Probably we should put question in another fashion, ie in the fasion of
overall design -- who should be
responsible for handling external nmis, 1) the cpu which apic is configured
to observe such nmis or 2) any cpu?
If we take 1) then no lock is needed and underlied code will report real cpu
number who observed nmi. If
we take 2) then lock is needed but we need a big comment in default_do_nmi
together with probably cpu number
fixed in serr\iochk printk's.
I am OK with both solutions.