ixgb: remove ndo_poll_controller

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.

ixgb uses NAPI for TX completions, so we better let core
networking stack call the napi->poll() to avoid the capture.

This also removes a problematic use of disable_irq() in
a context it is forbidden, as explained in commit
af3e0fcf7887 ("8139too: Use disable_irq_nosync() in
rtl8139_poll_controller()")

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/intel/ixgb/ixgb_main.c

@@ -81,11 +81,6 @@ static int ixgb_vlan_rx_kill_vid(struct net_device *netdev,
 				 __be16 proto, u16 vid);
 static void ixgb_restore_vlan(struct ixgb_adapter *adapter);
 
-#ifdef CONFIG_NET_POLL_CONTROLLER
-/* for netdump / net console */
-static void ixgb_netpoll(struct net_device *dev);
-#endif
-
 static pci_ers_result_t ixgb_io_error_detected (struct pci_dev *pdev,
                              enum pci_channel_state state);
 static pci_ers_result_t ixgb_io_slot_reset (struct pci_dev *pdev);
@@ -348,9 +343,6 @@ static const struct net_device_ops ixgb_netdev_ops = {
 	.ndo_tx_timeout		= ixgb_tx_timeout,
 	.ndo_vlan_rx_add_vid	= ixgb_vlan_rx_add_vid,
 	.ndo_vlan_rx_kill_vid	= ixgb_vlan_rx_kill_vid,
-#ifdef CONFIG_NET_POLL_CONTROLLER
-	.ndo_poll_controller	= ixgb_netpoll,
-#endif
 	.ndo_fix_features       = ixgb_fix_features,
 	.ndo_set_features       = ixgb_set_features,
 };
@@ -2195,23 +2187,6 @@ ixgb_restore_vlan(struct ixgb_adapter *adapter)
 		ixgb_vlan_rx_add_vid(adapter->netdev, htons(ETH_P_8021Q), vid);
 }
 
-#ifdef CONFIG_NET_POLL_CONTROLLER
-/*
- * Polling 'interrupt' - used by things like netconsole to send skbs
- * without having to re-enable interrupts. It's not called while
- * the interrupt routine is executing.
- */
-
-static void ixgb_netpoll(struct net_device *dev)
-{
-	struct ixgb_adapter *adapter = netdev_priv(dev);
-
-	disable_irq(adapter->pdev->irq);
-	ixgb_intr(adapter->pdev->irq, dev);
-	enable_irq(adapter->pdev->irq);
-}
-#endif
-
 /**
  * ixgb_io_error_detected - called when PCI error is detected
  * @pdev:    pointer to pci device with error