sfc: 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.

sfc uses NAPI for TX completions, so we better let core
networking stack call the napi->poll() to avoid the capture.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Cc: Edward Cree <ecree@solarflare.com>
Cc: Bert Kenward <bkenward@solarflare.com>
Cc: Solarflare linux maintainers <linux-net-drivers@solarflare.com>
Acked-By: NBert Kenward <bkenward@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/efx.c

@@ -2206,29 +2206,6 @@ static void efx_fini_napi(struct efx_nic *efx)
 		efx_fini_napi_channel(channel);
 }
 
-/**************************************************************************
- *
- * Kernel netpoll interface
- *
- *************************************************************************/
-
-#ifdef CONFIG_NET_POLL_CONTROLLER
-
-/* Although in the common case interrupts will be disabled, this is not
- * guaranteed. However, all our work happens inside the NAPI callback,
- * so no locking is required.
- */
-static void efx_netpoll(struct net_device *net_dev)
-{
-	struct efx_nic *efx = netdev_priv(net_dev);
-	struct efx_channel *channel;
-
-	efx_for_each_channel(channel, efx)
-		efx_schedule_channel(channel);
-}
-
-#endif
-
 /**************************************************************************
  *
  * Kernel net device interface
@@ -2509,9 +2486,6 @@ static const struct net_device_ops efx_netdev_ops = {
 #endif
 	.ndo_get_phys_port_id   = efx_get_phys_port_id,
 	.ndo_get_phys_port_name	= efx_get_phys_port_name,
-#ifdef CONFIG_NET_POLL_CONTROLLER
-	.ndo_poll_controller = efx_netpoll,
-#endif
 	.ndo_setup_tc		= efx_setup_tc,
 #ifdef CONFIG_RFS_ACCEL
 	.ndo_rx_flow_steer	= efx_filter_rfs,