netdev - [PATCH net-next v5] net: sched: consistently use rcu_replace_pointer() in taprio

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Message-ID: <20240904115401.3425674-1-dmantipov@yandex.ru>
Date: Wed,  4 Sep 2024 14:54:01 +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>,
	Simon Horman <horms@...nel.org>,
	netdev@...r.kernel.org,
	lvc-project@...uxtesting.org,
	Dmitry Antipov <dmantipov@...dex.ru>
Subject: [PATCH net-next v5] net: sched: consistently use rcu_replace_pointer() in taprio_change()

According to Vinicius (and carefully looking through the whole
https://syzkaller.appspot.com/bug?extid=b65e0af58423fc8a73aa
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>
---
v5: cut from the series, add syzbot link an re-target to net-next
v4: adjust subject to target net tree
v3: unchanged since v2
v2: added to the series
---
 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 cc2df9f8c14a..8498d0606b24 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 {
-- 
2.46.0