net: rcu-ify tcf_proto

rcu'ify tcf_proto this allows calling tc_classify() without holding
any locks. Updaters are protected by RTNL.

This patch prepares the core net_sched infrastracture for running
the classifier/action chains without holding the qdisc lock however
it does nothing to ensure cls_xxx and act_xxx types also work without
locking. Additional patches are required to address the fall out.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
index 7bbbfe1..d8b5ccf 100644
--- a/net/sched/sch_drr.c
+++ b/net/sched/sch_drr.c
@@ -35,7 +35,7 @@
 
 struct drr_sched {
 	struct list_head		active;
-	struct tcf_proto		*filter_list;
+	struct tcf_proto __rcu		*filter_list;
 	struct Qdisc_class_hash		clhash;
 };
 
@@ -184,7 +184,8 @@
 		drr_destroy_class(sch, cl);
 }
 
-static struct tcf_proto **drr_tcf_chain(struct Qdisc *sch, unsigned long cl)
+static struct tcf_proto __rcu **drr_tcf_chain(struct Qdisc *sch,
+					      unsigned long cl)
 {
 	struct drr_sched *q = qdisc_priv(sch);
 
@@ -319,6 +320,7 @@
 	struct drr_sched *q = qdisc_priv(sch);
 	struct drr_class *cl;
 	struct tcf_result res;
+	struct tcf_proto *fl;
 	int result;
 
 	if (TC_H_MAJ(skb->priority ^ sch->handle) == 0) {
@@ -328,7 +330,8 @@
 	}
 
 	*qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
-	result = tc_classify(skb, q->filter_list, &res);
+	fl = rcu_dereference_bh(q->filter_list);
+	result = tc_classify(skb, fl, &res);
 	if (result >= 0) {
 #ifdef CONFIG_NET_CLS_ACT
 		switch (result) {