netdev - [PATCH 2/3] net: sched: consistently use rcu_replace_pointer() in taprio

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Message-ID: <20240807103943.1633950-2-dmantipov@yandex.ru>
Date: Wed,  7 Aug 2024 13:39:42 +0300
From: Dmitry Antipov <dmantipov@...dex.ru>
To: Vinicius Costa Gomes <vinicius.gomes@...el.com>
Cc: Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org,
	lvc-project@...uxtesting.org,
	Dmitry Antipov <dmantipov@...dex.ru>
Subject: [PATCH 2/3] net: sched: consistently use rcu_replace_pointer() in taprio_change()

According to Vinicius (and carefully looking through the whole thing
once again), txtime branch of 'taprio_change()' is not going to race
against 'advance_sched()'. But using 'rcu_replace_pointer()' in the
former may be a good idea as well.

Suggested-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>
Signed-off-by: Dmitry Antipov <dmantipov@...dex.ru>
---
 net/sched/sch_taprio.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 59fad74d5ff9..9f4e004cdb8b 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -1952,7 +1952,9 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
 			goto unlock;
 		}
 
-		rcu_assign_pointer(q->admin_sched, new_admin);
+		/* Not going to race against advance_sched(), but still */
+		admin = rcu_replace_pointer(q->admin_sched, new_admin,
+					    lockdep_rtnl_is_held());
 		if (admin)
 			call_rcu(&admin->rcu, taprio_free_sched_cb);
 	} else {
-- 
2.45.2