On Fri, Aug 11, 2017 at 11:06:01AM +0200, Peter Zijlstra wrote: > On Thu, Aug 10, 2017 at 02:18:30PM -0400, Waiman Long wrote: > > On 08/10/2017 12:22 PM, Waiman Long wrote: > > > On 08/10/2017 12:15 PM, Peter Zijlstra wrote: > > > >> Might as well do an explicit: > > >> > > >> smp_mb__before_atomic() > > >> cmpxchg_relaxed() > > >> smp_mb__after_atomic() > > >> > > >> I suppose and not introduce new primitives. > > > > I think we don't need smp_mb__after_atomic(). The read has to be fully > > ordered, but the write part may not need it as the control dependency of > > the old value should guard against incorrect action. Right? > > You'd think that, but IIRC there was something funny about using the SC > return flag for control dependencies. Will?
Yeah, that's right, you can't use the STXR status flag to create control dependencies. Will
