linux-kernel - [PATCH v2] sched: add READ_ONCE to task_on_rq

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Message-ID: <20241114210812.1836587-1-jon@nutanix.com>
Date: Thu, 14 Nov 2024 14:08:11 -0700
From: Jon Kohler <jon@...anix.com>
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>, Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org
Cc: Harshit Agarwal <harshit@...anix.com>, Phil Auld <pauld@...hat.com>,
        Jon Kohler <jon@...anix.com>
Subject: [PATCH v2] sched: add READ_ONCE to task_on_rq_queued

From: Harshit Agarwal <harshit@...anix.com>

task_on_rq_queued read p->on_rq without READ_ONCE, though p->on_rq is
set with WRITE_ONCE in {activate|deactivate}_task and smp_store_release
in __block_task, and also read with READ_ONCE in task_on_rq_migrating.

Make all of these accesses pair together by adding READ_ONCE in the
task_on_rq_queued.

Signed-off-by: Harshit Agarwal <harshit@...anix.com>
Reviewed-by: Phil Auld <pauld@...hat.com>
Cc: Jon Kohler <jon@...anix.com>
---
 kernel/sched/sched.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index c03b3d7b320e..dbbe5ce0dd96 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2277,7 +2277,7 @@ static inline int task_on_cpu(struct rq *rq, struct task_struct *p)
 
 static inline int task_on_rq_queued(struct task_struct *p)
 {
-	return p->on_rq == TASK_ON_RQ_QUEUED;
+	return READ_ONCE(p->on_rq) == TASK_ON_RQ_QUEUED;
 }
 
 static inline int task_on_rq_migrating(struct task_struct *p)
-- 
2.43.0