[PATCH] fix for stuck cpus at boot]

From: Anton Blanchard <anton@samba.org>

From: Rusty Russell <rusty@rustcorp.com.au>

When hotplug cpu isn't enabled, cpu_is_offline is always false.  I had a stuck
cpu at boot that resulted in a lockup because we tried to start a migration
thread on it.  Instead of cpu_is_offline we can use !cpu_online which should
cover both the hotplug cpu enabled and disabled cases.

kernel/sched.c

@@ -3636,7 +3636,7 @@ void cpu_attach_domain(struct sched_domain *sd, int cpu)
 
 	spin_lock_irqsave(&rq->lock, flags);
 
-	if (cpu == smp_processor_id() || cpu_is_offline(cpu)) {
+	if (cpu == smp_processor_id() || !cpu_online(cpu)) {
 		rq->sd = sd;
 	} else {
 		init_completion(&req.done);