udp: gro behind static key

Avoid the socket lookup cost in udp_gro_receive if no socket has a
udp tunnel callback configured.

udp_sk(sk)->gro_receive requires a registration with
setup_udp_tunnel_sock, which enables the static key.
Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/udp.h

@@ -443,8 +443,10 @@ int udpv4_offload_init(void);
 
 void udp_init(void);
 
+DECLARE_STATIC_KEY_FALSE(udp_encap_needed_key);
 void udp_encap_enable(void);
 #if IS_ENABLED(CONFIG_IPV6)
+DECLARE_STATIC_KEY_FALSE(udpv6_encap_needed_key);
 void udpv6_encap_enable(void);
 #endif
 

net/ipv4/udp.c

@@ -1889,7 +1889,7 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 	return 0;
 }
 
-static DEFINE_STATIC_KEY_FALSE(udp_encap_needed_key);
+DEFINE_STATIC_KEY_FALSE(udp_encap_needed_key);
 void udp_encap_enable(void)
 {
 	static_branch_enable(&udp_encap_needed_key);

net/ipv4/udp_offload.c

@@ -405,7 +405,7 @@ static struct sk_buff *udp4_gro_receive(struct list_head *head,
 {
 	struct udphdr *uh = udp_gro_udphdr(skb);
 
-	if (unlikely(!uh))
+	if (unlikely(!uh) || !static_branch_unlikely(&udp_encap_needed_key))
 		goto flush;
 
 	/* Don't bother verifying checksum if we're going to flush anyway. */

net/ipv6/udp.c

@@ -548,7 +548,7 @@ static __inline__ void udpv6_err(struct sk_buff *skb,
 	__udp6_lib_err(skb, opt, type, code, offset, info, &udp_table);
 }
 
-static DEFINE_STATIC_KEY_FALSE(udpv6_encap_needed_key);
+DEFINE_STATIC_KEY_FALSE(udpv6_encap_needed_key);
 void udpv6_encap_enable(void)
 {
 	static_branch_enable(&udpv6_encap_needed_key);

net/ipv6/udp_offload.c

@@ -119,7 +119,7 @@ static struct sk_buff *udp6_gro_receive(struct list_head *head,
 {
 	struct udphdr *uh = udp_gro_udphdr(skb);
 
-	if (unlikely(!uh))
+	if (unlikely(!uh) || !static_branch_unlikely(&udpv6_encap_needed_key))
 		goto flush;
 
 	/* Don't bother verifying checksum if we're going to flush anyway. */