Merge branch 'net_rwsem-fixes'

Kirill Tkhai says:

====================
net_rwsem fixes

there is wext_netdev_notifier_call()->wireless_nlevent_flush()
netdevice notifier, which takes net_rwsem, so we can't take
net_rwsem in {,un}register_netdevice_notifier().

Since {,un}register_netdevice_notifier() is executed under
pernet_ops_rwsem, net_namespace_list can't change, while we
holding it, so there is no need net_rwsem in these functions [1/2].

The same is in [2/2]. We make callers of __rtnl_link_unregister()
take pernet_ops_rwsem, and close the race with setup_net()
and cleanup_net(), so __rtnl_link_unregister() does not need it.
This also fixes the problem of that __rtnl_link_unregister() does
not see initializing and exiting nets.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dummy.c

@@ -219,6 +219,7 @@ static int __init dummy_init_module(void)
 {
 	int i, err = 0;
 
+	down_write(&pernet_ops_rwsem);
 	rtnl_lock();
 	err = __rtnl_link_register(&dummy_link_ops);
 	if (err < 0)
@@ -233,6 +234,7 @@ static int __init dummy_init_module(void)
 
 out:
 	rtnl_unlock();
+	up_write(&pernet_ops_rwsem);
 
 	return err;
 }

drivers/net/ifb.c

@@ -330,6 +330,7 @@ static int __init ifb_init_module(void)
 {
 	int i, err;
 
+	down_write(&pernet_ops_rwsem);
 	rtnl_lock();
 	err = __rtnl_link_register(&ifb_link_ops);
 	if (err < 0)
@@ -344,6 +345,7 @@ static int __init ifb_init_module(void)
 
 out:
 	rtnl_unlock();
+	up_write(&pernet_ops_rwsem);
 
 	return err;
 }

net/core/dev.c

@@ -1633,7 +1633,6 @@ int register_netdevice_notifier(struct notifier_block *nb)
 		goto unlock;
 	if (dev_boot_phase)
 		goto unlock;
-	down_read(&net_rwsem);
 	for_each_net(net) {
 		for_each_netdev(net, dev) {
 			err = call_netdevice_notifier(nb, NETDEV_REGISTER, dev);
@@ -1647,7 +1646,6 @@ int register_netdevice_notifier(struct notifier_block *nb)
 			call_netdevice_notifier(nb, NETDEV_UP, dev);
 		}
 	}
-	up_read(&net_rwsem);
 
 unlock:
 	rtnl_unlock();
@@ -1671,7 +1669,6 @@ int register_netdevice_notifier(struct notifier_block *nb)
 	}
 
 outroll:
-	up_read(&net_rwsem);
 	raw_notifier_chain_unregister(&netdev_chain, nb);
 	goto unlock;
 }
@@ -1704,7 +1701,6 @@ int unregister_netdevice_notifier(struct notifier_block *nb)
 	if (err)
 		goto unlock;
 
-	down_read(&net_rwsem);
 	for_each_net(net) {
 		for_each_netdev(net, dev) {
 			if (dev->flags & IFF_UP) {
@@ -1715,7 +1711,6 @@ int unregister_netdevice_notifier(struct notifier_block *nb)
 			call_netdevice_notifier(nb, NETDEV_UNREGISTER, dev);
 		}
 	}
-	up_read(&net_rwsem);
 unlock:
 	rtnl_unlock();
 	up_write(&pernet_ops_rwsem);

net/core/net_namespace.c

@@ -51,6 +51,7 @@ static bool init_net_initialized;
  * outside.
  */
 DECLARE_RWSEM(pernet_ops_rwsem);
+EXPORT_SYMBOL_GPL(pernet_ops_rwsem);
 
 #define MIN_PERNET_OPS_ID	\
 	((sizeof(struct net_generic) + sizeof(void *) - 1) / sizeof(void *))

net/core/rtnetlink.c

@@ -412,17 +412,17 @@ static void __rtnl_kill_links(struct net *net, struct rtnl_link_ops *ops)
  * __rtnl_link_unregister - Unregister rtnl_link_ops from rtnetlink.
  * @ops: struct rtnl_link_ops * to unregister
  *
- * The caller must hold the rtnl_mutex.
+ * The caller must hold the rtnl_mutex and guarantee net_namespace_list
+ * integrity (hold pernet_ops_rwsem for writing to close the race
+ * with setup_net() and cleanup_net()).
  */
 void __rtnl_link_unregister(struct rtnl_link_ops *ops)
 {
 	struct net *net;
 
-	down_read(&net_rwsem);
 	for_each_net(net) {
 		__rtnl_kill_links(net, ops);
 	}
-	up_read(&net_rwsem);
 	list_del(&ops->list);
 }
 EXPORT_SYMBOL_GPL(__rtnl_link_unregister);