[RFC PATCH net-next 1/3] net: core: introduce netdev_notify_peers_locked

[Lijun Pan <ljp@linux.ibm.com>]

There are some use cases for netdev_notify_peers in the context
when rtnl lock is already held. Introduce lockless version
of netdev_notify_peers call to save the extra code to call
	call_netdevice_notifiers(NETDEV_NOTIFY_PEERS, dev);
	call_netdevice_notifiers(NETDEV_RESEND_IGMP, dev);

Suggested-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Lijun Pan <ljp@linux.ibm.com>
---
 include/linux/netdevice.h |  1 +
 net/core/dev.c            | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 964b494b0e8d..dec16d462672 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -4492,6 +4492,7 @@ int dev_set_promiscuity(struct net_device *dev, int inc);
 int dev_set_allmulti(struct net_device *dev, int inc);
 void netdev_state_change(struct net_device *dev);
 void netdev_notify_peers(struct net_device *dev);
+void netdev_notify_peers_locked(struct net_device *dev);
 void netdev_features_change(struct net_device *dev);
 /* Load a device via the kmod */
 void dev_load(struct net *net, const char *name);
diff --git a/net/core/dev.c b/net/core/dev.c
index 82dc6b48e45f..20c1ab886222 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1488,6 +1488,25 @@ void netdev_notify_peers(struct net_device *dev)
 }
 EXPORT_SYMBOL(netdev_notify_peers);
 
+/**
+ * netdev_notify_peers_locked - notify network peers about existence of @dev,
+ * to be called in the context when rtnl lock is already held.
+ * @dev: network device
+ *
+ * Generate traffic such that interested network peers are aware of
+ * @dev, such as by generating a gratuitous ARP. This may be used when
+ * a device wants to inform the rest of the network about some sort of
+ * reconfiguration such as a failover event or virtual machine
+ * migration.
+ */
+void netdev_notify_peers_locked(struct net_device *dev)
+{
+	ASSERT_RTNL();
+	call_netdevice_notifiers(NETDEV_NOTIFY_PEERS, dev);
+	call_netdevice_notifiers(NETDEV_RESEND_IGMP, dev);
+}
+EXPORT_SYMBOL(netdev_notify_peers_locked);
+
 static int __dev_open(struct net_device *dev, struct netlink_ext_ack *extack)
 {
 	const struct net_device_ops *ops = dev->netdev_ops;
-- 
2.23.0