On Tue, 2013-11-19 at 11:13 -0800, Paul E. McKenney wrote:
> On Fri, Nov 08, 2013 at 11:52:05AM -0800, Tim Chen wrote:
> >
> > +/*
> > + * Releases the lock. The caller should pass in the corresponding node that
> > + * was used to acquire the lock.
> > + */
> > static void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
> > {
> > struct mcs_spinlock *next = ACCESS_ONCE(node->next);
> > @@ -51,7 +60,7 @@ static void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *nod
> > /*
> > * Release the lock by setting it to NULL
> > */
> > - if (cmpxchg(lock, node, NULL) == node)
> > + if (likely(cmpxchg(lock, node, NULL) == node))
>
> Agreed here as well. Takes a narrow race to hit this.
>
> So, did your testing exercise this path? If the answer is "yes",
Paul,
I did some instrumentation and confirmed that the path in question has
been exercised. So this patch should be okay.
Tim
> and if the issues that I called out in patch #1 are resolved:
>
> Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
>
> > return;
> > /* Wait until the next pointer is set */
> > while (!(next = ACCESS_ONCE(node->next)))
> >
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