bridge: fdb: add proper lock checks in searching functions

In order to avoid new errors add checks to br_fdb_find and fdb_find_rcu
functions. The first requires hash_lock, the second obviously RCU.
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_fdb.c

@@ -89,6 +89,8 @@ static struct net_bridge_fdb_entry *fdb_find_rcu(struct hlist_head *head,
 {
 	struct net_bridge_fdb_entry *f;
 
+	WARN_ON_ONCE(!rcu_read_lock_held());
+
 	hlist_for_each_entry_rcu(f, head, hlist)
 		if (ether_addr_equal(f->addr.addr, addr) && f->vlan_id == vid)
 			break;
@@ -104,6 +106,8 @@ static struct net_bridge_fdb_entry *br_fdb_find(struct net_bridge *br,
 	struct hlist_head *head = &br->hash[br_mac_hash(addr, vid)];
 	struct net_bridge_fdb_entry *fdb;
 
+	WARN_ON_ONCE(!br_hash_lock_held(br));
+
 	rcu_read_lock();
 	fdb = fdb_find_rcu(head, addr, vid);
 	rcu_read_unlock();

net/bridge/br_private.h

@@ -531,6 +531,15 @@ int br_fdb_external_learn_add(struct net_bridge *br, struct net_bridge_port *p,
 int br_fdb_external_learn_del(struct net_bridge *br, struct net_bridge_port *p,
 			      const unsigned char *addr, u16 vid);
 
+static inline bool br_hash_lock_held(struct net_bridge *br)
+{
+#ifdef CONFIG_LOCKDEP
+	return lockdep_is_held(&br->hash_lock);
+#else
+	return true;
+#endif
+}
+
 /* br_forward.c */
 enum br_pkt_type {
 	BR_PKT_UNICAST,