See discussion here:

http://markmail.org/search/?q=concurrency-interest%20storestorefence%20#query:concurrency-interest%20storestorefence%20+page:1+mid:ui26jmrpjd32soxr+state:results

A storeStoreFence appears to be required in theory and perhaps on armv8 in practice, although no one has ever demonstrated such a race in the Real World.