On 12/20/2012 03:49 AM, Will Deacon wrote:

Hi Stephen,

On Wed, Dec 19, 2012 at 11:44:41PM +0000, Stephen Warren wrote:

quoted

From: Stephen Warren <redacted>

Both the regular reboot and shutdown paths do this. It seems reasonable
for kexec to work the same way.

On the Tegra ARM SoC at least, this change allows kexec to work with SMP
enabled. ARM's machine_shutdown() simply puts all CPUs into a loop. If
the code of that loop is over-written, the CPUs may crash, and cause the
kexec'd kernel not to be able to initialize them. In practice, this
causes the kexec'd kernel to hang and/or crash. The intended way to
solve this is for ARM machines to provide a cpu_kill SMP operation to
e.g. power down the CPUs, or place them in reset. However, at least on
Tegra, the implementation of that function would simply be duplicating
the hotplug code that already exists, so it seems simpler to just call
disable_nonboot_cpus() for the kexec path, just like reboot/shutdown.

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.

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?