[RESEND PATCH] ARM: kexec: Fix validating CPU hotplug support

Russell King - ARM Linux linux at arm.linux.org.uk
Tue Nov 4 02:55:25 PST 2014

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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according to speedtest.net.

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