net: add uevent socket member

This commit adds struct uevent_sock to struct net. Since struct uevent_sock
records the position of the uevent socket in the uevent socket list we can
trivially remove it from the uevent socket list during cleanup. This speeds
up the old removal codepath.
Note, list_del() will hit __list_del_entry_valid() in its call chain which
will validate that the element is a member of the list. If it isn't it will
take care that the list is not modified.

Signed-off-by: Christian Brauner <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/net_namespace.h

···
 struct sock;
 struct ctl_table_header;
 struct net_generic;
-struct sock;
+struct uevent_sock;
 struct netns_ipvs;
 
 
···
 
 	struct sock 		*rtnl;			/* rtnetlink socket */
 	struct sock		*genl_sock;
+
+	struct uevent_sock	*uevent_sock;		/* uevent socket */
 
 	struct list_head 	dev_base_head;
 	struct hlist_head 	*dev_name_head;

lib/kobject_uevent.c

···
 #ifdef CONFIG_UEVENT_HELPER
 char uevent_helper[UEVENT_HELPER_PATH_LEN] = CONFIG_UEVENT_HELPER_PATH;
 #endif
-#ifdef CONFIG_NET
+
 struct uevent_sock {
 	struct list_head list;
 	struct sock *sk;
 };
+
+#ifdef CONFIG_NET
 static LIST_HEAD(uevent_sock_list);
 #endif
 
···
 		kfree(ue_sk);
 		return -ENODEV;
 	}
+
+	net->uevent_sock = ue_sk;
+
 	mutex_lock(&uevent_sock_mutex);
 	list_add_tail(&ue_sk->list, &uevent_sock_list);
 	mutex_unlock(&uevent_sock_mutex);
···
 
 static void uevent_net_exit(struct net *net)
 {
-	struct uevent_sock *ue_sk;
+	struct uevent_sock *ue_sk = net->uevent_sock;
 
 	mutex_lock(&uevent_sock_mutex);
-	list_for_each_entry(ue_sk, &uevent_sock_list, list) {
-		if (sock_net(ue_sk->sk) == net)
-			goto found;
-	}
-	mutex_unlock(&uevent_sock_mutex);
-	return;
-
-found:
 	list_del(&ue_sk->list);
 	mutex_unlock(&uevent_sock_mutex);