Re: [PATCH v3 4/4] futex: Avoid taking hb lock if nothing to wakeup

[Davidlohr Bueso]

On Fri, 2013-12-20 at 11:54 -0800, Linus Torvalds wrote:
> On Fri, Dec 20, 2013 at 11:30 AM, Davidlohr Bueso <davidlohr@xxxxxx> wrote:
> >
> > So we'd need the barrier right after the ticket increment (ie: the xadd
> > TICKET_LOCK_INC in x86), and cannot rely on the barrier after the lock
> > is taken as we could miss waiters that are just spinning trying to take
> > it. Is this implicitly guaranteed across all archs?
> 
> Not necessarily. But I don't see why threads spinning on it would be
> special? If you spin on things, you've already updated the head
> counter, so even spinners *are* visible, even if they haven't actually
> gotten the lock yet.

Fair enough, just making sure we're covering all cases.

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