hv_netvsc: fix locking for rx_mode

The rx_mode operation handler is different than other callbacks
in that is not always called with rtnl held. Therefore use
RCU to ensure that references are valid.

Fixes: bee9d41 ("hv_netvsc: propagate rx filters to VF")
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/netvsc_drv.c

@@ -89,15 +89,20 @@ static void netvsc_change_rx_flags(struct net_device *net, int change)
 static void netvsc_set_rx_mode(struct net_device *net)
 {
 	struct net_device_context *ndev_ctx = netdev_priv(net);
-	struct net_device *vf_netdev = rtnl_dereference(ndev_ctx->vf_netdev);
-	struct netvsc_device *nvdev = rtnl_dereference(ndev_ctx->nvdev);
+	struct net_device *vf_netdev;
+	struct netvsc_device *nvdev;
 
+	rcu_read_lock();
+	vf_netdev = rcu_dereference(ndev_ctx->vf_netdev);
 	if (vf_netdev) {
 		dev_uc_sync(vf_netdev, net);
 		dev_mc_sync(vf_netdev, net);
 	}
 
-	rndis_filter_update(nvdev);
+	nvdev = rcu_dereference(ndev_ctx->nvdev);
+	if (nvdev)
+		rndis_filter_update(nvdev);
+	rcu_read_unlock();
 }
 
 static int netvsc_open(struct net_device *net)