Re: [PATCH net-next v7 03/25] net: introduce OpenVPN Data Channel Offload (ovpn)

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Antonio Quartulli <antonio@openvpn.net>
Date: Tue, 17 Sep 2024 03:07:12 +0200
> +/* we register with rtnl to let core know that ovpn is a virtual driver and
> + * therefore ifaces should be destroyed when exiting a netns
> + */
> +static struct rtnl_link_ops ovpn_link_ops = {
> +};

This looks like abusing rtnl_link_ops.

Instead of a hack to rely on default_device_exit_batch()
and rtnl_link_unregister(), this should be implemented as
struct pernet_operations.exit_batch_rtnl().

Then, the patch 2 is not needed, which is confusing for
all other rtnl_link_ops users.

If we want to avoid extra RTNL in default_device_exit_batch(),
I can post this patch after merge window.

---8<---
diff --git a/net/core/dev.c b/net/core/dev.c
index 1e740faf9e78..eacf6f5a6ace 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -11916,7 +11916,8 @@ static void __net_exit default_device_exit_net(struct net *net)
 	}
 }
 
-static void __net_exit default_device_exit_batch(struct list_head *net_list)
+void __net_exit default_device_exit_batch(struct list_head *net_list,
+					  struct list_head *dev_kill_list)
 {
 	/* At exit all network devices most be removed from a network
 	 * namespace.  Do this in the reverse order of registration.
@@ -11925,9 +11926,7 @@ static void __net_exit default_device_exit_batch(struct list_head *net_list)
 	 */
 	struct net_device *dev;
 	struct net *net;
-	LIST_HEAD(dev_kill_list);
 
-	rtnl_lock();
 	list_for_each_entry(net, net_list, exit_list) {
 		default_device_exit_net(net);
 		cond_resched();
@@ -11936,19 +11935,13 @@ static void __net_exit default_device_exit_batch(struct list_head *net_list)
 	list_for_each_entry(net, net_list, exit_list) {
 		for_each_netdev_reverse(net, dev) {
 			if (dev->rtnl_link_ops && dev->rtnl_link_ops->dellink)
-				dev->rtnl_link_ops->dellink(dev, &dev_kill_list);
+				dev->rtnl_link_ops->dellink(dev, dev_kill_list);
 			else
-				unregister_netdevice_queue(dev, &dev_kill_list);
+				unregister_netdevice_queue(dev, dev_kill_list);
 		}
 	}
-	unregister_netdevice_many(&dev_kill_list);
-	rtnl_unlock();
 }
 
-static struct pernet_operations __net_initdata default_device_ops = {
-	.exit_batch = default_device_exit_batch,
-};
-
 static void __init net_dev_struct_check(void)
 {
 	/* TX read-mostly hotpath */
@@ -12140,9 +12133,6 @@ static int __init net_dev_init(void)
 	if (register_pernet_device(&loopback_net_ops))
 		goto out;
 
-	if (register_pernet_device(&default_device_ops))
-		goto out;
-
 	open_softirq(NET_TX_SOFTIRQ, net_tx_action);
 	open_softirq(NET_RX_SOFTIRQ, net_rx_action);
 
diff --git a/net/core/dev.h b/net/core/dev.h
index 5654325c5b71..d1feecab9c4a 100644
--- a/net/core/dev.h
+++ b/net/core/dev.h
@@ -99,6 +99,9 @@ void __dev_notify_flags(struct net_device *dev, unsigned int old_flags,
 void unregister_netdevice_many_notify(struct list_head *head,
 				      u32 portid, const struct nlmsghdr *nlh);
 
+void default_device_exit_batch(struct list_head *net_list,
+			       struct list_head *dev_kill_list);
+
 static inline void netif_set_gso_max_size(struct net_device *dev,
 					  unsigned int size)
 {
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 11e4dd4f09ed..0a9bce599d54 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -27,6 +27,8 @@
 #include <net/net_namespace.h>
 #include <net/netns/generic.h>
 
+#include "dev.h"
+
 /*
  *	Our network namespace constructor/destructor lists
  */
@@ -380,6 +382,7 @@ static __net_init int setup_net(struct net *net)
 		if (ops->exit_batch_rtnl)
 			ops->exit_batch_rtnl(&net_exit_list, &dev_kill_list);
 	}
+	default_device_exit_batch(&net_exit_list, &dev_kill_list);
 	unregister_netdevice_many(&dev_kill_list);
 	rtnl_unlock();
 
@@ -618,6 +621,7 @@ static void cleanup_net(struct work_struct *work)
 		if (ops->exit_batch_rtnl)
 			ops->exit_batch_rtnl(&net_exit_list, &dev_kill_list);
 	}
+	default_device_exit_batch(&net_exit_list, &dev_kill_list);
 	unregister_netdevice_many(&dev_kill_list);
 	rtnl_unlock();
 
@@ -1214,6 +1218,7 @@ static void free_exit_list(struct pernet_operations *ops, struct list_head *net_
 
 		rtnl_lock();
 		ops->exit_batch_rtnl(net_exit_list, &dev_kill_list);
+		default_device_exit_batch(net_exit_list, &dev_kill_list);
 		unregister_netdevice_many(&dev_kill_list);
 		rtnl_unlock();
 	}
---8<---