On Tue, Nov 27, 2012 at 03:42:39PM -0800, Andrew Morton wrote:

quoted

+	/* Do not allow to execute any other task */
+	spin_lock_irqsave(&lock, flags);
+	while (1);

I suspect this doesn't do what you want it to do.

Firstly, please provide adequate code comments here so that code
readers do not also need to be mind readers.

If you want to stop this CPU dead in its tracks (why?) then

	local_irq_disable();
	while (1)
		;		/* Note correct code layout */

will do it.  But it means that the NMI watchdog (if present) will come
along and whack the machine in the head a few seconds later.  And this
does nothing to stop other CPUs.

But not being a mind reader, I'm really at a loss to suggest what
should be done here.  

It's hooking into the pm_power_off hook, which is called from kernel/sys.c
via arch code.  We will have already stopped all other CPUs at this point.

Why there's that while (1) there I don't know; when pm_power_off is not
hooked, we don't do anything like that - and what will happen in that
case is we'll return all the way back to sys_reboot(), which will call
do_exit(0) on us.

I don't see a problem with that, and I don't see why we need to spin
(without any power saving too) waiting for some event.  If we've called
sys_reboot with LINUX_REBOOT_CMD_POWER_OFF, we'd better have already
killed most of userspace off by that time anyway.