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 cc2df9f8c14a6839fed9f1dab33831bff2de105a..8498d0606b248b6e0aeb27950d07efc4bc2de441 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 {