hv_netvsc: remove ndo_poll_controller

Similar to other patches from ERic.

As diagnosed by Song Liu, ndo_poll_controller() can
be very dangerous on loaded hosts, since the cpu
calling ndo_poll_controller() might steal all NAPI
contexts (for all RX/TX queues of the NIC). This capture
can last for unlimited amount of time, since one
cpu is generally not able to drain all the queues under load.

In netvsc driver it uses NAPI for TX completions. The default
poll_napi will do this for us now and avoid the capture.
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Eric Dumazet <edumazet@google.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/netvsc_drv.c

@@ -1565,26 +1565,6 @@ netvsc_set_rxnfc(struct net_device *ndev, struct ethtool_rxnfc *info)
 	return -EOPNOTSUPP;
 }
 
-#ifdef CONFIG_NET_POLL_CONTROLLER
-static void netvsc_poll_controller(struct net_device *dev)
-{
-	struct net_device_context *ndc = netdev_priv(dev);
-	struct netvsc_device *ndev;
-	int i;
-
-	rcu_read_lock();
-	ndev = rcu_dereference(ndc->nvdev);
-	if (ndev) {
-		for (i = 0; i < ndev->num_chn; i++) {
-			struct netvsc_channel *nvchan = &ndev->chan_table[i];
-
-			napi_schedule(&nvchan->napi);
-		}
-	}
-	rcu_read_unlock();
-}
-#endif
-
 static u32 netvsc_get_rxfh_key_size(struct net_device *dev)
 {
 	return NETVSC_HASH_KEYLEN;
@@ -1812,9 +1792,6 @@ static const struct net_device_ops device_ops = {
 	.ndo_set_mac_address =		netvsc_set_mac_addr,
 	.ndo_select_queue =		netvsc_select_queue,
 	.ndo_get_stats64 =		netvsc_get_stats64,
-#ifdef CONFIG_NET_POLL_CONTROLLER
-	.ndo_poll_controller =		netvsc_poll_controller,
-#endif
 };
 
 /*