act_sample: get rid of tcf_sample_cleanup_rcu()

Similar to commit d7fb60b9 ("net_sched: get rid of tcfa_rcu"),
TC actions don't need to respect RCU grace period, because it
is either just detached from tc filter (standalone case) or
it is removed together with tc filter (bound case) in which case
RCU grace period is already respected at filter layer.

Fixes: 5c5670fa ("net/sched: Introduce sample tc action")
Reported-by: NEric Dumazet <eric.dumazet@gmail.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Cc: Yotam Gigi <yotamg@mellanox.com>
Signed-off-by: NCong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/tc_act/tc_sample.h

@@ -14,7 +14,6 @@ struct tcf_sample {
 	struct psample_group __rcu *psample_group;
 	u32 psample_group_num;
 	struct list_head tcfm_list;
-	struct rcu_head rcu;
 };
 #define to_sample(a) ((struct tcf_sample *)a)
 

net/sched/act_sample.c

@@ -96,23 +96,16 @@ static int tcf_sample_init(struct net *net, struct nlattr *nla,
 	return ret;
 }
 
-static void tcf_sample_cleanup_rcu(struct rcu_head *rcu)
+static void tcf_sample_cleanup(struct tc_action *a, int bind)
 {
-	struct tcf_sample *s = container_of(rcu, struct tcf_sample, rcu);
+	struct tcf_sample *s = to_sample(a);
 	struct psample_group *psample_group;
 
-	psample_group = rcu_dereference_protected(s->psample_group, 1);
+	psample_group = rtnl_dereference(s->psample_group);
 	RCU_INIT_POINTER(s->psample_group, NULL);
 	psample_group_put(psample_group);
 }
 
-static void tcf_sample_cleanup(struct tc_action *a, int bind)
-{
-	struct tcf_sample *s = to_sample(a);
-
-	call_rcu(&s->rcu, tcf_sample_cleanup_rcu);
-}
-
 static bool tcf_sample_dev_ok_push(struct net_device *dev)
 {
 	switch (dev->type) {
@@ -264,7 +257,6 @@ static int __init sample_init_module(void)
 
 static void __exit sample_cleanup_module(void)
 {
-	rcu_barrier();
 	tcf_unregister_action(&act_sample_ops, &sample_net_ops);
 }