On 02/28, Peter Zijlstra wrote: > > On Sat, Feb 28, 2015 at 09:36:15PM +0100, Manfred Spraul wrote: > > +/* > > + * Place this after a control barrier (such as e.g. a spin_unlock_wait()) > > + * to ensure that reads cannot be moved ahead of the control_barrier. > > + * Writes do not need a barrier, they are not speculated and thus cannot > > + * pass the control barrier. > > + */ > > +#ifndef smp_mb__after_control_barrier > > +#define smp_mb__after_control_barrier() smp_rmb() > > +#endif > > Sorry to go bike shedding again; but should we call this: > > smp_acquire__after_control_barrier() ? > > The thing is; its not a full MB because: > > - stores might actually creep into it; while the control dependency > guarantees stores will not creep out, nothing is stopping them from > getting in; > > - its not transitive, and our MB is defined to be so. I agree, so perhaps it should be named smp_acquire_after_unlock_wait ? even if it is actually stronger than "acquire"... To me "control_barrier" looks a bit confusing. I think this helper should be only used after spin_unlock_wait() or spin_is_locked/unlocked(). In this case it is clear that this "barrier" pairs with release semantics of spin_unlock(). And we use it because we want to serialize with that unlock, as if we are taking this lock. But I won't insist. Oleg. -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html