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 14:36:24 -0800
From:	Zachary Amsden <zach@...are.com>
To:	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 14:06 -0800, Yinghai Lu wrote:

> >> 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.
> 
> 
> CPU hot plug path will call smp_prepare_boot_cpu?
> it is using __init instead of __cpuinit?

No, but moving the place where cpu is moved into online map might break
hotplug.  In any case, I don't see anything wrong with your change now
that I look closer.

Zach

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