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>

1 files changed, 9 insertions, 14 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);
 }