On 03/15, Paul E. McKenney wrote: > > On Fri, Mar 15, 2013 at 07:34:32PM +0100, Frederic Weisbecker wrote: > > 2013/3/15 Oleg Nesterov <o...@redhat.com>: > > > > > > My point was: should we fix atomic_add_unless() then? If not, why > > > should atomic_add_unless_negative() differ? > > > > They shouldn't differ I guess. > > Completely agreed. It is not like memory ordering is simple, so we should > keep the rules simple.
It is hardly possible to argue with this ;) > The rule is that if an atomic primitive returns non-void, then there is > a full memory barrier before and after. This case is documented... > This applies to primitives > returning boolean as well, with atomic_dec_and_test() setting this > precedent from what I can see. I don't think this is the "fair" comparison. Unlike atomic_add_unless(), atomic_dec_and_test() always changes the memory even if it "fails". If atomic_add_unless() returns 0, nothing was changed and if we add the barrier it is not clear what it should be paired with. But OK. I have to agree that "keep the rules simple" makes sense, so we should change atomic_add_unless() as well. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/