On Thu, Jul 05, 2018 at 08:44:39AM -0700, Daniel Lustig wrote: > On 7/5/2018 8:31 AM, Paul E. McKenney wrote: > > On Thu, Jul 05, 2018 at 10:21:36AM -0400, Alan Stern wrote: > >> At any rate, it looks like instead of strengthening the relation, I > >> should write a patch that removes it entirely. I also will add new, > >> stronger relations for use with locking, essentially making spin_lock > >> and spin_unlock be RCsc. > > > > Only in the presence of smp_mb__after_unlock_lock() or > > smp_mb__after_spinlock(), correct? Or am I confused about RCsc? > > > > Thanx, Paul > > > > In terms of naming...is what you're asking for really RCsc? To me, > that would imply that even stores in the first critical section would > need to be ordered before loads in the second critical section. > Meaning that even x86 would need an mfence in either lock() or unlock()?
I think a LOCK operation always implies an atomic RmW, which will give full ordering guarantees on x86. I know there have been interesting issues involving I/O accesses in the past, but I think that's still out of scope for the memory model. Peter will know. Will
