This function (stop_this_cpu) in
/arch/mips/kernel/smp.c does a local_irq_enable() and the adjacent comment says
that it’s because it may need to service _machine_restart IPI. Unfortunately,
smp_call_function only sends IPIs to cores that are still online ( it uses the
cpu_online_map U all_but_myself_map in smp_call_function_map()).
So the bottom-line is, should we still keep the local irqs
enabled or is this code totally redundant? I have seen other similar functions
in other archs where they actually disable the local irqs.