On Thu, 24 May 2018 09:55:13 -0700
Sridhar Samudrala [off-list ref] wrote:

+	spin_lock(&failover_lock);

Since register is not in fast path, this should be a mutex?

+int failover_slave_unregister(struct net_device *slave_dev)
+{
+	struct net_device *failover_dev;
+	struct failover_ops *fops;
+
+	if (!netif_is_failover_slave(slave_dev))
+		goto done;
+
+	ASSERT_RTNL();
+
+	failover_dev = failover_get_bymac(slave_dev->perm_addr, &fops);
+	if (!failover_dev)
+		goto done;

Since the slave device must have a master device set already, why not use
that instead of searching by MAC address on unregister or link change.