Delay struct net freeing while there's a sysfs instance refering to it

	* new refcount in struct net, controlling actual freeing of the memory
	* new method in kobj_ns_type_operations (->drop_ns())
	* ->current_ns() semantics change - it's supposed to be followed by
corresponding ->drop_ns().  For struct net in case of CONFIG_NET_NS it bumps
the new refcount; net_drop_ns() decrements it and calls net_free() if the
last reference has been dropped.  Method renamed to ->grab_current_ns().
	* old net_free() callers call net_drop_ns() instead.
	* sysfs_exit_ns() is gone, along with a large part of callchain
leading to it; now that the references stored in ->ns[...] stay valid we
do not need to hunt them down and replace them with NULL.  That fixes
problems in sysfs_lookup() and sysfs_readdir(), along with getting rid
of sb->s_instances abuse.

	Note that struct net *shutdown* logics has not changed - net_cleanup()
is called exactly when it used to be called.  The only thing postponed by
having a sysfs instance refering to that struct net is actual freeing of
memory occupied by struct net.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 19 insertions, 16 deletions

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 11b98bc2aa8f..33d2a1fba131 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1179,9 +1179,14 @@ static void remove_queue_kobjects(struct net_device *net)
 #endif
 }
 
-static const void *net_current_ns(void)
+static void *net_grab_current_ns(void)
 {
-        return current->nsproxy->net_ns;
+        struct net *ns = current->nsproxy->net_ns;
+#ifdef CONFIG_NET_NS
+        if (ns)
+                atomic_inc(&ns->passive);
+#endif
+        return ns;
 }
 
 static const void *net_initial_ns(void)
@@ -1196,22 +1201,13 @@ static const void *net_netlink_ns(struct sock *sk)
 
 struct kobj_ns_type_operations net_ns_type_operations = {
         .type = KOBJ_NS_TYPE_NET,
-        .current_ns = net_current_ns,
+        .grab_current_ns = net_grab_current_ns,
         .netlink_ns = net_netlink_ns,
         .initial_ns = net_initial_ns,
+        .drop_ns = net_drop_ns,
 };
 EXPORT_SYMBOL_GPL(net_ns_type_operations);
 
-static void net_kobj_ns_exit(struct net *net)
-{
-        kobj_ns_exit(KOBJ_NS_TYPE_NET, net);
-}
-
-static struct pernet_operations kobj_net_ops = {
-        .exit = net_kobj_ns_exit,
-};
-
-
 #ifdef CONFIG_HOTPLUG
 static int netdev_uevent(struct device *d, struct kobj_uevent_env *env)
 {
@@ -1339,6 +1335,5 @@ EXPORT_SYMBOL(netdev_class_remove_file);
 int netdev_kobject_init(void)
 {
         kobj_ns_type_register(&net_ns_type_operations);
-        register_pernet_subsys(&kobj_net_ops);
         return class_register(&net_class);
 }
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 6c6b86d0da15..cdcbc3cb00a9 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -128,6 +128,7 @@ static __net_init int setup_net(struct net *net)
         LIST_HEAD(net_exit_list);
 
         atomic_set(&net->count, 1);
+        atomic_set(&net->passive, 1);
 
 #ifdef NETNS_REFCNT_DEBUG
         atomic_set(&net->use_count, 0);
@@ -210,6 +211,13 @@ static void net_free(struct net *net)
         kmem_cache_free(net_cachep, net);
 }
 
+void net_drop_ns(void *p)
+{
+        struct net *ns = p;
+        if (ns && atomic_dec_and_test(&ns->passive))
+                net_free(ns);
+}
+
 struct net *copy_net_ns(unsigned long flags, struct net *old_net)
 {
         struct net *net;
@@ -230,7 +238,7 @@ struct net *copy_net_ns(unsigned long flags, struct net *old_net)
         }
         mutex_unlock(&net_mutex);
         if (rv < 0) {
-                net_free(net);
+                net_drop_ns(net);
                 return ERR_PTR(rv);
         }
         return net;
@@ -286,7 +294,7 @@ static void cleanup_net(struct work_struct *work)
         /* Finally it is safe to free my network namespace structure */
         list_for_each_entry_safe(net, tmp, &net_exit_list, exit_list) {
                 list_del_init(&net->exit_list);
-                net_free(net);
+                net_drop_ns(net);
         }
 }
 static DECLARE_WORK(net_cleanup_work, cleanup_net);