On Mon, 2014-02-10 at 20:58 +0100, Peter Zijlstra wrote:
> +unqueue:
> + /*
> + * Step - A -- stabilize @prev
> + *
> + * Undo our @prev->next assignment; this will make @prev's
> + * unlock()/unqueue() wait for a next pointer since @lock points to us
> + * (or later).
> + */
> +
> + for (;;) {
> + if (prev->next == node &&
> + cmpxchg(&prev->next, node, NULL) == node)
> + break;
> +
> + /*
> + * We can only fail the cmpxchg() racing against an unlock(),
> + * in which case we should observe @node->locked becomming
> + * true.
> + */
> + if (smp_load_acquire(&node->locked))
> + return true;
> +
> + /*
> + * Or we race against a concurrent unqueue()'s step-B, in which
> + * case its step-C will write us a new @node->prev pointer.
> + */
> + prev = ACCESS_ONCE(node->prev);
Should we also add an arch_mutex_cpu_relax() to this loop?
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