[PATCH v2 net-next 3/7] net/sched: taprio: use rtnl_dereference for oper and admin sched in taprio_destroy()

Vladimir Oltean
2022-09-15T10:51:24Z

Sparse complains that taprio_destroy() dereferences q->oper_sched and
q->admin_sched without rcu_dereference(), since they are marked as __rcu
in the taprio private structure.

1671:28: warning: incorrect type in argument 1 (different address spaces)
1671:28: expected struct callback_head *head
1671:28: got struct callback_head [noderef] __rcu *
1674:28: warning: incorrect type in argument 1 (different address spaces)
1674:28: expected struct callback_head *head
1674:28: got struct callback_head [noderef] __rcu *

To silence that build warning, do actually use rtnl_dereference(), since
we know the rtnl_mutex is held at the time of q->destroy().

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
v1->v2: resend to net-next, use rtnl_dereference() instead of opening an
rcu_read_lock()

net/sched/sch_taprio.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 63cbf856894a..6113c6646559 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -1636,6 +1636,7 @@ static void taprio_destroy(struct Qdisc *sch)
{
struct taprio_sched *q = qdisc_priv(sch);
struct net_device *dev = qdisc_dev(sch);
+ struct sched_gate_list *oper, *admin;
unsigned int i;

spin_lock(&taprio_list_lock);
@@ -1659,11 +1660,14 @@ static void taprio_destroy(struct Qdisc *sch)

netdev_reset_tc(dev);

- if (q->oper_sched)
- call_rcu(&q->oper_sched->rcu, taprio_free_sched_cb);
+ oper = rtnl_dereference(q->oper_sched);
+ admin = rtnl_dereference(q->admin_sched);
+
+ if (oper)
+ call_rcu(&oper->rcu, taprio_free_sched_cb);

- if (q->admin_sched)
- call_rcu(&q->admin_sched->rcu, taprio_free_sched_cb);
+ if (admin)
+ call_rcu(&admin->rcu, taprio_free_sched_cb);
}

static int taprio_init(struct Qdisc *sch, struct nlattr *opt,
--
2.34.1