diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index f4c2f8c..2cf06c2 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4125,26 +4125,24 @@ static void css_task_iter_advance_css_set(struct css_task_iter *it)
 
 static void css_task_iter_advance(struct css_task_iter *it)
 {
-	struct list_head *l = it->task_pos;
+	struct list_head *next;
 
 	lockdep_assert_held(&css_set_lock);
-	WARN_ON_ONCE(!l);
-
 repeat:
 	/*
 	 * Advance iterator to find next entry.  cset->tasks is consumed
 	 * first and then ->mg_tasks.  After ->mg_tasks, we move onto the
 	 * next cset.
 	 */
-	l = l->next;
+	next = it->task_pos->next;
 
-	if (l == it->tasks_head)
-		l = it->mg_tasks_head->next;
+	if (next == it->tasks_head)
+		next = it->mg_tasks_head->next;
 
-	if (l == it->mg_tasks_head)
+	if (next == it->mg_tasks_head)
 		css_task_iter_advance_css_set(it);
 	else
-		it->task_pos = l;
+		it->task_pos = next;
 
 	/* if PROCS, skip over tasks which aren't group leaders */
 	if ((it->flags & CSS_TASK_ITER_PROCS) && it->task_pos &&