[PATCH v4 net-next 01/15] net: add exit_batch_rtnl() method

[Eric Dumazet <edumazet@google.com>]

Many (struct pernet_operations)->exit_batch() methods have
to acquire rtnl.

In presence of rtnl mutex pressure, this makes cleanup_net()
very slow.

This patch adds a new exit_batch_rtnl() method to reduce
number of rtnl acquisitions from cleanup_net().

exit_batch_rtnl() handlers are called while rtnl is locked,
and devices to be killed can be queued in a list provided
as their second argument.

A single unregister_netdevice_many() is called right
before rtnl is released.

exit_batch_rtnl() handlers are called before ->exit() and
->exit_batch() handlers.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/net/net_namespace.h |  3 +++
 net/core/net_namespace.c    | 31 ++++++++++++++++++++++++++++++-
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index cd0c2eedbb5e9ddcbd5e0a37e2eb7e0cf57495d5..20c34bd7a07783a9a13696fd74b41eff1ff860a8 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -448,6 +448,9 @@ struct pernet_operations {
 	void (*pre_exit)(struct net *net);
 	void (*exit)(struct net *net);
 	void (*exit_batch)(struct list_head *net_exit_list);
+	/* Following method is called with RTNL held. */
+	void (*exit_batch_rtnl)(struct list_head *net_exit_list,
+				struct list_head *dev_kill_list);
 	unsigned int *id;
 	size_t size;
 };
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 72799533426b6162256d7c4eef355af96c66e844..233ec0cdd0111d5ca21c6f8a66f4c1f3fbc4657b 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -318,8 +318,9 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
 {
 	/* Must be called with pernet_ops_rwsem held */
 	const struct pernet_operations *ops, *saved_ops;
-	int error = 0;
 	LIST_HEAD(net_exit_list);
+	LIST_HEAD(dev_kill_list);
+	int error = 0;
 
 	refcount_set(&net->ns.count, 1);
 	ref_tracker_dir_init(&net->refcnt_tracker, 128, "net refcnt");
@@ -357,6 +358,15 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
 
 	synchronize_rcu();
 
+	ops = saved_ops;
+	rtnl_lock();
+	list_for_each_entry_continue_reverse(ops, &pernet_list, list) {
+		if (ops->exit_batch_rtnl)
+			ops->exit_batch_rtnl(&net_exit_list, &dev_kill_list);
+	}
+	unregister_netdevice_many(&dev_kill_list);
+	rtnl_unlock();
+
 	ops = saved_ops;
 	list_for_each_entry_continue_reverse(ops, &pernet_list, list)
 		ops_exit_list(ops, &net_exit_list);
@@ -573,6 +583,7 @@ static void cleanup_net(struct work_struct *work)
 	struct net *net, *tmp, *last;
 	struct llist_node *net_kill_list;
 	LIST_HEAD(net_exit_list);
+	LIST_HEAD(dev_kill_list);
 
 	/* Atomically snapshot the list of namespaces to cleanup */
 	net_kill_list = llist_del_all(&cleanup_list);
@@ -613,6 +624,14 @@ static void cleanup_net(struct work_struct *work)
 	 */
 	synchronize_rcu();
 
+	rtnl_lock();
+	list_for_each_entry_reverse(ops, &pernet_list, list) {
+		if (ops->exit_batch_rtnl)
+			ops->exit_batch_rtnl(&net_exit_list, &dev_kill_list);
+	}
+	unregister_netdevice_many(&dev_kill_list);
+	rtnl_unlock();
+
 	/* Run all of the network namespace exit methods */
 	list_for_each_entry_reverse(ops, &pernet_list, list)
 		ops_exit_list(ops, &net_exit_list);
@@ -1193,7 +1212,17 @@ static void free_exit_list(struct pernet_operations *ops, struct list_head *net_
 {
 	ops_pre_exit_list(ops, net_exit_list);
 	synchronize_rcu();
+
+	if (ops->exit_batch_rtnl) {
+		LIST_HEAD(dev_kill_list);
+
+		rtnl_lock();
+		ops->exit_batch_rtnl(net_exit_list, &dev_kill_list);
+		unregister_netdevice_many(&dev_kill_list);
+		rtnl_unlock();
+	}
 	ops_exit_list(ops, net_exit_list);
+
 	ops_free_list(ops, net_exit_list);
 }
 
-- 
2.43.0.594.gd9cf4e227d-goog