I misread the algorithm, sorry. On second read, it appears to check out (modulo memory barriers!) up to the retry-on-fail, which, as Jacques Mattheij points ou

I misread the algorithm, sorry. On second read, it appears to check out (modulo memory barriers!) up to the retry-on-fail, which, as Jacques Mattheij points out elsewhere, leads to a failure in mutual exclusion. I've updated my reply to reflect this failure mode.