Merge branch 'netpoll-avoid-capture-effects-for-NAPI-drivers'

Eric Dumazet says:

====================
netpoll: avoid capture effects for NAPI drivers

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, showing one ksoftirqd eating all cycles
can last for unlimited amount of time, since one
cpu is generally not able to drain all the queues under load.

It seems that all networking drivers that do use NAPI
for their TX completions, should not provide a ndo_poll_controller() :

Most NAPI drivers have netpoll support already handled
in core networking stack, since netpoll_poll_dev()
uses poll_napi(dev) to iterate through registered
NAPI contexts for a device.

This patch series take care of the first round, we will
handle other drivers in future rounds.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 0 insertions, 43 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index ebd07ad82431..e2648b5a3861 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1153,43 +1153,6 @@ static netdev_features_t tun_net_fix_features(struct net_device *dev,
 
 	return (features & tun->set_features) | (features & ~TUN_USER_FEATURES);
 }
-#ifdef CONFIG_NET_POLL_CONTROLLER
-static void tun_poll_controller(struct net_device *dev)
-{
-	/*
-	 * Tun only receives frames when:
-	 * 1) the char device endpoint gets data from user space
-	 * 2) the tun socket gets a sendmsg call from user space
-	 * If NAPI is not enabled, since both of those are synchronous
-	 * operations, we are guaranteed never to have pending data when we poll
-	 * for it so there is nothing to do here but return.
-	 * We need this though so netpoll recognizes us as an interface that
-	 * supports polling, which enables bridge devices in virt setups to
-	 * still use netconsole
-	 * If NAPI is enabled, however, we need to schedule polling for all
-	 * queues unless we are using napi_gro_frags(), which we call in
-	 * process context and not in NAPI context.
-	 */
-	struct tun_struct *tun = netdev_priv(dev);
-
-	if (tun->flags & IFF_NAPI) {
-		struct tun_file *tfile;
-		int i;
-
-		if (tun_napi_frags_enabled(tun))
-			return;
-
-		rcu_read_lock();
-		for (i = 0; i < tun->numqueues; i++) {
-			tfile = rcu_dereference(tun->tfiles[i]);
-			if (tfile->napi_enabled)
-				napi_schedule(&tfile->napi);
-		}
-		rcu_read_unlock();
-	}
-	return;
-}
-#endif
 
 static void tun_set_headroom(struct net_device *dev, int new_hr)
 {
@@ -1283,9 +1246,6 @@ static const struct net_device_ops tun_netdev_ops = {
 	.ndo_start_xmit		= tun_net_xmit,
 	.ndo_fix_features	= tun_net_fix_features,
 	.ndo_select_queue	= tun_select_queue,
-#ifdef CONFIG_NET_POLL_CONTROLLER
-	.ndo_poll_controller	= tun_poll_controller,
-#endif
 	.ndo_set_rx_headroom	= tun_set_headroom,
 	.ndo_get_stats64	= tun_net_get_stats64,
 };
@@ -1365,9 +1325,6 @@ static const struct net_device_ops tap_netdev_ops = {
 	.ndo_set_mac_address	= eth_mac_addr,
 	.ndo_validate_addr	= eth_validate_addr,
 	.ndo_select_queue	= tun_select_queue,
-#ifdef CONFIG_NET_POLL_CONTROLLER
-	.ndo_poll_controller	= tun_poll_controller,
-#endif
 	.ndo_features_check	= passthru_features_check,
 	.ndo_set_rx_headroom	= tun_set_headroom,
 	.ndo_get_stats64	= tun_net_get_stats64,