linux-kernel - Re: [RESEND PATCH] ARM: kexec: Fix validating CPU hotplug support

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Message-ID: <20141104105525.GE4042@n2100.arm.linux.org.uk>
Date:	Tue, 4 Nov 2014 10:55:25 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	HuKeping <hukeping@...wei.com>
Cc:	swarren@...dia.com, ebiederm@...ssion.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	sdu.liu@...wei.com, wangnan0@...wei.com, peifeiyue@...wei.com
Subject: Re: [RESEND PATCH] ARM: kexec: Fix validating CPU hotplug support

On Tue, Nov 04, 2014 at 05:40:25PM +0800, HuKeping wrote:
> Commit 2103f6cba61a8b8bea3fc1b63661d830a2125e76 added a hotplug checking in
> machine_kexec_prepare(), but it will lead a failure when loading the
> crash-kernel in some cases.
> 
> Kexec utility can load the crash kernel by two ways:
> 1. kexec -l kernel-image
> 2. kexec -p kernel-image
> 
> In case #1, for rapid reboot, it's correct to do the hotplug checking things,
> for it will shut down cpus in _cpu_down() later when command "kexec -e" be
> sent, this routine needs the support of cpu hotplug.
> 
> In case #2, for use on panic, it's unnecessary to do the same thing, the whole
> routing has no business with cpu shutting down. Check for cpu hot plug will
> lead a failure to load the kernel.

So what happens to the other CPUs when you kexec into the new kernel,
possibly overwriting the instructions which those CPUs are executing?

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