Merge branch 'netns-init-cleanups' into main

Kuniyuki Iwashima says:

====================
net: Random cleanup for netns initialisation.

patch 1 & 2 suppress unwanted memory allocation for net->gen->ptr[].

patch 3 ~ 6 move part of netns initialisation to prenet_init() that
do not require pernet_ops_rwsem.

v2:
  patch 1 : Removed Fixes: tag
  patch 2 : Use XOR for WARN_ON()

v1: https://lore.kernel.org/netdev/20240729210801.16196-1-kuniyu@amazon.com/
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/net_namespace.h

@@ -451,8 +451,8 @@ struct pernet_operations {
 	/* 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;
+	unsigned int * const id;
+	const size_t size;
 };
 
 /*

net/core/net_namespace.c

@@ -125,7 +125,7 @@ static int ops_init(const struct pernet_operations *ops, struct net *net)
 	int err = -ENOMEM;
 	void *data = NULL;
 
-	if (ops->id && ops->size) {
+	if (ops->id) {
 		data = kzalloc(ops->size, GFP_KERNEL);
 		if (!data)
 			goto out;
@@ -140,7 +140,7 @@ static int ops_init(const struct pernet_operations *ops, struct net *net)
 	if (!err)
 		return 0;
 
-	if (ops->id && ops->size) {
+	if (ops->id) {
 		ng = rcu_dereference_protected(net->gen,
 					       lockdep_is_held(&pernet_ops_rwsem));
 		ng->ptr[*ops->id] = NULL;
@@ -182,7 +182,8 @@ static void ops_free_list(const struct pernet_operations *ops,
 			  struct list_head *net_exit_list)
 {
 	struct net *net;
-	if (ops->size && ops->id) {
+
+	if (ops->id) {
 		list_for_each_entry(net, net_exit_list, exit_list)
 			kfree(net_generic(net, *ops->id));
 	}
@@ -308,16 +309,38 @@ struct net *get_net_ns_by_id(const struct net *net, int id)
 }
 EXPORT_SYMBOL_GPL(get_net_ns_by_id);
 
+static __net_init void preinit_net_sysctl(struct net *net)
+{
+	net->core.sysctl_somaxconn = SOMAXCONN;
+	/* Limits per socket sk_omem_alloc usage.
+	 * TCP zerocopy regular usage needs 128 KB.
+	 */
+	net->core.sysctl_optmem_max = 128 * 1024;
+	net->core.sysctl_txrehash = SOCK_TXREHASH_ENABLED;
+}
+
 /* init code that must occur even if setup_net() is not called. */
-static __net_init void preinit_net(struct net *net)
+static __net_init void preinit_net(struct net *net, struct user_namespace *user_ns)
 {
+	refcount_set(&net->passive, 1);
+	refcount_set(&net->ns.count, 1);
+	ref_tracker_dir_init(&net->refcnt_tracker, 128, "net refcnt");
 	ref_tracker_dir_init(&net->notrefcnt_tracker, 128, "net notrefcnt");
+
+	get_random_bytes(&net->hash_mix, sizeof(u32));
+	net->dev_base_seq = 1;
+	net->user_ns = user_ns;
+
+	idr_init(&net->netns_ids);
+	spin_lock_init(&net->nsid_lock);
+	mutex_init(&net->ipv4.ra_mutex);
+	preinit_net_sysctl(net);
 }
 
 /*
  * setup_net runs the initializers for the network namespace object.
  */
-static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
+static __net_init int setup_net(struct net *net)
 {
 	/* Must be called with pernet_ops_rwsem held */
 	const struct pernet_operations *ops, *saved_ops;
@@ -325,19 +348,9 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
 	LIST_HEAD(dev_kill_list);
 	int error = 0;
 
-	refcount_set(&net->ns.count, 1);
-	ref_tracker_dir_init(&net->refcnt_tracker, 128, "net refcnt");
-
-	refcount_set(&net->passive, 1);
-	get_random_bytes(&net->hash_mix, sizeof(u32));
 	preempt_disable();
 	net->net_cookie = gen_cookie_next(&net_cookie);
 	preempt_enable();
-	net->dev_base_seq = 1;
-	net->user_ns = user_ns;
-	idr_init(&net->netns_ids);
-	spin_lock_init(&net->nsid_lock);
-	mutex_init(&net->ipv4.ra_mutex);
 
 	list_for_each_entry(ops, &pernet_list, list) {
 		error = ops_init(ops, net);
@@ -382,32 +395,6 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
 	goto out;
 }
 
-static int __net_init net_defaults_init_net(struct net *net)
-{
-	net->core.sysctl_somaxconn = SOMAXCONN;
-	/* Limits per socket sk_omem_alloc usage.
-	 * TCP zerocopy regular usage needs 128 KB.
-	 */
-	net->core.sysctl_optmem_max = 128 * 1024;
-	net->core.sysctl_txrehash = SOCK_TXREHASH_ENABLED;
-
-	return 0;
-}
-
-static struct pernet_operations net_defaults_ops = {
-	.init = net_defaults_init_net,
-};
-
-static __init int net_defaults_init(void)
-{
-	if (register_pernet_subsys(&net_defaults_ops))
-		panic("Cannot initialize net default settings");
-
-	return 0;
-}
-
-core_initcall(net_defaults_init);
-
 #ifdef CONFIG_NET_NS
 static struct ucounts *inc_net_namespaces(struct user_namespace *ns)
 {
@@ -496,8 +483,7 @@ struct net *copy_net_ns(unsigned long flags,
 		goto dec_ucounts;
 	}
 
-	preinit_net(net);
-	refcount_set(&net->passive, 1);
+	preinit_net(net, user_ns);
 	net->ucounts = ucounts;
 	get_user_ns(user_ns);
 
@@ -505,7 +491,7 @@ struct net *copy_net_ns(unsigned long flags,
 	if (rv < 0)
 		goto put_userns;
 
-	rv = setup_net(net, user_ns);
+	rv = setup_net(net);
 
 	up_read(&pernet_ops_rwsem);
 
@@ -1199,9 +1185,10 @@ void __init net_ns_init(void)
 #ifdef CONFIG_KEYS
 	init_net.key_domain = &init_net_key_domain;
 #endif
+	preinit_net(&init_net, &init_user_ns);
+
 	down_write(&pernet_ops_rwsem);
-	preinit_net(&init_net);
-	if (setup_net(&init_net, &init_user_ns))
+	if (setup_net(&init_net))
 		panic("Could not setup the initial network namespace");
 
 	init_net_initialized = true;
@@ -1244,7 +1231,7 @@ static int __register_pernet_operations(struct list_head *list,
 	LIST_HEAD(net_exit_list);
 
 	list_add_tail(&ops->list, list);
-	if (ops->init || (ops->id && ops->size)) {
+	if (ops->init || ops->id) {
 		/* We held write locked pernet_ops_rwsem, and parallel
 		 * setup_net() and cleanup_net() are not possible.
 		 */
@@ -1310,6 +1297,9 @@ static int register_pernet_operations(struct list_head *list,
 {
 	int error;
 
+	if (WARN_ON(!!ops->id ^ !!ops->size))
+		return -EINVAL;
+
 	if (ops->id) {
 		error = ida_alloc_min(&net_generic_ids, MIN_PERNET_OPS_ID,
 				GFP_KERNEL);

net/l2tp/l2tp_ppp.c

@@ -1393,8 +1393,6 @@ static int pppol2tp_getsockopt(struct socket *sock, int level, int optname,
  * L2TPv2, we dump only L2TPv2 tunnels and sessions here.
  *****************************************************************************/
 
-static unsigned int pppol2tp_net_id;
-
 #ifdef CONFIG_PROC_FS
 
 struct pppol2tp_seq_data {
@@ -1628,7 +1626,6 @@ static __net_exit void pppol2tp_exit_net(struct net *net)
 static struct pernet_operations pppol2tp_net_ops = {
 	.init = pppol2tp_init_net,
 	.exit = pppol2tp_exit_net,
-	.id   = &pppol2tp_net_id,
 };
 
 /*****************************************************************************