linux-kernel - [PATCH] sched: hoist ASSERT_EXCLUSIVE_WRITER(p->on_rq) above WRITE

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Message-ID: <20241114165352.1824956-1-jon@nutanix.com>
Date: Thu, 14 Nov 2024 09:53:52 -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: Jon Kohler <jon@...anix.com>
Subject: [PATCH] sched: hoist ASSERT_EXCLUSIVE_WRITER(p->on_rq) above WRITE_ONCE

In {activate|deactivate}_task(), hoist ASSERT_EXCLUSIVE_WRITER() to be
above WRITE_ONCE(p->on_rq), which matches the ordering listed in the
KCSAN documentation, kcsan-checks.h code comments, and the usage
pattern we already have in __block_task().

Signed-off-by: Jon Kohler <jon@...anix.com>
---
 kernel/sched/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a1c353a62c56..80a04c36b495 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2066,16 +2066,16 @@ void activate_task(struct rq *rq, struct task_struct *p, int flags)
 
 	enqueue_task(rq, p, flags);
 
-	WRITE_ONCE(p->on_rq, TASK_ON_RQ_QUEUED);
 	ASSERT_EXCLUSIVE_WRITER(p->on_rq);
+	WRITE_ONCE(p->on_rq, TASK_ON_RQ_QUEUED);
 }
 
 void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
 {
 	SCHED_WARN_ON(flags & DEQUEUE_SLEEP);
 
-	WRITE_ONCE(p->on_rq, TASK_ON_RQ_MIGRATING);
 	ASSERT_EXCLUSIVE_WRITER(p->on_rq);
+	WRITE_ONCE(p->on_rq, TASK_ON_RQ_MIGRATING);
 
 	/*
 	 * Code explicitly relies on TASK_ON_RQ_MIGRATING begin set *before*
-- 
2.43.0