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Re: [Xen-devel] [PATCH v5 1/8] qspinlock: Introducing a 4-byte queue spinlock implementation



Forgot to ask...

On 02/26, Waiman Long wrote:
>
> +notify_next:
> +     /*
> +      * Wait, if needed, until the next one in queue set up the next field
> +      */
> +     while (!(next = ACCESS_ONCE(node->next)))
> +             arch_mutex_cpu_relax();
> +     /*
> +      * The next one in queue is now at the head
> +      */
> +     smp_store_release(&next->wait, false);

Do we really need smp_store_release()? It seems that we can rely on the
control dependency here. And afaics there is no need to serialise this
store with other changes in *lock, plus they all have mb's anyway.

Oleg.


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