tunnel: eliminate recursion field

It seems recursion field from "struct ip_tunnel" is not anymore needed.
recursion prevention is done at the upper level (in dev_queue_xmit()),
since we use HARD_TX_LOCK protection for tunnels.

This avoids a cache line ping pong on "struct ip_tunnel" : This structure
should be now mostly read on xmit and receive paths.

Signed-off-by: Eric Dumazet <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/ipip.h

···
 	struct ip_tunnel	*next;
 	struct net_device	*dev;
 
-	int			recursion;	/* Depth of hard_start_xmit recursion */
 	int			err_count;	/* Number of arrived ICMP errors */
 	unsigned long		err_time;	/* Time when the last ICMP error arrived */
 

net/ipv4/ip_gre.c

···
    solution, but it supposes maintaing new variable in ALL
    skb, even if no tunneling is used.
 
-   Current solution: t->recursion lock breaks dead loops. It looks
-   like dev->tbusy flag, but I preferred new variable, because
-   the semantics is different. One day, when hard_start_xmit
-   will be multithreaded we will have to use skb->encapsulation.
+   Current solution: HARD_TX_LOCK lock breaks dead loops.
 
 
 
···
 	__be32 dst;
 	int    mtu;
 
-	if (tunnel->recursion++) {
-		stats->collisions++;
-		goto tx_error;
-	}
-
 	if (dev->type == ARPHRD_ETHER)
 		IPCB(skb)->flags = 0;
 
···
 			ip_rt_put(rt);
 			stats->tx_dropped++;
 			dev_kfree_skb(skb);
-			tunnel->recursion--;
 			return NETDEV_TX_OK;
 		}
 		if (skb->sk)
···
 	nf_reset(skb);
 
 	IPTUNNEL_XMIT();
-	tunnel->recursion--;
 	return NETDEV_TX_OK;
 
 tx_error_icmp:
···
 tx_error:
 	stats->tx_errors++;
 	dev_kfree_skb(skb);
-	tunnel->recursion--;
 	return NETDEV_TX_OK;
 }
 

net/ipv4/ipip.c

···
 	__be32 dst = tiph->daddr;
 	int    mtu;
 
-	if (tunnel->recursion++) {
-		stats->collisions++;
-		goto tx_error;
-	}
-
 	if (skb->protocol != htons(ETH_P_IP))
 		goto tx_error;
 
···
 			ip_rt_put(rt);
 			stats->tx_dropped++;
 			dev_kfree_skb(skb);
-			tunnel->recursion--;
 			return NETDEV_TX_OK;
 		}
 		if (skb->sk)
···
 	nf_reset(skb);
 
 	IPTUNNEL_XMIT();
-	tunnel->recursion--;
 	return NETDEV_TX_OK;
 
 tx_error_icmp:
···
 tx_error:
 	stats->tx_errors++;
 	dev_kfree_skb(skb);
-	tunnel->recursion--;
 	return NETDEV_TX_OK;
 }
 

net/ipv6/ip6_tunnel.c

···
 	struct net_device_stats *stats = &t->dev->stats;
 	int ret;
 
-	if (t->recursion++) {
-		stats->collisions++;
-		goto tx_err;
-	}
-
 	switch (skb->protocol) {
 	case htons(ETH_P_IP):
 		ret = ip4ip6_tnl_xmit(skb, dev);
···
 	if (ret < 0)
 		goto tx_err;
 
-	t->recursion--;
 	return NETDEV_TX_OK;
 
 tx_err:
 	stats->tx_errors++;
 	stats->tx_dropped++;
 	kfree_skb(skb);
-	t->recursion--;
 	return NETDEV_TX_OK;
 }
 

net/ipv6/sit.c

···
 	struct in6_addr *addr6;
 	int addr_type;
 
-	if (tunnel->recursion++) {
-		stats->collisions++;
-		goto tx_error;
-	}
-
 	if (skb->protocol != htons(ETH_P_IPV6))
 		goto tx_error;
 
···
 			ip_rt_put(rt);
 			stats->tx_dropped++;
 			dev_kfree_skb(skb);
-			tunnel->recursion--;
 			return NETDEV_TX_OK;
 		}
 		if (skb->sk)
···
 	nf_reset(skb);
 
 	IPTUNNEL_XMIT();
-	tunnel->recursion--;
 	return NETDEV_TX_OK;
 
 tx_error_icmp:
···
 tx_error:
 	stats->tx_errors++;
 	dev_kfree_skb(skb);
-	tunnel->recursion--;
 	return NETDEV_TX_OK;
 }