sched_ext: Open-code task_linked_on_dsq()

task_linked_on_dsq() exists as a helper because it used to test both the
rbtree and list nodes. It now only tests the list node and the list node
will soon be used for something else too. The helper doesn't improve
anything materially and the naming will become confusing. Open-code the list
node testing and remove task_linked_on_dsq()
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>

kernel/sched/ext.c

@@ -1572,18 +1572,13 @@ static void task_unlink_from_dsq(struct task_struct *p,
 	list_del_init(&p->scx.dsq_list.node);
 }
 
-static bool task_linked_on_dsq(struct task_struct *p)
-{
-	return !list_empty(&p->scx.dsq_list.node);
-}
-
 static void dispatch_dequeue(struct rq *rq, struct task_struct *p)
 {
 	struct scx_dispatch_q *dsq = p->scx.dsq;
 	bool is_local = dsq == &rq->scx.local_dsq;
 
 	if (!dsq) {
-		WARN_ON_ONCE(task_linked_on_dsq(p));
+		WARN_ON_ONCE(!list_empty(&p->scx.dsq_list.node));
 		/*
 		 * When dispatching directly from the BPF scheduler to a local
 		 * DSQ, the task isn't associated with any DSQ but
@@ -1604,7 +1599,7 @@ static void dispatch_dequeue(struct rq *rq, struct task_struct *p)
 	*/
 	if (p->scx.holding_cpu < 0) {
 		/* @p must still be on @dsq, dequeue */
-		WARN_ON_ONCE(!task_linked_on_dsq(p));
+		WARN_ON_ONCE(list_empty(&p->scx.dsq_list.node));
 		task_unlink_from_dsq(p, dsq);
 		dsq_mod_nr(dsq, -1);
 	} else {
@@ -1614,7 +1609,7 @@ static void dispatch_dequeue(struct rq *rq, struct task_struct *p)
 		 * holding_cpu which tells dispatch_to_local_dsq() that it lost
 		 * the race.
 		 */
-		WARN_ON_ONCE(task_linked_on_dsq(p));
+		WARN_ON_ONCE(!list_empty(&p->scx.dsq_list.node));
 		p->scx.holding_cpu = -1;
 	}
 	p->scx.dsq = NULL;