On Mon, Jul 13, 2015 at 03:24:18PM +0100, Will Deacon wrote: > On Mon, Jul 13, 2015 at 02:09:50PM +0100, Peter Hurley wrote: > > On 07/13/2015 08:15 AM, Will Deacon wrote: > > > smp_mb__after_unlock_lock is used to promote an UNLOCK + LOCK sequence > > > into a full memory barrier. > > > > > > However: > > > > > > - This ordering guarantee is already provided without the barrier on > > > all architectures apart from PowerPC > > > > > > - The barrier only applies to UNLOCK + LOCK, not general > > > RELEASE + ACQUIRE operations > > > > I'm unclear what you mean here: do you mean > > A) a memory barrier is not required between RELEASE M + ACQUIRE N when you > > want to maintain distinct order between those operations on all arches > > (with the possible exception of PowerPC), or, > > B) no one is using smp_mb__after_unlock_lock() in that way right now. > > My understanding is (B), but Peter and I don't seem to agree yet! > I'll tighten up the text once we reach a conclusion. I'm fairly sure (but I've not looked) that nobody does in fact rely on this. So I'm in agreement with B, and I'm quibbling on what exactly A means ;-) -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
