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Date: Mon, 15 Feb 2010 17:15:35 +1100
From: Nick Piggin <npiggin@suse.de>
To: Andi Kleen <andi@firstfloor.org>
Cc: penberg@cs.helsinki.fi, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
       haicheng.li@intel.com, rientjes@google.com
Subject: Re: [PATCH] [4/4] SLAB: Fix node add timer race in cache_reap
Message-ID: <20100215061535.GI5723@laptop>
References: <20100211953.850854588@firstfloor.org>
 <20100211205404.085FEB1978@basil.firstfloor.org>
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On Thu, Feb 11, 2010 at 09:54:04PM +0100, Andi Kleen wrote:
> 
> cache_reap can run before the node is set up and then reference a NULL 
> l3 list. Check for this explicitely and just continue. The node
> will be eventually set up.

How, may I ask? cpuup_prepare in the hotplug notifier should always
run before start_cpu_timer.

> 
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
> 
> ---
>  mm/slab.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> Index: linux-2.6.32-memhotadd/mm/slab.c
> ===================================================================
> --- linux-2.6.32-memhotadd.orig/mm/slab.c
> +++ linux-2.6.32-memhotadd/mm/slab.c
> @@ -4093,6 +4093,9 @@ static void cache_reap(struct work_struc
>  		 * we can do some work if the lock was obtained.
>  		 */
>  		l3 = searchp->nodelists[node];
> +		/* Note node yet set up */
> +		if (!l3)
> +			break;
>  
>  		reap_alien(searchp, l3);
>  
> 
> --
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