On Fri, Jun 30, 2017 at 09:21:23PM +0200, Oleg Nesterov wrote: > On 06/30, Paul E. McKenney wrote: > > > > On Fri, Jun 30, 2017 at 05:20:10PM +0200, Oleg Nesterov wrote: > > > > > > I do not think the overhead will be noticeable in this particular case. > > > > > > But I am not sure I understand why do we want to unlock_wait. Yes I agree, > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > > if it was not clear, I tried to say "why do we want to _remove_ unlock_wait". > > > > it has some problems, but still... > > > > > > The code above looks strange for me. If we are going to repeat this pattern > > > the perhaps we should add a helper for lock+unlock and name it unlock_wait2 ;) > > > > > > If not, we should probably change this code more: > > > > This looks -much- better than my patch! May I have your Signed-off-by? > > Only if you promise to replace all RCU flavors with a single simple implementation > based on rwlock ;) ;-) ;-) ;-) Here you go: https://github.com/pramalhe/ConcurrencyFreaks/blob/master/papers/poormanurcu-2015.pdf > Seriously, of course I won't argue, and it seems that nobody except me likes > this primitive, but to me spin_unlock_wait() looks like synchronize_rcu(() and > sometimes it makes sense. Well, that analogy was what led me to propose that its semantics be defined as spin_lock() immediately followed by spin_unlock(). But that didn't go over well. > Including this particular case. task_work_run() is going to flush/destroy the > ->task_works list, so it needs to wait until all currently executing "readers" > (task_work_cancel()'s which have started before ->task_works was updated) have > completed. Understood! Thanx, Paul
