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* Before starting to take locks, do a quick, unlocked test to see whether
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529
* it's possible that this load could migrate backwards and occur before
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* we actually enter this function, so we might miss a sinval message that
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532
* backwards over a preceding lock acquisition, so it should be OK. If we
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* haven't acquired a lock preventing against further relevant
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* invalidations, any such occurrence is not much different than if the