udp: use atomic_inc_not_zero_hint

UDP sockets refcount is usually 2, unless an incoming frame is going to
be queued in receive or backlog queue.

Using atomic_inc_not_zero_hint() permits to reduce latency, because
processor issues less memory transactions.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -57,7 +57,7 @@
 #include <linux/rculist_nulls.h>
 #include <linux/poll.h>
 
-#include <asm/atomic.h>
+#include <linux/atomic.h>
 #include <net/dst.h>
 #include <net/checksum.h>
 

net/ipv4/udp.c

@@ -430,7 +430,7 @@ static struct sock *udp4_lib_lookup2(struct net *net,
 
 	if (result) {
 exact_match:
-		if (unlikely(!atomic_inc_not_zero(&result->sk_refcnt)))
+		if (unlikely(!atomic_inc_not_zero_hint(&result->sk_refcnt, 2)))
 			result = NULL;
 		else if (unlikely(compute_score2(result, net, saddr, sport,
 				  daddr, hnum, dif) < badness)) {
@@ -500,7 +500,7 @@ static struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
 		goto begin;
 
 	if (result) {
-		if (unlikely(!atomic_inc_not_zero(&result->sk_refcnt)))
+		if (unlikely(!atomic_inc_not_zero_hint(&result->sk_refcnt, 2)))
 			result = NULL;
 		else if (unlikely(compute_score(result, net, saddr, hnum, sport,
 				  daddr, dport, dif) < badness)) {

net/ipv6/udp.c

@@ -227,7 +227,7 @@ static struct sock *udp6_lib_lookup2(struct net *net,
 
 	if (result) {
 exact_match:
-		if (unlikely(!atomic_inc_not_zero(&result->sk_refcnt)))
+		if (unlikely(!atomic_inc_not_zero_hint(&result->sk_refcnt, 2)))
 			result = NULL;
 		else if (unlikely(compute_score2(result, net, saddr, sport,
 				  daddr, hnum, dif) < badness)) {
@@ -294,7 +294,7 @@ static struct sock *__udp6_lib_lookup(struct net *net,
 		goto begin;
 
 	if (result) {
-		if (unlikely(!atomic_inc_not_zero(&result->sk_refcnt)))
+		if (unlikely(!atomic_inc_not_zero_hint(&result->sk_refcnt, 2)))
 			result = NULL;
 		else if (unlikely(compute_score(result, net, hnum, saddr, sport,
 					daddr, dport, dif) < badness)) {