stop_machine: convert cpu notifier to return encapsulate errno value

In commit e6bde73b ("cpu-hotplug: return
better errno on cpu hotplug failure"), the cpu notifier can return an
encapsulated errno value.

This converts the cpu notifier to return an encapsulated errno value for
stop_machine().
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/stop_machine.c

@@ -304,7 +304,7 @@ static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
 		p = kthread_create(cpu_stopper_thread, stopper, "migration/%d",
 				   cpu);
 		if (IS_ERR(p))
-			return NOTIFY_BAD;
+			return notifier_from_errno(PTR_ERR(p));
 		get_task_struct(p);
 		kthread_bind(p, cpu);
 		sched_set_stop_task(cpu, p);
@@ -372,7 +372,7 @@ static int __init cpu_stop_init(void)
 	/* start one for the boot cpu */
 	err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,
 				    bcpu);
-	BUG_ON(err == NOTIFY_BAD);
+	BUG_ON(err != NOTIFY_OK);
 	cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
 	register_cpu_notifier(&cpu_stop_cpu_notifier);