On Tue, Nov 11, 2008 at 06:20:50PM +0100, Oleg Nesterov wrote: > On 11/11, Dmitry Torokhov wrote: > > > > On Fri, Nov 07, 2008 at 04:43:25PM +0100, Oleg Nesterov wrote: > > > > > > While we are here, what is the reason for atkbd_schedule_event_work()->wmb() ? > > > It looks absolutely bogus. Is it for atkbd_event_work() ? In that case it > > > is not needed, it must see all previous STOREs because both queue_work() and > > > run_workqueue() take cwq->lock. And in any case, > > > test_and_set_bit(WORK_STRUCT_PENDING) implies mb(). > > > > I wanted to be sure that event_mask is set before we schedule event_work > > and I don't want to rely on details of queue_delayed_work > > implementation. If the fact that queue_delayed_work acts as a barrier > > would be listed part of its published spec I would gladly remove wmb() > > from atkbd. > > Yes, queue_delayed_work() acts as a barrier for the work->func(), otherwise > almost any code which uses wqs is broken. > > But let me repeat, if queue_delayed_work() fails becuase this work is > already queued we (in this particular case) need mb(), not wmb(). Or > atkbd_schedule_event_work() can miss a bit in ->event_mask. So I think > this wmb() is misleading. Could you please explain why wmb() is not enough and full mb() is needed in this case? I thought that if write happens before we decide whether to schedule event_work or not it would be enough. > And unneeded because queue_work() implies mb(), > but this is not really documented. > It would be great if we can get it documented and then i'd drop *mb() from atkbd. Thanks. -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
