openvswitch: Refactor get_dp() function into multiple access APIs.

Avoid recursive read_rcu_lock() by using the lighter weight
get_dp_rcu() API. Add proper locking assertions to get_dp().
Signed-off-by: Andy Zhou <azhou@nicira.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>

net/openvswitch/datapath.c

@@ -140,19 +140,30 @@ static int queue_gso_packets(struct datapath *dp, struct sk_buff *,
 static int queue_userspace_packet(struct datapath *dp, struct sk_buff *,
 				  const struct dp_upcall_info *);
 
-/* Must be called with rcu_read_lock or ovs_mutex. */
-static struct datapath *get_dp(struct net *net, int dp_ifindex)
+/* Must be called with rcu_read_lock. */
+static struct datapath *get_dp_rcu(struct net *net, int dp_ifindex)
 {
-	struct datapath *dp = NULL;
-	struct net_device *dev;
+	struct net_device *dev = dev_get_by_index_rcu(net, dp_ifindex);
 
-	rcu_read_lock();
-	dev = dev_get_by_index_rcu(net, dp_ifindex);
 	if (dev) {
 		struct vport *vport = ovs_internal_dev_get_vport(dev);
 		if (vport)
-			dp = vport->dp;
+			return vport->dp;
 	}
+
+	return NULL;
+}
+
+/* The caller must hold either ovs_mutex or rcu_read_lock to keep the
+ * returned dp pointer valid.
+ */
+static inline struct datapath *get_dp(struct net *net, int dp_ifindex)
+{
+	struct datapath *dp;
+
+	WARN_ON_ONCE(!rcu_read_lock_held() && !lockdep_ovsl_is_held());
+	rcu_read_lock();
+	dp = get_dp_rcu(net, dp_ifindex);
 	rcu_read_unlock();
 
 	return dp;
@@ -573,7 +584,7 @@ static int ovs_packet_cmd_execute(struct sk_buff *skb, struct genl_info *info)
 	packet->mark = flow->key.phy.skb_mark;
 
 	rcu_read_lock();
-	dp = get_dp(sock_net(skb->sk), ovs_header->dp_ifindex);
+	dp = get_dp_rcu(sock_net(skb->sk), ovs_header->dp_ifindex);
 	err = -ENODEV;
 	if (!dp)
 		goto err_unlock;
@@ -1227,7 +1238,7 @@ static int ovs_flow_cmd_dump(struct sk_buff *skb, struct netlink_callback *cb)
 	struct datapath *dp;
 
 	rcu_read_lock();
-	dp = get_dp(sock_net(skb->sk), ovs_header->dp_ifindex);
+	dp = get_dp_rcu(sock_net(skb->sk), ovs_header->dp_ifindex);
 	if (!dp) {
 		rcu_read_unlock();
 		return -ENODEV;
@@ -1989,7 +2000,7 @@ static int ovs_vport_cmd_dump(struct sk_buff *skb, struct netlink_callback *cb)
 	int i, j = 0;
 
 	rcu_read_lock();
-	dp = get_dp(sock_net(skb->sk), ovs_header->dp_ifindex);
+	dp = get_dp_rcu(sock_net(skb->sk), ovs_header->dp_ifindex);
 	if (!dp) {
 		rcu_read_unlock();
 		return -ENODEV;