sysctl: Implement retire_sysctl_set

This adds a small helper retire_sysctl_set to remove the intimate knowledge about
the how a sysctl_set is implemented from net/sysct_net.c
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>

fs/proc/proc_sysctl.c

@@ -1080,6 +1080,10 @@ void setup_sysctl_set(struct ctl_table_set *p,
 	p->is_seen = is_seen;
 }
 
+void retire_sysctl_set(struct ctl_table_set *set)
+{
+	WARN_ON(!list_empty(&set->list));
+}
 
 int __init proc_sys_init(void)
 {

include/linux/sysctl.h

@@ -1072,6 +1072,7 @@ void proc_sys_poll_notify(struct ctl_table_poll *poll);
 extern void setup_sysctl_set(struct ctl_table_set *p,
 	struct ctl_table_set *parent,
 	int (*is_seen)(struct ctl_table_set *));
+extern void retire_sysctl_set(struct ctl_table_set *set);
 
 void register_sysctl_root(struct ctl_table_root *root);
 struct ctl_table_header *__register_sysctl_paths(

net/sysctl_net.c

@@ -82,7 +82,7 @@ static int __net_init sysctl_net_init(struct net *net)
 
 static void __net_exit sysctl_net_exit(struct net *net)
 {
-	WARN_ON(!list_empty(&net->sysctls.list));
+	retire_sysctl_set(&net->sysctls);
 }
 
 static struct pernet_operations sysctl_pernet_ops = {