[PATCH] Hotplug CPUs: don't pull onto offline CPUs

Don't move tasks onto offline cpus in load_balance and wake_task (the
latter is caused by a completion run from stop_machine).

Note that cpu_is_offline() is a noop when CONFIG_HOTPLUG_CPU=n.

kernel/sched.c

@@ -666,8 +666,8 @@ static int try_to_wake_up(task_t * p, unsigned int state, int sync)
 			if (unlikely(sync && !task_running(rq, p) &&
 				(task_cpu(p) != smp_processor_id()) &&
 					cpu_isset(smp_processor_id(),
-							p->cpus_allowed))) {
-
+							p->cpus_allowed) &&
+					!cpu_is_offline(smp_processor_id()))) {
 				set_task_cpu(p, smp_processor_id());
 				task_rq_unlock(rq, &flags);
 				goto repeat_lock_task;
@@ -1299,6 +1299,9 @@ static void load_balance(runqueue_t *this_rq, int idle, cpumask_t cpumask)
 	struct list_head *head, *curr;
 	task_t *tmp;
 
+	if (cpu_is_offline(this_cpu))
+		goto out;
+
 	busiest = find_busiest_queue(this_rq, this_cpu, idle,
 				     &imbalance, cpumask);
 	if (!busiest)