ip6tnl: convert hash tables locking to RCU

ip6_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, 25 insertions, 19 deletions

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index c595bbe1ed99..670c291d2567 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -88,8 +88,10 @@ struct ip6_tnl_net {
         struct ip6_tnl **tnls[2];
 };
 
-/* lock for the tunnel lists */
-static DEFINE_RWLOCK(ip6_tnl_lock);
+/*
+ * Locking : hash tables are protected by RCU and a spinlock
+ */
+static DEFINE_SPINLOCK(ip6_tnl_lock);
 
 static inline struct dst_entry *ip6_tnl_dst_check(struct ip6_tnl *t)
 {
@@ -130,6 +132,9 @@ static inline void ip6_tnl_dst_store(struct ip6_tnl *t, struct dst_entry *dst)
  *   else %NULL
  **/
 
+#define for_each_ip6_tunnel_rcu(start) \
+        for (t = rcu_dereference(start); t; t = rcu_dereference(t->next))
+
 static struct ip6_tnl *
 ip6_tnl_lookup(struct net *net, struct in6_addr *remote, struct in6_addr *local)
 {
@@ -138,13 +143,14 @@ ip6_tnl_lookup(struct net *net, struct in6_addr *remote, struct in6_addr *local)
         struct ip6_tnl *t;
         struct ip6_tnl_net *ip6n = net_generic(net, ip6_tnl_net_id);
 
-        for (t = ip6n->tnls_r_l[h0 ^ h1]; t; t = t->next) {
+        for_each_ip6_tunnel_rcu(ip6n->tnls_r_l[h0 ^ h1]) {
                 if (ipv6_addr_equal(local, &t->parms.laddr) &&
                     ipv6_addr_equal(remote, &t->parms.raddr) &&
                     (t->dev->flags & IFF_UP))
                         return t;
         }
-        if ((t = ip6n->tnls_wc[0]) != NULL && (t->dev->flags & IFF_UP))
+        t = rcu_dereference(ip6n->tnls_wc[0]);
+        if (t && (t->dev->flags & IFF_UP))
                 return t;
 
         return NULL;
@@ -186,10 +192,10 @@ ip6_tnl_link(struct ip6_tnl_net *ip6n, struct ip6_tnl *t)
 {
         struct ip6_tnl **tp = ip6_tnl_bucket(ip6n, &t->parms);
 
+        spin_lock_bh(&ip6_tnl_lock);
         t->next = *tp;
-        write_lock_bh(&ip6_tnl_lock);
-        *tp = t;
-        write_unlock_bh(&ip6_tnl_lock);
+        rcu_assign_pointer(*tp, t);
+        spin_unlock_bh(&ip6_tnl_lock);
 }
 
 /**
@@ -204,9 +210,9 @@ ip6_tnl_unlink(struct ip6_tnl_net *ip6n, struct ip6_tnl *t)
 
         for (tp = ip6_tnl_bucket(ip6n, &t->parms); *tp; tp = &(*tp)->next) {
                 if (t == *tp) {
-                        write_lock_bh(&ip6_tnl_lock);
+                        spin_lock_bh(&ip6_tnl_lock);
                         *tp = t->next;
-                        write_unlock_bh(&ip6_tnl_lock);
+                        spin_unlock_bh(&ip6_tnl_lock);
                         break;
                 }
         }
@@ -313,9 +319,9 @@ ip6_tnl_dev_uninit(struct net_device *dev)
         struct ip6_tnl_net *ip6n = net_generic(net, ip6_tnl_net_id);
 
         if (dev == ip6n->fb_tnl_dev) {
-                write_lock_bh(&ip6_tnl_lock);
+                spin_lock_bh(&ip6_tnl_lock);
                 ip6n->tnls_wc[0] = NULL;
-                write_unlock_bh(&ip6_tnl_lock);
+                spin_unlock_bh(&ip6_tnl_lock);
         } else {
                 ip6_tnl_unlink(ip6n, t);
         }
@@ -409,7 +415,7 @@ ip6_tnl_err(struct sk_buff *skb, __u8 ipproto, struct inet6_skb_parm *opt,
            in trouble since we might need the source address for further
            processing of the error. */
 
-        read_lock(&ip6_tnl_lock);
+        rcu_read_lock();
         if ((t = ip6_tnl_lookup(dev_net(skb->dev), &ipv6h->daddr,
                                         &ipv6h->saddr)) == NULL)
                 goto out;
@@ -482,7 +488,7 @@ ip6_tnl_err(struct sk_buff *skb, __u8 ipproto, struct inet6_skb_parm *opt,
         *msg = rel_msg;
 
 out:
-        read_unlock(&ip6_tnl_lock);
+        rcu_read_unlock();
         return err;
 }
 
@@ -693,23 +699,23 @@ static int ip6_tnl_rcv(struct sk_buff *skb, __u16 protocol,
         struct ip6_tnl *t;
         struct ipv6hdr *ipv6h = ipv6_hdr(skb);
 
-        read_lock(&ip6_tnl_lock);
+        rcu_read_lock();
 
         if ((t = ip6_tnl_lookup(dev_net(skb->dev), &ipv6h->saddr,
                                         &ipv6h->daddr)) != NULL) {
                 if (t->parms.proto != ipproto && t->parms.proto != 0) {
-                        read_unlock(&ip6_tnl_lock);
+                        rcu_read_unlock();
                         goto discard;
                 }
 
                 if (!xfrm6_policy_check(NULL, XFRM_POLICY_IN, skb)) {
-                        read_unlock(&ip6_tnl_lock);
+                        rcu_read_unlock();
                         goto discard;
                 }
 
                 if (!ip6_tnl_rcv_ctl(t)) {
                         t->dev->stats.rx_dropped++;
-                        read_unlock(&ip6_tnl_lock);
+                        rcu_read_unlock();
                         goto discard;
                 }
                 secpath_reset(skb);
@@ -727,10 +733,10 @@ static int ip6_tnl_rcv(struct sk_buff *skb, __u16 protocol,
                 t->dev->stats.rx_packets++;
                 t->dev->stats.rx_bytes += skb->len;
                 netif_rx(skb);
-                read_unlock(&ip6_tnl_lock);
+                rcu_read_unlock();
                 return 0;
         }
-        read_unlock(&ip6_tnl_lock);
+        rcu_read_unlock();
         return 1;
 
 discard: