[PATCH] sched_ext: Fix NULL pointer dereferences in put_prev_task_scx

[liuwenfang <liuwenfang@honor.com>]

As put_prev_task can be used in other kernel modules which can lead
to a NULL pointer. Fix this by checking for a valid next.

Signed-off-by: l00013971 <l00013971@hihonor.com>
---
 kernel/sched/ext.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index f5133249f..6a579babd 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3262,7 +3262,7 @@ static void put_prev_task_scx(struct rq *rq, struct task_struct *p,
 		 * ops.enqueue() that @p is the only one available for this cpu,
 		 * which should trigger an explicit follow-up scheduling event.
 		 */
-		if (sched_class_above(&ext_sched_class, next->sched_class)) {
+		if (next && sched_class_above(&ext_sched_class, next->sched_class)) {
 			WARN_ON_ONCE(!static_branch_unlikely(&scx_ops_enq_last));
 			do_enqueue_task(rq, p, SCX_ENQ_LAST, -1);
 		} else {
-- 
2.17.1