ipv6: ip6_mc_input() and ip6_mr_input() cleanups

Both functions are always called under RCU.

We remove the extra rcu_read_lock()/rcu_read_unlock().

We use skb_dst_dev_net_rcu() instead of skb_dst_dev_net().

We use dev_net_rcu() instead of dev_net().

Signed-off-by: Eric Dumazet <[e-mail]>
Reviewed-by: Kuniyuki Iwashima <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/ipv6/ip6_input.c

···
 
 int ip6_mc_input(struct sk_buff *skb)
 {
+	struct net_device *dev = skb->dev;
 	int sdif = inet6_sdif(skb);
 	const struct ipv6hdr *hdr;
-	struct net_device *dev;
 	bool deliver;
 
-	__IP6_UPD_PO_STATS(skb_dst_dev_net(skb),
-			 __in6_dev_get_safely(skb->dev), IPSTATS_MIB_INMCAST,
-			 skb->len);
+	__IP6_UPD_PO_STATS(skb_dst_dev_net_rcu(skb),
+			   __in6_dev_get_safely(dev), IPSTATS_MIB_INMCAST,
+			   skb->len);
 
 	/* skb->dev passed may be master dev for vrfs. */
 	if (sdif) {
-		rcu_read_lock();
-		dev = dev_get_by_index_rcu(dev_net(skb->dev), sdif);
+		dev = dev_get_by_index_rcu(dev_net_rcu(dev), sdif);
 		if (!dev) {
-			rcu_read_unlock();
 			kfree_skb(skb);
 			return -ENODEV;
 		}
-	} else {
-		dev = skb->dev;
 	}
 
 	hdr = ipv6_hdr(skb);
 	deliver = ipv6_chk_mcast_addr(dev, &hdr->daddr, NULL);
-	if (sdif)
-		rcu_read_unlock();
 
 #ifdef CONFIG_IPV6_MROUTE
 	/*
 	 *      IPv6 multicast router mode is now supported ;)
 	 */
-	if (atomic_read(&dev_net(skb->dev)->ipv6.devconf_all->mc_forwarding) &&
+	if (atomic_read(&dev_net_rcu(skb->dev)->ipv6.devconf_all->mc_forwarding) &&
 	    !(ipv6_addr_type(&hdr->daddr) &
 	      (IPV6_ADDR_LOOPBACK|IPV6_ADDR_LINKLOCAL)) &&
 	    likely(!(IP6CB(skb)->flags & IP6SKB_FORWARDED))) {
···
 			/* unknown RA - process it normally */
 		}
 
-		if (deliver)
+		if (deliver) {
 			skb2 = skb_clone(skb, GFP_ATOMIC);
-		else {
+		} else {
 			skb2 = skb;
 			skb = NULL;
 		}
 
-		if (skb2) {
+		if (skb2)
 			ip6_mr_input(skb2);
-		}
 	}
 out:
 #endif
-	if (likely(deliver))
+	if (likely(deliver)) {
 		ip6_input(skb);
-	else {
+	} else {
 		/* discard */
 		kfree_skb(skb);
 	}

net/ipv6/ip6mr.c

···
 
 int ip6_mr_input(struct sk_buff *skb)
 {
+	struct net_device *dev = skb->dev;
+	struct net *net = dev_net_rcu(dev);
 	struct mfc6_cache *cache;
-	struct net *net = dev_net(skb->dev);
 	struct mr_table *mrt;
 	struct flowi6 fl6 = {
-		.flowi6_iif	= skb->dev->ifindex,
+		.flowi6_iif	= dev->ifindex,
 		.flowi6_mark	= skb->mark,
 	};
 	int err;
-	struct net_device *dev;
 
 	/* skb->dev passed in is the master dev for vrfs.
 	 * Get the proper interface that does have a vif associated with it.
 	 */
-	dev = skb->dev;
-	if (netif_is_l3_master(skb->dev)) {
+	if (netif_is_l3_master(dev)) {
 		dev = dev_get_by_index_rcu(net, IPCB(skb)->iif);
 		if (!dev) {
 			kfree_skb(skb);