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

On 03/02/2014 08:31 AM, Oleg Nesterov wrote:
Forgot to ask...

On 02/26, Waiman Long wrote:
+       /*
+        * 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.


I am just following the current logic in the mcs_spin_unlock function. It is probably true that we don't need the release semantic in this particular case.


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