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Date: Tue, 9 Mar 2010 12:22:53 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
       Pekka Enberg <penberg@cs.helsinki.fi>,
       Christoph Lameter <cl@linux-foundation.org>
Subject: Re: mm: Do not iterate over NR_CPUS in __zone_pcp_update()
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On Mon, 8 Mar 2010 10:21:04 +0100 (CET)
Thomas Gleixner <tglx@linutronix.de> wrote:

> __zone_pcp_update() iterates over NR_CPUS instead of limiting the
> access to the possible cpus. This might result in access to
> uninitialized areas as the per cpu allocator only populates the per
> cpu memory for possible cpus.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  mm/page_alloc.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6/mm/page_alloc.c
> ===================================================================
> --- linux-2.6.orig/mm/page_alloc.c
> +++ linux-2.6/mm/page_alloc.c
> @@ -3224,7 +3224,7 @@ static int __zone_pcp_update(void *data)
>  	int cpu;
>  	unsigned long batch = zone_batchsize(zone), flags;
>  
> -	for (cpu = 0; cpu < NR_CPUS; cpu++) {
> +	for_each_possible_cpu(cpu) {
>  		struct per_cpu_pageset *pset;
>  		struct per_cpu_pages *pcp;
>  

I'm having trouble working out whether we want to backport this into
2.6.33.x or earlier.  Help?