net: bridge: fdb: eliminate extra port state tests from fast-path

When commit df1c0b84 ("[BRIDGE]: Packets leaking out of
disabled/blocked ports.") introduced the port state tests in
br_fdb_update() it was to avoid learning/refreshing from STP BPDUs, it was
also used to avoid learning/refreshing from user-space with NTF_USE. Those
two tests are done for every packet entering the bridge if it's learning,
but for the fast-path we already have them checked in br_handle_frame() and
is unnecessary to do it again. Thus push the checks to the unlikely cases
and drop them from br_fdb_update(), the new nbp_state_should_learn() helper
is used to determine if the port state allows br_fdb_update() to be called.
The two places which need to do it manually are:
 - user-space add call with NTF_USE set
 - link-local packet learning done in __br_handle_local_finish()
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_fdb.c

@@ -566,11 +566,6 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
 	if (hold_time(br) == 0)
 		return;
 
-	/* ignore packets unless we are using this port */
-	if (!(source->state == BR_STATE_LEARNING ||
-	      source->state == BR_STATE_FORWARDING))
-		return;
-
 	fdb = fdb_find_rcu(&br->fdb_hash_tbl, addr, vid);
 	if (likely(fdb)) {
 		/* attempt to update an entry for a local interface */
@@ -886,6 +881,9 @@ static int __br_fdb_add(struct ndmsg *ndm, struct net_bridge *br,
 				br->dev->name);
 			return -EINVAL;
 		}
+		if (!nbp_state_should_learn(p))
+			return 0;
+
 		local_bh_disable();
 		rcu_read_lock();
 		br_fdb_update(br, p, addr, vid, BIT(BR_FDB_ADDED_BY_USER));

net/bridge/br_input.c

@@ -182,6 +182,7 @@ static void __br_handle_local_finish(struct sk_buff *skb)
 
 	/* check if vlan is allowed, to avoid spoofing */
 	if ((p->flags & BR_LEARNING) &&
+	    nbp_state_should_learn(p) &&
 	    !br_opt_get(p->br, BROPT_NO_LL_LEARN) &&
 	    br_should_learn(p, skb, &vid))
 		br_fdb_update(p->br, p, eth_hdr(skb)->h_source, vid, 0);

net/bridge/br_private.h

@@ -500,6 +500,11 @@ static inline bool br_vlan_should_use(const struct net_bridge_vlan *v)
 	return true;
 }
 
+static inline bool nbp_state_should_learn(const struct net_bridge_port *p)
+{
+	return p->state == BR_STATE_LEARNING || p->state == BR_STATE_FORWARDING;
+}
+
 static inline int br_opt_get(const struct net_bridge *br,
 			     enum net_bridge_opts opt)
 {