geneve: move debug check after netdev unregister

The debug check must be done after unregister_netdevice_many() call --
the list_del() for this is done inside .ndo_stop.

Fixes: 2843a25348 ("geneve: speedup geneve tunnels dismantle")
Reported-and-tested-by: <syzbot+68a8ed58e3d17c700de5@syzkaller.appspotmail.com>
Cc: Haishuang Yan <yanhaishuang@cmss.chinamobile.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/geneve.c

@@ -1845,8 +1845,6 @@ static void geneve_destroy_tunnels(struct net *net, struct list_head *head)
 		if (!net_eq(dev_net(geneve->dev), net))
 			unregister_netdevice_queue(geneve->dev, head);
 	}
-
-	WARN_ON_ONCE(!list_empty(&gn->sock_list));
 }
 
 static void __net_exit geneve_exit_batch_net(struct list_head *net_list)
@@ -1861,6 +1859,12 @@ static void __net_exit geneve_exit_batch_net(struct list_head *net_list)
 	/* unregister the devices gathered above */
 	unregister_netdevice_many(&list);
 	rtnl_unlock();
+
+	list_for_each_entry(net, net_list, exit_list) {
+		const struct geneve_net *gn = net_generic(net, geneve_net_id);
+
+		WARN_ON_ONCE(!list_empty(&gn->sock_list));
+	}
 }
 
 static struct pernet_operations geneve_net_ops = {