linux-kernel - Re: [PATCH] x86: fix system without memory on node0

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Date:	Wed, 13 May 2009 15:35:04 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Jack Steiner <steiner@....com>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Mike Travis <travis@....com>
Subject: Re: [PATCH] x86: fix system without memory on node0


* Yinghai Lu <yinghai@...nel.org> wrote:

> Jack found that crash with doesn't have memory on node0.
> 
> it turns out with per_cpu changeset, node_number for BSP will be 
> alway 0, and it is consistent to cpu_to_node() that is to near 
> node already. aka when numa_set_node() for node0 is called early 
> before per_cpu area is setup
> 
> try to set the node_number for boot cpu, after we get per_cpu area 
> setup.
> 
> [ Impact: fix crashing on memoryless node 0]
> 
> Reported-by: Jack Steiner <steiner@....com>
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> 
> ---
>  arch/x86/kernel/setup_percpu.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> Index: linux-2.6/arch/x86/kernel/setup_percpu.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/setup_percpu.c
> +++ linux-2.6/arch/x86/kernel/setup_percpu.c
> @@ -423,6 +423,14 @@ void __init setup_per_cpu_areas(void)
>  	early_per_cpu_ptr(x86_cpu_to_node_map) = NULL;
>  #endif
>  
> +#if defined(CONFIG_X86_64) && defined(CONFIG_NUMA)
> +	/*
> +	 * make sure boot cpu node_number is right, when boot cpu is on the
> +	 * node that doesn't have mem installed
> +	 */
> +	per_cpu(node_number, boot_cpu_id) = cpu_to_node(boot_cpu_id);
> +#endif

ok, that's a nice fix i guess.

Wouldnt it also be necessary/good to unify this code between 32-bit 
and 64-bit? 32-bit has cpu_to_node_map[], while 64-bit has percpu 
variables for that.

	Ingo
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