net: sched: consistently use rcu_replace_pointer() in taprio_change()

[ Upstream commit d5c4546062fd6f5dbce575c7ea52ad66d1968678 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index b284a06b5a75fa3408c4a6515b71ed1a6ec63e78..847e1cc6052ec2a5a5d27a1d65336b25c4092015 100644 (file)
--- 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 {