arp: RCU changes

Avoid two atomic ops in arp_fwd_proxy()

Avoid two atomic ops in arp_process()

Valid optims since arp_rcv() is run under rcu_read_lock()
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/arp.c

@@ -545,10 +545,10 @@ static inline int arp_fwd_proxy(struct in_device *in_dev,
 
 	/* place to check for proxy_arp for routes */
 
-	if ((out_dev = in_dev_get(rt->u.dst.dev)) != NULL) {
+	out_dev = __in_dev_get_rcu(rt->u.dst.dev);
+	if (out_dev)
 		omi = IN_DEV_MEDIUM_ID(out_dev);
-		in_dev_put(out_dev);
-	}
+
 	return (omi != imi && omi != -1);
 }
 
@@ -741,7 +741,7 @@ void arp_send(int type, int ptype, __be32 dest_ip,
 static int arp_process(struct sk_buff *skb)
 {
 	struct net_device *dev = skb->dev;
-	struct in_device *in_dev = in_dev_get(dev);
+	struct in_device *in_dev = __in_dev_get_rcu(dev);
 	struct arphdr *arp;
 	unsigned char *arp_ptr;
 	struct rtable *rt;
@@ -890,7 +890,6 @@ static int arp_process(struct sk_buff *skb)
 					arp_send(ARPOP_REPLY,ETH_P_ARP,sip,dev,tip,sha,dev->dev_addr,sha);
 				} else {
 					pneigh_enqueue(&arp_tbl, in_dev->arp_parms, skb);
-					in_dev_put(in_dev);
 					return 0;
 				}
 				goto out;
@@ -936,8 +935,6 @@ static int arp_process(struct sk_buff *skb)
 	}
 
 out:
-	if (in_dev)
-		in_dev_put(in_dev);
 	consume_skb(skb);
 	return 0;
 }