[PATCH] Export cpu notifiers and do locking.

The registration and unregistration of CPU notifiers should be done
under the cpucontrol sem.  They should also be exported.

kernel/cpu.c

@@ -19,13 +19,23 @@ static struct notifier_block *cpu_chain;
 /* Need to know about CPUs going up/down? */
 int register_cpu_notifier(struct notifier_block *nb)
 {
-	return notifier_chain_register(&cpu_chain, nb);
+	int ret;
+
+	if ((ret = down_interruptible(&cpucontrol)) != 0)
+		return ret;
+	ret = notifier_chain_register(&cpu_chain, nb);
+	up(&cpucontrol);
+	return ret;
 }
+EXPORT_SYMBOL(register_cpu_notifier);
 
 void unregister_cpu_notifier(struct notifier_block *nb)
 {
-	notifier_chain_unregister(&cpu_chain,nb);
+	down(&cpucontrol);
+	notifier_chain_unregister(&cpu_chain, nb);
+	up(&cpucontrol);
 }
+EXPORT_SYMBOL(unregister_cpu_notifier);
 
 int __devinit cpu_up(unsigned int cpu)
 {