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From:   Ze Gao <zegao2021@gmail.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Ben Segall <bsegall@google.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Mel Gorman <mgorman@suse.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Valentin Schneider <vschneid@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        linux-kernel@vger.kernel.org, Ze Gao <zegao@tencent.com>
Subject: [PATCH] sched_fork: Use READ_ONCE() for lockless read of current->normal_prio
Date:   Mon, 12 Jun 2023 11:35:05 +0800
Message-Id: <20230612033505.8148-1-zegao@tencent.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The current->normal_prio is locklessly accessed from sched_fork and
child's scheduler related initialization procedures heavily rely on
the value loaded. Thus we mark this load as READ_ONCE in case of
possible load tearing due to concurrent access from other paths, for
example if changes of parent's normal_prio happens to be requested
via some syscall.

Signed-off-by: Ze Gao <zegao@tencent.com>
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 944c3ae39861..37a13e4b734d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4699,7 +4699,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 	/*
 	 * Make sure we do not leak PI boosting priority to the child.
 	 */
-	p->prio = current->normal_prio;
+	p->prio = READ_ONCE(current->normal_prio);
 
 	uclamp_fork(p);
 
-- 
2.40.1