sched: Simplify yield_to()

Use guards to reduce gotos and simplify control flow.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/core.c

@@ -8888,55 +8888,46 @@ int __sched yield_to(struct task_struct *p, bool preempt)
 {
 	struct task_struct *curr = current;
 	struct rq *rq, *p_rq;
-	unsigned long flags;
 	int yielded = 0;
 
-	local_irq_save(flags);
-	rq = this_rq();
+	scoped_guard (irqsave) {
+		rq = this_rq();
 
 again:
-	p_rq = task_rq(p);
-	/*
-	 * If we're the only runnable task on the rq and target rq also
-	 * has only one task, there's absolutely no point in yielding.
-	 */
-	if (rq->nr_running == 1 && p_rq->nr_running == 1) {
-		yielded = -ESRCH;
-		goto out_irq;
-	}
+		p_rq = task_rq(p);
+		/*
+		 * If we're the only runnable task on the rq and target rq also
+		 * has only one task, there's absolutely no point in yielding.
+		 */
+		if (rq->nr_running == 1 && p_rq->nr_running == 1)
+			return -ESRCH;
 
-	double_rq_lock(rq, p_rq);
-	if (task_rq(p) != p_rq) {
-		double_rq_unlock(rq, p_rq);
-		goto again;
-	}
+		guard(double_rq_lock)(rq, p_rq);
+		if (task_rq(p) != p_rq)
+			goto again;
 
-	if (!curr->sched_class->yield_to_task)
-		goto out_unlock;
+		if (!curr->sched_class->yield_to_task)
+			return 0;
 
-	if (curr->sched_class != p->sched_class)
-		goto out_unlock;
+		if (curr->sched_class != p->sched_class)
+			return 0;
 
-	if (task_on_cpu(p_rq, p) || !task_is_running(p))
-		goto out_unlock;
+		if (task_on_cpu(p_rq, p) || !task_is_running(p))
+			return 0;
 
-	yielded = curr->sched_class->yield_to_task(rq, p);
-	if (yielded) {
-		schedstat_inc(rq->yld_count);
-		/*
-		 * Make p's CPU reschedule; pick_next_entity takes care of
-		 * fairness.
-		 */
-		if (preempt && rq != p_rq)
-			resched_curr(p_rq);
+		yielded = curr->sched_class->yield_to_task(rq, p);
+		if (yielded) {
+			schedstat_inc(rq->yld_count);
+			/*
+			 * Make p's CPU reschedule; pick_next_entity
+			 * takes care of fairness.
+			 */
+			if (preempt && rq != p_rq)
+				resched_curr(p_rq);
+		}
 	}
 
-out_unlock:
-	double_rq_unlock(rq, p_rq);
-out_irq:
-	local_irq_restore(flags);
-
-	if (yielded > 0)
+	if (yielded)
 		schedule();
 
 	return yielded;