast I can find the
> time to do it, so my answer if your patch helps might be delayed until
> the weekend.

Mathieu, Christoph is on vacation and I'm not at all that familiar
with this cmpxchg_local() optimization, so if you could take a peek at
this bug report to see if you can spot something obviously wrong with
it, I would much appreciate that.
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