ipip: convert hash tables locking to RCU

IPIP tunnels use one rwlock to protect their hash tables.

This locking scheme can be converted to RCU for free, since netdevice
already must wait for a RCU grace period at dismantle time.
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/ipip.c

@@ -134,7 +134,13 @@ static void ipip_fb_tunnel_init(struct net_device *dev);
 static void ipip_tunnel_init(struct net_device *dev);
 static void ipip_tunnel_setup(struct net_device *dev);
 
-static DEFINE_RWLOCK(ipip_lock);
+/*
+ * Locking : hash tables are protected by RCU and a spinlock
+ */
+static DEFINE_SPINLOCK(ipip_lock);
+
+#define for_each_ip_tunnel_rcu(start) \
+	for (t = rcu_dereference(start); t; t = rcu_dereference(t->next))
 
 static struct ip_tunnel * ipip_tunnel_lookup(struct net *net,
 		__be32 remote, __be32 local)
@@ -144,20 +150,21 @@ static struct ip_tunnel * ipip_tunnel_lookup(struct net *net,
 	struct ip_tunnel *t;
 	struct ipip_net *ipn = net_generic(net, ipip_net_id);
 
-	for (t = ipn->tunnels_r_l[h0^h1]; t; t = t->next) {
+	for_each_ip_tunnel_rcu(ipn->tunnels_r_l[h0 ^ h1])
 		if (local == t->parms.iph.saddr &&
 		    remote == t->parms.iph.daddr && (t->dev->flags&IFF_UP))
 			return t;
-	}
-	for (t = ipn->tunnels_r[h0]; t; t = t->next) {
+
+	for_each_ip_tunnel_rcu(ipn->tunnels_r[h0])
 		if (remote == t->parms.iph.daddr && (t->dev->flags&IFF_UP))
 			return t;
-	}
-	for (t = ipn->tunnels_l[h1]; t; t = t->next) {
+
+	for_each_ip_tunnel_rcu(ipn->tunnels_l[h1])
 		if (local == t->parms.iph.saddr && (t->dev->flags&IFF_UP))
 			return t;
-	}
-	if ((t = ipn->tunnels_wc[0]) != NULL && (t->dev->flags&IFF_UP))
+
+	t = rcu_dereference(ipn->tunnels_wc[0]);
+	if (t && (t->dev->flags&IFF_UP))
 		return t;
 	return NULL;
 }
@@ -193,9 +200,9 @@ static void ipip_tunnel_unlink(struct ipip_net *ipn, struct ip_tunnel *t)
 
 	for (tp = ipip_bucket(ipn, t); *tp; tp = &(*tp)->next) {
 		if (t == *tp) {
-			write_lock_bh(&ipip_lock);
+			spin_lock_bh(&ipip_lock);
 			*tp = t->next;
-			write_unlock_bh(&ipip_lock);
+			spin_unlock_bh(&ipip_lock);
 			break;
 		}
 	}
@@ -205,10 +212,10 @@ static void ipip_tunnel_link(struct ipip_net *ipn, struct ip_tunnel *t)
 {
 	struct ip_tunnel **tp = ipip_bucket(ipn, t);
 
+	spin_lock_bh(&ipip_lock);
 	t->next = *tp;
-	write_lock_bh(&ipip_lock);
-	*tp = t;
-	write_unlock_bh(&ipip_lock);
+	rcu_assign_pointer(*tp, t);
+	spin_unlock_bh(&ipip_lock);
 }
 
 static struct ip_tunnel * ipip_tunnel_locate(struct net *net,
@@ -267,9 +274,9 @@ static void ipip_tunnel_uninit(struct net_device *dev)
 	struct ipip_net *ipn = net_generic(net, ipip_net_id);
 
 	if (dev == ipn->fb_tunnel_dev) {
-		write_lock_bh(&ipip_lock);
+		spin_lock_bh(&ipip_lock);
 		ipn->tunnels_wc[0] = NULL;
-		write_unlock_bh(&ipip_lock);
+		spin_unlock_bh(&ipip_lock);
 	} else
 		ipip_tunnel_unlink(ipn, netdev_priv(dev));
 	dev_put(dev);
@@ -318,7 +325,7 @@ static int ipip_err(struct sk_buff *skb, u32 info)
 
 	err = -ENOENT;
 
-	read_lock(&ipip_lock);
+	rcu_read_lock();
 	t = ipip_tunnel_lookup(dev_net(skb->dev), iph->daddr, iph->saddr);
 	if (t == NULL || t->parms.iph.daddr == 0)
 		goto out;
@@ -333,7 +340,7 @@ static int ipip_err(struct sk_buff *skb, u32 info)
 		t->err_count = 1;
 	t->err_time = jiffies;
 out:
-	read_unlock(&ipip_lock);
+	rcu_read_unlock();
 	return err;
 }
 
@@ -351,11 +358,11 @@ static int ipip_rcv(struct sk_buff *skb)
 	struct ip_tunnel *tunnel;
 	const struct iphdr *iph = ip_hdr(skb);
 
-	read_lock(&ipip_lock);
+	rcu_read_lock();
 	if ((tunnel = ipip_tunnel_lookup(dev_net(skb->dev),
 					iph->saddr, iph->daddr)) != NULL) {
 		if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
-			read_unlock(&ipip_lock);
+			rcu_read_unlock();
 			kfree_skb(skb);
 			return 0;
 		}
@@ -374,10 +381,10 @@ static int ipip_rcv(struct sk_buff *skb)
 		nf_reset(skb);
 		ipip_ecn_decapsulate(iph, skb);
 		netif_rx(skb);
-		read_unlock(&ipip_lock);
+		rcu_read_unlock();
 		return 0;
 	}
-	read_unlock(&ipip_lock);
+	rcu_read_unlock();
 
 	return -1;
 }