net: make dev_unreg_count global

We can use a global dev_unreg_count counter instead
of a per netns one.

As a bonus we can factorize the changes done on it
for bulk device removals.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: edumazet

include/linux/rtnetlink.h

@@ -47,6 +47,7 @@ extern int rtnl_lock_killable(void);
 extern bool refcount_dec_and_rtnl_lock(refcount_t *r);
 
 extern wait_queue_head_t netdev_unregistering_wq;
+extern atomic_t dev_unreg_count;
 extern struct rw_semaphore pernet_ops_rwsem;
 extern struct rw_semaphore net_rwsem;
 

include/net/net_namespace.h

@@ -67,8 +67,6 @@ struct net {
 						 */
 	spinlock_t		rules_mod_lock;
 
-	atomic_t		dev_unreg_count;
-
 	unsigned int		dev_base_seq;	/* protected by rtnl_mutex */
 	u32			ifindex;
 

net/core/dev.c

@@ -9698,11 +9698,11 @@ static void dev_index_release(struct net *net, int ifindex)
 /* Delayed registration/unregisteration */
 LIST_HEAD(net_todo_list);
 DECLARE_WAIT_QUEUE_HEAD(netdev_unregistering_wq);
+atomic_t dev_unreg_count = ATOMIC_INIT(0);
 
 static void net_set_todo(struct net_device *dev)
 {
 	list_add_tail(&dev->todo_list, &net_todo_list);
-	atomic_inc(&dev_net(dev)->dev_unreg_count);
 }
 
 static netdev_features_t netdev_sync_upper_features(struct net_device *lower,
@@ -10529,6 +10529,7 @@ void netdev_run_todo(void)
 {
 	struct net_device *dev, *tmp;
 	struct list_head list;
+	int cnt;
 #ifdef CONFIG_LOCKDEP
 	struct list_head unlink_list;
 
@@ -10565,6 +10566,7 @@ void netdev_run_todo(void)
 		linkwatch_sync_dev(dev);
 	}
 
+	cnt = 0;
 	while (!list_empty(&list)) {
 		dev = netdev_wait_allrefs_any(&list);
 		list_del(&dev->todo_list);
@@ -10582,12 +10584,13 @@ void netdev_run_todo(void)
 		if (dev->needs_free_netdev)
 			free_netdev(dev);
 
-		if (atomic_dec_and_test(&dev_net(dev)->dev_unreg_count))
-			wake_up(&netdev_unregistering_wq);
+		cnt++;
 
 		/* Free network device */
 		kobject_put(&dev->dev.kobj);
 	}
+	if (cnt && atomic_sub_and_test(cnt, &dev_unreg_count))
+		wake_up(&netdev_unregistering_wq);
 }
 
 /* Convert net_device_stats to rtnl_link_stats64. rtnl_link_stats64 has
@@ -11034,6 +11037,7 @@ void unregister_netdevice_many_notify(struct list_head *head,
 {
 	struct net_device *dev, *tmp;
 	LIST_HEAD(close_head);
+	int cnt = 0;
 
 	BUG_ON(dev_boot_phase);
 	ASSERT_RTNL();
@@ -11130,7 +11134,9 @@ void unregister_netdevice_many_notify(struct list_head *head,
 	list_for_each_entry(dev, head, unreg_list) {
 		netdev_put(dev, &dev->dev_registered_tracker);
 		net_set_todo(dev);
+		cnt++;
 	}
+	atomic_add(cnt, &dev_unreg_count);
 
 	list_del(head);
 }

net/core/rtnetlink.c

@@ -483,24 +483,15 @@ EXPORT_SYMBOL_GPL(__rtnl_link_unregister);
  */
 static void rtnl_lock_unregistering_all(void)
 {
-	struct net *net;
-	bool unregistering;
 	DEFINE_WAIT_FUNC(wait, woken_wake_function);
 
 	add_wait_queue(&netdev_unregistering_wq, &wait);
 	for (;;) {
-		unregistering = false;
 		rtnl_lock();
 		/* We held write locked pernet_ops_rwsem, and parallel
 		 * setup_net() and cleanup_net() are not possible.
 		 */
-		for_each_net(net) {
-			if (atomic_read(&net->dev_unreg_count) > 0) {
-				unregistering = true;
-				break;
-			}
-		}
-		if (!unregistering)
+		if (!atomic_read(&dev_unreg_count))
 			break;
 		__rtnl_unlock();