On Mon, Jul 13, 2015 at 03:09:15PM +0100, Will Deacon wrote: > On Mon, Jul 13, 2015 at 02:11:43PM +0100, Peter Zijlstra wrote: > > On Mon, Jul 13, 2015 at 01:15:04PM +0100, Will Deacon wrote: > > > smp_mb__after_unlock_lock is used to promote an UNLOCK + LOCK sequence > > > into a full memory barrier. > > > > > > However: > > > > > - The barrier only applies to UNLOCK + LOCK, not general > > > RELEASE + ACQUIRE operations > > > > No it does too; note that on ppc both acquire and release use lwsync and > > two lwsyncs do not make a sync. > > Really? IIUC, that means smp_mb__after_unlock_lock needs to be a full > barrier on all architectures implementing smp_store_release as smp_mb() + > STORE, otherwise the following isn't ordered: > > RELEASE X > smp_mb__after_unlock_lock() > ACQUIRE Y > > On 32-bit ARM (at least), the ACQUIRE can be observed before the RELEASE. I knew we'd had this conversation before ;) http://lkml.kernel.org/r/20150120093443.GA11596@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Will -- 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
