RE: [RFC][PATCH v4 -next 1/4] Move kmsg_dump(KMSG_DUMP_PANIC) belowsmp_send_stop()

[Luck, Tony]

> What if we send the REBOOT_IPI first and let it block for up to a second.
> Most code paths that are done with spin_locks will use
> spin_lock_irqrestore.  As soon as the interrupts are re-enabled the
> REBOOT_IPI comes in and takes the processor.  If after a second the cpu
> still is blocking interrupts, just use the NMI as a big hammer to shut it
> down.

This looks good - it certainly deals with my "if we just let them run
a bit, they'd release the locks" quibble.  One second sounds very
generous - but I'm not going to bikeshed that (so long as it is a total
of one second - not one second per cpu). So the pseudo-code is:

	send_reboot_ipi_to_everyone_else()

	wait_1_second()

	for_each_cpu_that_didnt_respond_to_reboot_ipi {
		hit_that_cpu_with_NMI()
	}

Perhaps a notification printk() if we had to use the NMI hammer?

-Tony
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