[PATCH 2/2] migration_call(CPU_DEAD): use spin_lock_irq() instead of task_rq_lock()

[Oleg Nesterov <oleg@tv-sign.ru>]

Change migration_call(CPU_DEAD) to use direct spin_lock_irq() instead of
task_rq_lock(rq->idle), rq->idle can't change its task_rq().

This makes the code a bit more symmetrical with migrate_dead_tasks()'s
path which uses spin_lock_irq/spin_unlock_irq.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- t/kernel/sched.c~2_RQ_LOCK	2007-08-24 20:31:03.000000000 +0400
+++ t/kernel/sched.c	2007-08-24 20:37:17.000000000 +0400
@@ -5381,13 +5381,13 @@ migration_call(struct notifier_block *nf
 		kthread_stop(rq->migration_thread);
 		rq->migration_thread = NULL;
 		/* Idle task back to normal (off runqueue, low prio) */
-		rq = task_rq_lock(rq->idle, &flags);
+		spin_lock_irq(&rq->lock);
 		deactivate_task(rq, rq->idle, 0);
 		rq->idle->static_prio = MAX_PRIO;
 		__setscheduler(rq, rq->idle, SCHED_NORMAL, 0);
 		rq->idle->sched_class = &idle_sched_class;
 		migrate_dead_tasks(cpu);
-		task_rq_unlock(rq, &flags);
+		spin_unlock_irq(&rq->lock);
 		migrate_nr_uninterruptible(rq);
 		BUG_ON(rq->nr_running != 0);