linux-kernel - Re: [PATCH] x86_64: not set boot cpu in cpu_online_map at smp_prepare_boot

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Date:	Mon, 26 Nov 2007 12:57:46 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Yinghai Lu <Yinghai.Lu@....COM>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86_64: not set boot cpu in cpu_online_map at
	smp_prepare_boot_cpu

On Mon, 2007-11-26 at 00:38 -0800, Yinghai Lu wrote:
> [PATCH] x86_64: not set boot cpu in cpu_online_map at smp_prepare_boot_cpu
> 
> in init/main.c boot_cpu_init() does that before
> 
> Signed-off-by: Yinghai Lu <yinghai.lu@....com>
> 
> diff --git a/arch/x86/kernel/smpboot_64.c b/arch/x86/kernel/smpboot_64.c
> index 500670c..966d124 100644
> --- a/arch/x86/kernel/smpboot_64.c
> +++ b/arch/x86/kernel/smpboot_64.c
> @@ -912,7 +912,7 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
>  void __init smp_prepare_boot_cpu(void)
>  {
>  	int me = smp_processor_id();
> -	cpu_set(me, cpu_online_map);
> +	/* already set me in cpu_online_map in boot_cpu_init() */
>  	cpu_set(me, cpu_callout_map);
>  	per_cpu(cpu_state, me) = CPU_ONLINE;
>  }


This ordering can be tricky wrt CPU hotplug.  Are you sure you are not
breaking CPU hotplug?  AFAIK, x86_64 has that right and the 32-bit code
had it wrong.

Zach

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