Hi Tejun, On 03/26, Tejun Heo wrote: > > On Thu, Mar 22, 2018 at 12:24:12PM +0100, Oleg Nesterov wrote: > > > > But why flush_rcu_work() can't simply do flush_work() ? > > > > If WORK_STRUCT_PENDING_BIT was set by us (rcu_work_rcufn() succeeded) we do > > not > > need rcu_barrier(). Why should we care about other rcu callbacks? > > > > If rcu_work_rcufn() fails and someone else sets PENDING, how this > > rcu_barrier() > > can help? We didn't even do call_rcu() in this case. > > > > In short. Once flush_work() returns we know that rcu callback which queued > > this > > work is finished. It doesn't matter if it was fired by us or not. And if it > > was > > not fired by us, then rcu_barrier() doesn't imply a grace period anyway. > > flush_*work() guarantees to wait for the completion of the latest > instance of the work item which was visible to the caller. We can't > guarantee that w/o rcu_barrier().
And this is what I can't understand. So let me repeat. Could you please describe a use-case which needs flush_rcuwork() with rcu_barrier() ? > > And again, at least for fs/aio.c it doesn't offer too much but sub-optimal > > compared to call_rcu() + schedule_work() by hand. > > Sure, this isn't about performance. It's about making code less > painful on the eyes. If performance matters, we sure can hand-craft > things, which doesn't seem to be the case, right? OK, I won't insist. Oleg.
