[3.11.y.z,extended,stable] Patch "packet: fix send path when running with proto == 0" has been added to staging queue

diff --git a/Documentation/networking/packet_mmap.txt b/Documentation/networking/packet_mmap.txt
index 8572796..f56c278 100644
--- a/Documentation/networking/packet_mmap.txt
+++ b/Documentation/networking/packet_mmap.txt
@@ -123,6 +123,16 @@  Transmission process is similar to capture as shown below.
 [shutdown]  close() --------> destruction of the transmission socket and
                               deallocation of all associated resources.

+Socket creation and destruction is also straight forward, and is done
+the same way as in capturing described in the previous paragraph:
+
+ int fd = socket(PF_PACKET, mode, 0);
+
+The protocol can optionally be 0 in case we only want to transmit
+via this socket, which avoids an expensive call to packet_rcv().
+In this case, you also need to bind(2) the TX_RING with sll_protocol = 0
+set. Otherwise, htons(ETH_P_ALL) or any other protocol, for example.
+
 Binding the socket to your network interface is mandatory (with zero copy) to
 know the header size of frames used in the circular buffer.

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 151e8ae..1b6d773 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -237,6 +237,30 @@  struct packet_skb_cb {
 static void __fanout_unlink(struct sock *sk, struct packet_sock *po);
 static void __fanout_link(struct sock *sk, struct packet_sock *po);

+static struct net_device *packet_cached_dev_get(struct packet_sock *po)
+{
+	struct net_device *dev;
+
+	rcu_read_lock();
+	dev = rcu_dereference(po->cached_dev);
+	if (likely(dev))
+		dev_hold(dev);
+	rcu_read_unlock();
+
+	return dev;
+}
+
+static void packet_cached_dev_assign(struct packet_sock *po,
+				     struct net_device *dev)
+{
+	rcu_assign_pointer(po->cached_dev, dev);
+}
+
+static void packet_cached_dev_reset(struct packet_sock *po)
+{
+	RCU_INIT_POINTER(po->cached_dev, NULL);
+}
+
 /* register_prot_hook must be invoked with the po->bind_lock held,
  * or from a context in which asynchronous accesses to the packet
  * socket is not possible (packet_create()).
@@ -246,12 +270,10 @@  static void register_prot_hook(struct sock *sk)
 	struct packet_sock *po = pkt_sk(sk);

 	if (!po->running) {
-		if (po->fanout) {
+		if (po->fanout)
 			__fanout_link(sk, po);
-		} else {
+		else
 			dev_add_pack(&po->prot_hook);
-			rcu_assign_pointer(po->cached_dev, po->prot_hook.dev);
-		}

 		sock_hold(sk);
 		po->running = 1;
@@ -270,12 +292,11 @@  static void __unregister_prot_hook(struct sock *sk, bool sync)
 	struct packet_sock *po = pkt_sk(sk);

 	po->running = 0;
-	if (po->fanout) {
+
+	if (po->fanout)
 		__fanout_unlink(sk, po);
-	} else {
+	else
 		__dev_remove_pack(&po->prot_hook);
-		RCU_INIT_POINTER(po->cached_dev, NULL);
-	}

 	__sock_put(sk);

@@ -2048,19 +2069,6 @@  static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
 	return tp_len;
 }

-static struct net_device *packet_cached_dev_get(struct packet_sock *po)
-{
-	struct net_device *dev;
-
-	rcu_read_lock();
-	dev = rcu_dereference(po->cached_dev);
-	if (dev)
-		dev_hold(dev);
-	rcu_read_unlock();
-
-	return dev;
-}
-
 static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 {
 	struct sk_buff *skb;
@@ -2077,7 +2085,7 @@  static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)

 	mutex_lock(&po->pg_vec_lock);

-	if (saddr == NULL) {
+	if (likely(saddr == NULL)) {
 		dev	= packet_cached_dev_get(po);
 		proto	= po->num;
 		addr	= NULL;
@@ -2231,7 +2239,7 @@  static int packet_snd(struct socket *sock,
 	 *	Get and verify the address.
 	 */

-	if (saddr == NULL) {
+	if (likely(saddr == NULL)) {
 		dev	= packet_cached_dev_get(po);
 		proto	= po->num;
 		addr	= NULL;
@@ -2440,6 +2448,8 @@  static int packet_release(struct socket *sock)

 	spin_lock(&po->bind_lock);
 	unregister_prot_hook(sk, false);
+	packet_cached_dev_reset(po);
+
 	if (po->prot_hook.dev) {
 		dev_put(po->prot_hook.dev);
 		po->prot_hook.dev = NULL;
@@ -2495,14 +2505,17 @@  static int packet_do_bind(struct sock *sk, struct net_device *dev, __be16 protoc

 	spin_lock(&po->bind_lock);
 	unregister_prot_hook(sk, true);
+
 	po->num = protocol;
 	po->prot_hook.type = protocol;
 	if (po->prot_hook.dev)
 		dev_put(po->prot_hook.dev);
-	po->prot_hook.dev = dev;

+	po->prot_hook.dev = dev;
 	po->ifindex = dev ? dev->ifindex : 0;

+	packet_cached_dev_assign(po, dev);
+
 	if (protocol == 0)
 		goto out_unlock;

@@ -2615,7 +2628,8 @@  static int packet_create(struct net *net, struct socket *sock, int protocol,
 	po = pkt_sk(sk);
 	sk->sk_family = PF_PACKET;
 	po->num = proto;
-	RCU_INIT_POINTER(po->cached_dev, NULL);
+
+	packet_cached_dev_reset(po);

 	sk->sk_destruct = packet_sock_destruct;
 	sk_refcnt_debug_inc(sk);
@@ -3370,6 +3384,7 @@  static int packet_notifier(struct notifier_block *this,
 						sk->sk_error_report(sk);
 				}
 				if (msg == NETDEV_UNREGISTER) {
+					packet_cached_dev_reset(po);
 					po->ifindex = -1;
 					if (po->prot_hook.dev)
 						dev_put(po->prot_hook.dev);