linux-kernel - Re: [GIT PULL] SLAB changes for v2.6.39-rc1

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Date:	Sun, 27 Mar 2011 11:59:33 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Pekka Enberg <penberg@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	Eric Dumazet <eric.dumazet@...il.com>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	tj@...nel.org, npiggin@...nel.dk, rientjes@...gle.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [GIT PULL] SLAB changes for v2.6.39-rc1

On 03/24/2011 09:51 PM, Christoph Lameter wrote:
> On Thu, 24 Mar 2011, Pekka Enberg wrote:
>
> >  Thanks, Ingo! Christoph, may I have your sign-off for the patch and
> >  I'll send it to Linus?
>
>
> Subject: SLUB: Write to per cpu data when allocating it
>
> It turns out that the cmpxchg16b emulation has to access vmalloced
> percpu memory with interrupts disabled. If the memory has never
> been touched before then the fault necessary to establish the
> mapping will not to occur and the kernel will fail on boot.
>

I don't get it.  Disabling interrupts doesn't disable faults.

> Fix that by reusing the CONFIG_PREEMPT code that writes the
> cpu number into a field on every cpu. Writing to the per cpu
> area before causes the mapping to be established before we get
> to a cmpxchg16b emulation.
>
> Tested-by: Ingo Molnar<mingo@...e.hu>
> Signed-off-by: Christoph Lameter<cl@...ux.com>
>
> ---
>   mm/slub.c |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c	2011-03-24 14:03:10.000000000 -0500
> +++ linux-2.6/mm/slub.c	2011-03-24 14:04:08.000000000 -0500
> @@ -1604,7 +1604,7 @@ static inline void note_cmpxchg_failure(
>
>   void init_kmem_cache_cpus(struct kmem_cache *s)
>   {
> -#if defined(CONFIG_CMPXCHG_LOCAL)&&  defined(CONFIG_PREEMPT)
> +#ifdef CONFIG_CMPXCHG_LOCAL
>   	int cpu;
>
>   	for_each_possible_cpu(cpu)
> --
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-- 
error compiling committee.c: too many arguments to function

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