linux-kernel - [PATCH] sched: pick_next_rt_entity(): checked list

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Message-Id: <20230128-list-entry-null-check-sched-v1-1-c93085ee0055@diag.uniroma1.it>
Date:   Sat, 28 Jan 2023 16:26:15 +0000
From:   Pietro Borrello <borrello@...g.uniroma1.it>
To:     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>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Dmitry Adamushko <dmitry.adamushko@...il.com>
Cc:     Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>, Jakob Koschel <jkl820.git@...il.com>,
        Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
        Pietro Borrello <borrello@...g.uniroma1.it>
Subject: [PATCH] sched: pick_next_rt_entity(): checked list_entry

Commit 326587b84078 ("sched: fix goto retry in pick_next_task_rt()")
removed any path which could make pick_next_rt_entity() return NULL.
However, BUG_ON(!rt_se) in _pick_next_task_rt() (the only caller of
pick_next_rt_entity()) still checks the error condition, which can
never happen, since list_entry() never returns NULL. Return
list_first_entry_or_null(queue, ...) to allow BUG to check the only
possible error condition here: the queue being empty which should
never happen.

Fixes: 326587b84078 ("sched: fix goto retry in pick_next_task_rt()")
Signed-off-by: Pietro Borrello <borrello@...g.uniroma1.it>
---
 kernel/sched/rt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index ed2a47e4ddae..6088d5d83b75 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1777,7 +1777,7 @@ static struct sched_rt_entity *pick_next_rt_entity(struct rt_rq *rt_rq)
 	BUG_ON(idx >= MAX_RT_PRIO);
 
 	queue = array->queue + idx;
-	next = list_entry(queue->next, struct sched_rt_entity, run_list);
+	next = list_first_entry_or_null(queue, struct sched_rt_entity, run_list);
 
 	return next;
 }

---
base-commit: 2241ab53cbb5cdb08a6b2d4688feb13971058f65
change-id: 20230128-list-entry-null-check-sched-a3f3dfd6d468

Best regards,
-- 
Pietro Borrello <borrello@...g.uniroma1.it>