[IPV6]: Remove ndiscs rt6_lock dependency

(Ab)using rt6_lock wouldn't work anymore if rt6_lock is
converted into a per table lock.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -747,8 +747,6 @@ static void ip6_rt_update_pmtu(struct dst_entry *dst, u32 mtu)
 	}
 }
 
-/* Protected by rt6_lock.  */
-static struct dst_entry *ndisc_dst_gc_list;
 static int ipv6_get_mtu(struct net_device *dev);
 
 static inline unsigned int ipv6_advmss(unsigned int mtu)
@@ -769,6 +767,9 @@ static inline unsigned int ipv6_advmss(unsigned int mtu)
 	return mtu;
 }
 
+static struct dst_entry *ndisc_dst_gc_list;
+DEFINE_SPINLOCK(ndisc_lock);
+
 struct dst_entry *ndisc_dst_alloc(struct net_device *dev, 
 				  struct neighbour *neigh,
 				  struct in6_addr *addr,
@@ -809,10 +810,10 @@ struct dst_entry *ndisc_dst_alloc(struct net_device *dev,
 	rt->rt6i_dst.plen = 128;
 #endif
 
-	write_lock_bh(&rt6_lock);
+	spin_lock_bh(&ndisc_lock);
 	rt->u.dst.next = ndisc_dst_gc_list;
 	ndisc_dst_gc_list = &rt->u.dst;
-	write_unlock_bh(&rt6_lock);
+	spin_unlock_bh(&ndisc_lock);
 
 	fib6_force_start_gc();
 
@@ -826,8 +827,11 @@ int ndisc_dst_gc(int *more)
 	int freed;
 
 	next = NULL;
-	pprev = &ndisc_dst_gc_list;
  	freed = 0;
+
+	spin_lock_bh(&ndisc_lock);
+	pprev = &ndisc_dst_gc_list;
+
 	while ((dst = *pprev) != NULL) {
 		if (!atomic_read(&dst->__refcnt)) {
 			*pprev = dst->next;
@@ -839,6 +843,8 @@ int ndisc_dst_gc(int *more)
 		}
 	}
 
+	spin_unlock_bh(&ndisc_lock);
+
 	return freed;
 }