On Wed, Jan 27, 2016 at 06:22:04PM +0000, Will Deacon wrote: > As much as we'd like to live in a world where RELEASE -> ACQUIRE is > always cheaply ordered and can be used to construct UNLOCK -> LOCK > definitions with similar guarantees, the grim reality is that this isn't > even possible on x86 (thanks to Paul for bringing us crashing down to > Earth). > > This patch handles the issue by introducing a new barrier macro, > smp_mb__after_release_acquire, that can be placed after an ACQUIRE that > either reads from a RELEASE or is in program-order after a RELEASE. The > barrier upgrades the RELEASE-ACQUIRE pair to a full memory barrier, > implying global transitivity. At the moment, it doesn't have any users, > so its existence serves mainly as a documentation aid and a potential > stepping stone to the reintroduction of smp_mb__after_unlock_lock() used > by RCU. > > Documentation/memory-barriers.txt is updated to describe more clearly > the ACQUIRE and RELEASE ordering in this area and to show some examples > of the new barrier in action. So the obvious question is: do we have a use-case? -- 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
