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Re: [Xen-devel] [PATCH 10/11] qspinlock: Paravirt support

Il 17/06/2014 00:08, Waiman Long ha scritto:
+void __pv_queue_unlock(struct qspinlock *lock)
+       int val = atomic_read(&lock->val);
+       native_queue_unlock(lock);
+       if (val & _Q_LOCKED_SLOW)
+               ___pv_kick_head(lock);

Again a race can happen here between the reading and writing of the lock
value. I can't think of a good way to do that without using cmpxchg.

Could you just use xchg on the locked byte?


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