From: Dmitry Antipov <dmantipov@yandex.ru>
Date: Wed, 4 Sep 2024 11:54:01 +0000 (+0300)
Subject: net: sched: consistently use rcu_replace_pointer() in taprio_change()
X-Git-Tag: microblaze-v6.13~235^2~75
X-Git-Url: http://git.monstr.eu/?a=commitdiff_plain;h=d5c4546062fd6f5dbce575c7ea52ad66d1968678;p=linux-2.6-microblaze.git

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@intel.com>
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

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 {