- get rid of rq->frozen, fix context switch races.

kernel/sched.c

@@ -135,7 +135,6 @@ struct prio_array {
  */
 struct runqueue {
 	spinlock_t lock;
-	spinlock_t frozen;
 	unsigned long nr_running, nr_switches, expired_timestamp;
 	signed long nr_uninterruptible;
 	task_t *curr, *idle;
@@ -403,7 +402,7 @@ void sched_exit(task_t * p)
 #if CONFIG_SMP || CONFIG_PREEMPT
 asmlinkage void schedule_tail(void)
 {
-	spin_unlock_irq(&this_rq()->frozen);
+	spin_unlock_irq(&this_rq()->lock);
 }
 #endif
 
@@ -828,9 +827,6 @@ asmlinkage void schedule(void)
 	if (likely(prev != next)) {
 		rq->nr_switches++;
 		rq->curr = next;
-		spin_lock(&rq->frozen);
-		spin_unlock(&rq->lock);
-
 		context_switch(prev, next);
 
 		/*
@@ -840,10 +836,8 @@ asmlinkage void schedule(void)
 		 */
 		mb();
 		rq = this_rq();
-		spin_unlock_irq(&rq->frozen);
-	} else {
-		spin_unlock_irq(&rq->lock);
 	}
+	spin_unlock_irq(&rq->lock);
 
 	reacquire_kernel_lock(current);
 	preempt_enable_no_resched();
@@ -1599,7 +1593,6 @@ void __init sched_init(void)
 		rq->active = rq->arrays;
 		rq->expired = rq->arrays + 1;
 		spin_lock_init(&rq->lock);
-		spin_lock_init(&rq->frozen);
 		INIT_LIST_HEAD(&rq->migration_queue);
 
 		for (j = 0; j < 2; j++) {