ipv6 sit: RCU conversion phase II

SIT 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: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 27 insertions, 18 deletions

diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index 8cdcc2ad048c..b6b16264b305 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -77,8 +77,17 @@ struct sit_net {
         struct net_device *fb_tunnel_dev;
 };
 
-static DEFINE_RWLOCK(ipip6_lock);
+/*
+ * Locking : hash tables are protected by RCU and a spinlock
+ */
+static DEFINE_SPINLOCK(ipip6_lock);
+
+#define for_each_ip_tunnel_rcu(start) \
+        for (t = rcu_dereference(start); t; t = rcu_dereference(t->next))
 
+/*
+ * Must be invoked with rcu_read_lock
+ */
 static struct ip_tunnel * ipip6_tunnel_lookup(struct net *net,
                 struct net_device *dev, __be32 remote, __be32 local)
 {
@@ -87,26 +96,26 @@ static struct ip_tunnel * ipip6_tunnel_lookup(struct net *net,
         struct ip_tunnel *t;
         struct sit_net *sitn = net_generic(net, sit_net_id);
 
-        for (t = sitn->tunnels_r_l[h0^h1]; t; t = t->next) {
+        for_each_ip_tunnel_rcu(sitn->tunnels_r_l[h0 ^ h1]) {
                 if (local == t->parms.iph.saddr &&
                     remote == t->parms.iph.daddr &&
                     (!dev || !t->parms.link || dev->iflink == t->parms.link) &&
                     (t->dev->flags & IFF_UP))
                         return t;
         }
-        for (t = sitn->tunnels_r[h0]; t; t = t->next) {
+        for_each_ip_tunnel_rcu(sitn->tunnels_r[h0]) {
                 if (remote == t->parms.iph.daddr &&
                     (!dev || !t->parms.link || dev->iflink == t->parms.link) &&
                     (t->dev->flags & IFF_UP))
                         return t;
         }
-        for (t = sitn->tunnels_l[h1]; t; t = t->next) {
+        for_each_ip_tunnel_rcu(sitn->tunnels_l[h1]) {
                 if (local == t->parms.iph.saddr &&
                     (!dev || !t->parms.link || dev->iflink == t->parms.link) &&
                     (t->dev->flags & IFF_UP))
                         return t;
         }
-        t = sitn->tunnels_wc[0];
+        t = rcu_dereference(sitn->tunnels_wc[0]);
         if ((t != NULL) && (t->dev->flags & IFF_UP))
                 return t;
         return NULL;
@@ -143,9 +152,9 @@ static void ipip6_tunnel_unlink(struct sit_net *sitn, struct ip_tunnel *t)
 
         for (tp = ipip6_bucket(sitn, t); *tp; tp = &(*tp)->next) {
                 if (t == *tp) {
-                        write_lock_bh(&ipip6_lock);
+                        spin_lock_bh(&ipip6_lock);
                         *tp = t->next;
-                        write_unlock_bh(&ipip6_lock);
+                        spin_unlock_bh(&ipip6_lock);
                         break;
                 }
         }
@@ -155,10 +164,10 @@ static void ipip6_tunnel_link(struct sit_net *sitn, struct ip_tunnel *t)
 {
         struct ip_tunnel **tp = ipip6_bucket(sitn, t);
 
+        spin_lock_bh(&ipip6_lock);
         t->next = *tp;
-        write_lock_bh(&ipip6_lock);
-        *tp = t;
-        write_unlock_bh(&ipip6_lock);
+        rcu_assign_pointer(*tp, t);
+        spin_unlock_bh(&ipip6_lock);
 }
 
 static void ipip6_tunnel_clone_6rd(struct net_device *dev, struct sit_net *sitn)
@@ -447,9 +456,9 @@ static void ipip6_tunnel_uninit(struct net_device *dev)
         struct sit_net *sitn = net_generic(net, sit_net_id);
 
         if (dev == sitn->fb_tunnel_dev) {
-                write_lock_bh(&ipip6_lock);
+                spin_lock_bh(&ipip6_lock);
                 sitn->tunnels_wc[0] = NULL;
-                write_unlock_bh(&ipip6_lock);
+                spin_unlock_bh(&ipip6_lock);
                 dev_put(dev);
         } else {
                 ipip6_tunnel_unlink(sitn, netdev_priv(dev));
@@ -502,7 +511,7 @@ static int ipip6_err(struct sk_buff *skb, u32 info)
 
         err = -ENOENT;
 
-        read_lock(&ipip6_lock);
+        rcu_read_lock();
         t = ipip6_tunnel_lookup(dev_net(skb->dev),
                                 skb->dev,
                                 iph->daddr,
@@ -520,7 +529,7 @@ static int ipip6_err(struct sk_buff *skb, u32 info)
                 t->err_count = 1;
         t->err_time = jiffies;
 out:
-        read_unlock(&ipip6_lock);
+        rcu_read_unlock();
         return err;
 }
 
@@ -540,7 +549,7 @@ static int ipip6_rcv(struct sk_buff *skb)
 
         iph = ip_hdr(skb);
 
-        read_lock(&ipip6_lock);
+        rcu_read_lock();
         tunnel = ipip6_tunnel_lookup(dev_net(skb->dev), skb->dev,
                                      iph->saddr, iph->daddr);
         if (tunnel != NULL) {
@@ -554,7 +563,7 @@ static int ipip6_rcv(struct sk_buff *skb)
                 if ((tunnel->dev->priv_flags & IFF_ISATAP) &&
                     !isatap_chksrc(skb, iph, tunnel)) {
                         tunnel->dev->stats.rx_errors++;
-                        read_unlock(&ipip6_lock);
+                        rcu_read_unlock();
                         kfree_skb(skb);
                         return 0;
                 }
@@ -565,12 +574,12 @@ static int ipip6_rcv(struct sk_buff *skb)
                 nf_reset(skb);
                 ipip6_ecn_decapsulate(iph, skb);
                 netif_rx(skb);
-                read_unlock(&ipip6_lock);
+                rcu_read_unlock();
                 return 0;
         }
 
         icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);
-        read_unlock(&ipip6_lock);
+        rcu_read_unlock();
 out:
         kfree_skb(skb);
         return 0;