Messages in this thread | | | Date | Fri, 30 Jun 2017 21:21:23 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH RFC 02/26] task_work: Replace spin_unlock_wait() with lock/unlock pair |
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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 ;)
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.
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.
Oleg.
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