diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 4043abe..55a4a50 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2449,10 +2449,11 @@ const struct sched_class rt_sched_class = {
  */
 static DEFINE_MUTEX(rt_constraints_mutex);
 
-/* Must be called with tasklist_lock held */
 static inline int tg_has_rt_tasks(struct task_group *tg)
 {
-	struct task_struct *g, *p;
+	struct task_struct *task;
+	struct css_task_iter it;
+	int ret = 0;
 
 	/*
 	 * Autogroups do not have RT tasks; see autogroup_create().
@@ -2460,12 +2461,12 @@ static inline int tg_has_rt_tasks(struct task_group *tg)
 	if (task_group_is_autogroup(tg))
 		return 0;
 
-	for_each_process_thread(g, p) {
-		if (rt_task(p) && task_group(p) == tg)
-			return 1;
-	}
+	css_task_iter_start(&tg->css, 0, &it);
+	while (!ret && (task = css_task_iter_next(&it)))
+		ret |= rt_task(task);
+	css_task_iter_end(&it);
 
-	return 0;
+	return ret;
 }
 
 struct rt_schedulable_data {
@@ -2496,9 +2497,10 @@ static int tg_rt_schedulable(struct task_group *tg, void *data)
 		return -EINVAL;
 
 	/*
-	 * Ensure we don't starve existing RT tasks.
+	 * Ensure we don't starve existing RT tasks if runtime turns zero.
 	 */
-	if (rt_bandwidth_enabled() && !runtime && tg_has_rt_tasks(tg))
+	if (rt_bandwidth_enabled() && !runtime &&
+	    tg->rt_bandwidth.rt_runtime && tg_has_rt_tasks(tg))
 		return -EBUSY;
 
 	total = to_ratio(period, runtime);
@@ -2564,7 +2566,6 @@ static int tg_set_rt_bandwidth(struct task_group *tg,
 		return -EINVAL;
 
 	mutex_lock(&rt_constraints_mutex);
-	read_lock(&tasklist_lock);
 	err = __rt_schedulable(tg, rt_period, rt_runtime);
 	if (err)
 		goto unlock;
@@ -2582,7 +2583,6 @@ static int tg_set_rt_bandwidth(struct task_group *tg,
 	}
 	raw_spin_unlock_irq(&tg->rt_bandwidth.rt_runtime_lock);
 unlock:
-	read_unlock(&tasklist_lock);
 	mutex_unlock(&rt_constraints_mutex);
 
 	return err;
@@ -2641,9 +2641,7 @@ static int sched_rt_global_constraints(void)
 	int ret = 0;
 
 	mutex_lock(&rt_constraints_mutex);
-	read_lock(&tasklist_lock);
 	ret = __rt_schedulable(NULL, 0, 0);
-	read_unlock(&tasklist_lock);
 	mutex_unlock(&rt_constraints_mutex);
 
 	return ret;