[PATCH v2] barriers: introduce smp_mb__release_acquire and update documentation

[Peter Zijlstra]

On Fri, Oct 09, 2015 at 10:40:39AM +0100, Will Deacon wrote:
> 
> >  - RELEASE -> ACQUIRE _chains_ (on shared variables) preserve causality,
> >    (because each link is fully ordered) but are not transitive.
> 
> Yup, and that's the same for UNLOCK -> LOCK, too.

Agreed, except RELEASE/ACQUIRE is more RCpc than UNLOCK/LOCK.

IFF we can get UNLOCK/LOCK as RCsc the chains are strongly transitive,
unlike the RELEASE/ACQUIRE chains, which will be weakly so.