stop_machine: Kill cpu_stop_threads->setup() and cpu_stop_unpark()

Now that we always use stop_machine_unpark() to wake the stopper
threas up, we can kill ->setup() and fold cpu_stop_unpark() into
stop_machine_unpark().

And we do not need stopper->lock to set stopper->enabled = true.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: heiko.carstens@de.ibm.com
Link: http://lkml.kernel.org/r/20151009160051.GA10169@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/stop_machine.c

@@ -504,20 +504,11 @@ static void cpu_stop_park(unsigned int cpu)
 	WARN_ON(!list_empty(&stopper->works));
 }
 
-static void cpu_stop_unpark(unsigned int cpu)
-{
-	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
-
-	spin_lock_irq(&stopper->lock);
-	stopper->enabled = true;
-	spin_unlock_irq(&stopper->lock);
-}
-
 void stop_machine_unpark(int cpu)
 {
 	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 
-	cpu_stop_unpark(cpu);
+	stopper->enabled = true;
 	kthread_unpark(stopper->thread);
 }
 
@@ -527,7 +518,6 @@ static struct smp_hotplug_thread cpu_stop_threads = {
 	.thread_fn		= cpu_stopper_thread,
 	.thread_comm		= "migration/%u",
 	.create			= cpu_stop_create,
-	.setup			= cpu_stop_unpark,
 	.park			= cpu_stop_park,
 	.selfparking		= true,
 };