[NETNS]: Make netns refconting debug like a socket one.

Make release_net/hold_net noop for performance-hungry people. This is a debug
staff and should be used in the debug mode only.

Add check for net != NULL in hold/release calls. This will be required
later on.

[ Added minor simplifications suggested by Brian Haley. -DaveM ]
Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/net_namespace.h

@@ -26,9 +26,11 @@ struct net {
 	atomic_t		count;		/* To decided when the network
 						 *  namespace should be freed.
 						 */
+#ifdef NETNS_REFCNT_DEBUG
 	atomic_t		use_count;	/* To track references we
 						 * destroy on demand
 						 */
+#endif
 	struct list_head	list;		/* list of network namespaces */
 	struct work_struct	work;		/* work struct for freeing */
 
@@ -117,17 +119,6 @@ static inline void put_net(struct net *net)
 		__put_net(net);
 }
 
-static inline struct net *hold_net(struct net *net)
-{
-	atomic_inc(&net->use_count);
-	return net;
-}
-
-static inline void release_net(struct net *net)
-{
-	atomic_dec(&net->use_count);
-}
-
 static inline
 int net_eq(const struct net *net1, const struct net *net2)
 {
@@ -143,27 +134,44 @@ static inline void put_net(struct net *net)
 {
 }
 
+static inline struct net *maybe_get_net(struct net *net)
+{
+	return net;
+}
+
+static inline
+int net_eq(const struct net *net1, const struct net *net2)
+{
+	return 1;
+}
+#endif
+
+
+#ifdef NETNS_REFCNT_DEBUG
 static inline struct net *hold_net(struct net *net)
 {
+	if (net)
+		atomic_inc(&net->use_count);
 	return net;
 }
 
 static inline void release_net(struct net *net)
 {
+	if (net)
+		atomic_dec(&net->use_count);
 }
-
-static inline struct net *maybe_get_net(struct net *net)
+#else
+static inline struct net *hold_net(struct net *net)
 {
 	return net;
 }
 
-static inline
-int net_eq(const struct net *net1, const struct net *net2)
+static inline void release_net(struct net *net)
 {
-	return 1;
 }
 #endif
 
+
 #define for_each_net(VAR)				\
 	list_for_each_entry(VAR, &net_namespace_list, list)
 

net/core/net_namespace.c

@@ -35,7 +35,9 @@ static __net_init int setup_net(struct net *net)
 	struct net_generic *ng;
 
 	atomic_set(&net->count, 1);
+#ifdef NETNS_REFCNT_DEBUG
 	atomic_set(&net->use_count, 0);
+#endif
 
 	error = -ENOMEM;
 	ng = kzalloc(sizeof(struct net_generic) +
@@ -86,11 +88,13 @@ static void net_free(struct net *net)
 	if (!net)
 		return;
 
+#ifdef NETNS_REFCNT_DEBUG
 	if (unlikely(atomic_read(&net->use_count) != 0)) {
 		printk(KERN_EMERG "network namespace not free! Usage: %d\n",
 			atomic_read(&net->use_count));
 		return;
 	}
+#endif
 
 	kmem_cache_free(net_cachep, net);
 }