linux-kernel - [PATCH] sched_ext: Fix NULL pointer dereferences in put_prev_task

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Message-ID: <dc2d908cd429473a9d46255272231f38@honor.com>
Date: Mon, 9 Jun 2025 11:36:15 +0000
From: liuwenfang <liuwenfang@...or.com>
To: 'Tejun Heo' <tj@...nel.org>
CC: 'David Vernet' <void@...ifault.com>, 'Andrea Righi' <arighi@...dia.com>,
	'Changwoo Min' <changwoo@...lia.com>, 'Ingo Molnar' <mingo@...hat.com>,
	'Peter Zijlstra' <peterz@...radead.org>, 'Juri Lelli'
	<juri.lelli@...hat.com>, 'Vincent Guittot' <vincent.guittot@...aro.org>,
	'Dietmar Eggemann' <dietmar.eggemann@....com>, 'Steven Rostedt'
	<rostedt@...dmis.org>, 'Ben Segall' <bsegall@...gle.com>, 'Mel Gorman'
	<mgorman@...e.de>, 'Valentin Schneider' <vschneid@...hat.com>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>
Subject: [PATCH] sched_ext: Fix NULL pointer dereferences in put_prev_task_scx

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@...onor.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