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

[Linus Torvalds]

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.

                 Linus
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