<rant>
Why do we even need a disable_nonboot_cpus in that path? machine_shutdown
on i386 and x86_64 should take care of that. Further the code that computes
the boot cpu is bogus (not all architectures require cpu == 0 to be
the boot cpu), and disabling non boot cpus appears to be a strong
x86ism, in the first place.
If the only reason for disable_nonboot_cpus there is to avoid the
WARN_ON in init_low_mappings() we should seriously consider killing
it. If we can wait for 2.6.22 the relocatable x86_64 patchset that
Andi has queued, has changes that kill the init_low_mapping() hack.
I'm not very comfortable with calling cpu_down in a common code path
right now either. I'm fairly certain we still don't have that
correct. So if we confine the mess that is cpu_down to #if
defined(CPU_HOTPLUG) && defined(CONFIG_EXPERIMENTAL) I don't care.
If we start using it everywhere I'm very nervous. I know the irq
migration when bringing a cpu down is strongly racy, and I don't think
we actually put cpus to sleep properly either.
</rant>
Eric
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