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[...] > Using atomic_set_release() and atomic_read_acquire() on s->stage would > order the stamp allocations. Right. ww_acquire_init() takes the stamp with a relaxed increment, and nothing orders it before the relaxed store of stage 1: on a weakly-ordered CPU the younger thread can take the older stamp, wound the other one, and the test fails with -EDEADLK where nothing is wrong. x86 does not reorder them. v2 makes each stage store a release and the poll an acquire. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com