ndisc: ndisc_send_redirect() cleanup

ndisc_send_redirect() is always called under rcu_read_lock().

It can use dev_net_rcu() and avoid one redundant
rcu_read_lock()/rcu_read_unlock() pair.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20250214140705.2105890-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv6/ndisc.c

@@ -1680,7 +1680,7 @@ static void ndisc_fill_redirect_hdr_option(struct sk_buff *skb,
 void ndisc_send_redirect(struct sk_buff *skb, const struct in6_addr *target)
 {
 	struct net_device *dev = skb->dev;
-	struct net *net = dev_net(dev);
+	struct net *net = dev_net_rcu(dev);
 	struct sock *sk = net->ipv6.ndisc_sk;
 	int optlen = 0;
 	struct inet_peer *peer;
@@ -1695,8 +1695,8 @@ void ndisc_send_redirect(struct sk_buff *skb, const struct in6_addr *target)
 	   ops_data_buf[NDISC_OPS_REDIRECT_DATA_SPACE], *ops_data = NULL;
 	bool ret;
 
-	if (netif_is_l3_master(skb->dev)) {
-		dev = dev_get_by_index_rcu(dev_net(skb->dev), IPCB(skb)->iif);
+	if (netif_is_l3_master(dev)) {
+		dev = dev_get_by_index_rcu(net, IPCB(skb)->iif);
 		if (!dev)
 			return;
 	}
@@ -1734,10 +1734,8 @@ void ndisc_send_redirect(struct sk_buff *skb, const struct in6_addr *target)
 		goto release;
 	}
 
-	rcu_read_lock();
 	peer = inet_getpeer_v6(net->ipv6.peers, &ipv6_hdr(skb)->saddr);
 	ret = inet_peer_xrlim_allow(peer, 1*HZ);
-	rcu_read_unlock();
 
 	if (!ret)
 		goto release;