rtnetlink: Add ASSERT_RTNL_NET() placeholder for netdev notifier.

The global and per-netns netdev notifier depend on RTNL, and its
dependency is not so clear due to nested calls.

Let's add a placeholder to place ASSERT_RTNL_NET() for each event.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/core/Makefile

@@ -45,3 +45,4 @@ obj-$(CONFIG_BPF_SYSCALL) += bpf_sk_storage.o
 obj-$(CONFIG_OF)	+= of_net.o
 obj-$(CONFIG_NET_TEST) += net_test.o
 obj-$(CONFIG_NET_DEVMEM) += devmem.o
+obj-$(CONFIG_DEBUG_NET_SMALL_RTNL) += rtnl_net_debug.o

net/core/rtnl_net_debug.c

@@ -0,0 +1,131 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Copyright Amazon.com Inc. or its affiliates. */
+
+#include <linux/init.h>
+#include <linux/netdevice.h>
+#include <linux/notifier.h>
+#include <linux/rtnetlink.h>
+#include <net/net_namespace.h>
+#include <net/netns/generic.h>
+
+static int rtnl_net_debug_event(struct notifier_block *nb,
+				unsigned long event, void *ptr)
+{
+	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
+	struct net *net = dev_net(dev);
+	enum netdev_cmd cmd = event;
+
+	/* Keep enum and don't add default to trigger -Werror=switch */
+	switch (cmd) {
+	case NETDEV_UP:
+	case NETDEV_DOWN:
+	case NETDEV_REBOOT:
+	case NETDEV_CHANGE:
+	case NETDEV_REGISTER:
+	case NETDEV_UNREGISTER:
+	case NETDEV_CHANGEMTU:
+	case NETDEV_CHANGEADDR:
+	case NETDEV_PRE_CHANGEADDR:
+	case NETDEV_GOING_DOWN:
+	case NETDEV_CHANGENAME:
+	case NETDEV_FEAT_CHANGE:
+	case NETDEV_BONDING_FAILOVER:
+	case NETDEV_PRE_UP:
+	case NETDEV_PRE_TYPE_CHANGE:
+	case NETDEV_POST_TYPE_CHANGE:
+	case NETDEV_POST_INIT:
+	case NETDEV_PRE_UNINIT:
+	case NETDEV_RELEASE:
+	case NETDEV_NOTIFY_PEERS:
+	case NETDEV_JOIN:
+	case NETDEV_CHANGEUPPER:
+	case NETDEV_RESEND_IGMP:
+	case NETDEV_PRECHANGEMTU:
+	case NETDEV_CHANGEINFODATA:
+	case NETDEV_BONDING_INFO:
+	case NETDEV_PRECHANGEUPPER:
+	case NETDEV_CHANGELOWERSTATE:
+	case NETDEV_UDP_TUNNEL_PUSH_INFO:
+	case NETDEV_UDP_TUNNEL_DROP_INFO:
+	case NETDEV_CHANGE_TX_QUEUE_LEN:
+	case NETDEV_CVLAN_FILTER_PUSH_INFO:
+	case NETDEV_CVLAN_FILTER_DROP_INFO:
+	case NETDEV_SVLAN_FILTER_PUSH_INFO:
+	case NETDEV_SVLAN_FILTER_DROP_INFO:
+	case NETDEV_OFFLOAD_XSTATS_ENABLE:
+	case NETDEV_OFFLOAD_XSTATS_DISABLE:
+	case NETDEV_OFFLOAD_XSTATS_REPORT_USED:
+	case NETDEV_OFFLOAD_XSTATS_REPORT_DELTA:
+	case NETDEV_XDP_FEAT_CHANGE:
+		ASSERT_RTNL();
+		break;
+
+	/* Once an event fully supports RTNL_NET, move it here
+	 * and remove "if (0)" below.
+	 *
+	 * case NETDEV_XXX:
+	 *	ASSERT_RTNL_NET(net);
+	 *	break;
+	 */
+	}
+
+	/* Just to avoid unused-variable error for dev and net. */
+	if (0)
+		ASSERT_RTNL_NET(net);
+
+	return NOTIFY_DONE;
+}
+
+static int rtnl_net_debug_net_id;
+
+static int __net_init rtnl_net_debug_net_init(struct net *net)
+{
+	struct notifier_block *nb;
+
+	nb = net_generic(net, rtnl_net_debug_net_id);
+	nb->notifier_call = rtnl_net_debug_event;
+
+	return register_netdevice_notifier_net(net, nb);
+}
+
+static void __net_exit rtnl_net_debug_net_exit(struct net *net)
+{
+	struct notifier_block *nb;
+
+	nb = net_generic(net, rtnl_net_debug_net_id);
+	unregister_netdevice_notifier_net(net, nb);
+}
+
+static struct pernet_operations rtnl_net_debug_net_ops __net_initdata = {
+	.init = rtnl_net_debug_net_init,
+	.exit = rtnl_net_debug_net_exit,
+	.id = &rtnl_net_debug_net_id,
+	.size = sizeof(struct notifier_block),
+};
+
+static struct notifier_block rtnl_net_debug_block = {
+	.notifier_call = rtnl_net_debug_event,
+};
+
+static int __init rtnl_net_debug_init(void)
+{
+	int ret;
+
+	ret = register_pernet_device(&rtnl_net_debug_net_ops);
+	if (ret)
+		return ret;
+
+	ret = register_netdevice_notifier(&rtnl_net_debug_block);
+	if (ret)
+		unregister_pernet_subsys(&rtnl_net_debug_net_ops);
+
+	return ret;
+}
+
+static void __exit rtnl_net_debug_exit(void)
+{
+	unregister_netdevice_notifier(&rtnl_net_debug_block);
+	unregister_pernet_device(&rtnl_net_debug_net_ops);
+}
+
+subsys_initcall(rtnl_net_debug_init);