> spin_lock() must be a full memory barrier, we could relax the rules for
> spin_unlock _only_ because read reordering of the x86 is asymetric.
no, spin_lock() must guarantee that instructions within the critical
section only execute at one CPU at once. Ie. all effects of the critical
section are either fully visible to another critical section, or not
visible at all - this is guaranteed by Processor Ordering and the spinlock
variant. _How_ this all happens, what is executed and where and in what
order is completely irrelevant.
yes, it's more vulnerable to processor/chipset bugs. (I'd still like to
see your testcase folded into C and causal.c so that we can make more
formal validation.)
-- mingo
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