Re: [PATCH net-next V3 3/3] net: Add GRO support for vxlan traffic

On 09/01/2014 00:11, Eric Dumazet wrote:

On Wed, 2014-01-08 at 22:34 +0200, Or Gerlitz wrote:

quoted

+
  /* Notify netdevs that UDP port started listening */
-static void vxlan_notify_add_rx_port(struct sock *sk)
+static void vxlan_notify_add_rx_port(struct vxlan_sock *vs)
  {
  	struct net_device *dev;
+	struct sock *sk = vs->sock->sk;
  	struct net *net = sock_net(sk);
  	sa_family_t sa_family = sk->sk_family;
  	__be16 port = inet_sk(sk)->inet_sport;

@@ -569,12 +671,16 @@ static void vxlan_notify_add_rx_port(struct sock *sk)
  							    port);
  	}
  	rcu_read_unlock();
+
+	if (sa_family == AF_INET)
+		call_rcu(&vs->rcu, vxlan_add_udp_offload);

Why waiting RCU grace period here?

Basically the add operation can be done right away, however, since the 
delete operation can't be done
instantly when we want it, I wanted to protect against a series of 
add/del/add in times T1 < T2 < T3

T1 add(X)
T2 del(X)
T3 add(X)

where the delete is deferred and as a result the 2nd add is done before 
the delete and @ the end offload X is not added in the 2nd time.From 
your other comment below I conclude that I probably miss something about 
the rcu usage here, so will give it further thought.

quoted

  }
  
  /* Notify netdevs that UDP port is no more listening */
-static void vxlan_notify_del_rx_port(struct sock *sk)
+static void vxlan_notify_del_rx_port(struct vxlan_sock *vs)
  {
  	struct net_device *dev;
+	struct sock *sk = vs->sock->sk;
  	struct net *net = sock_net(sk);
  	sa_family_t sa_family = sk->sk_family;
  	__be16 port = inet_sk(sk)->inet_sport;

@@ -586,6 +692,9 @@ static void vxlan_notify_del_rx_port(struct sock *sk)
  							    port);
  	}
  	rcu_read_unlock();
+
+	if (sa_family == AF_INET)
+		call_rcu(&vs->rcu, vxlan_del_udp_offload);
  }

This looks buggy.

You need to :

1) remove the offload structure from list
2) Then wait rcu grace period, and finally free the memory