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Date: Thu, 20 Dec 2012 17:36:11 +0000
From: Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH] kexec: disable non-boot CPUs
Message-ID: <20121220173611.GC5387@mudshark.cambridge.arm.com>
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To: Stephen Warren <swarren@wwwdotorg.org>
Cc: "linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>, "kexec@lists.infradead.org" <kexec@lists.infradead.org>, Stephen Warren <swarren@nvidia.com>, Eric Biederman <ebiederm@xmission.com>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>

On Thu, Dec 20, 2012 at 05:21:56PM +0000, Stephen Warren wrote:
> On 12/20/2012 03:49 AM, Will Deacon wrote:
> > If you do manage to get this merged, please can you follow up with a patch
> > to remove the smp_kill_cpus bits from arch/arm/kernel/smp.c please? It only
> > exists as a hook to do exactly this and currently nobody is using it afaict.
> 
> I originally implemented this in
> arch/arm/kernel/process.c:machine_shutdown(), which currently is:
> 
> void machine_shutdown(void)
> {
> #ifdef CONFIG_SMP
> 	smp_send_stop();
> #endif
> }
> 
> and I changed it to something like:
> 
> void machine_shutdown(void)
> {
> #ifdef CONFIG_HOTPLUG_CPU
>  	disable_nonboot_cpus();
> #elifdef CONFIG_SMP
> 	smp_send_stop();
> #endif
> }
> 
> ... but then figured that moving it up into the core kexec code would be
> better, so that everything always worked the same way.

Hmmm, isn't this racy: requiring the secondaries to hit idle and notice
they're offline and call cpu_die before the primary has replace the kernel
image?

> Anyway, the change above addresses Eric's concern about isolating the
> change to ARM. Does that seem like a reasonable thing for the ARM code
> to do?

I think you're better off using what we currently have and hanging your code
off platform_cpu_kill.

Will

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