From: Eric Dumazet <edumazet@google.com>
Date: Fri, 21 Sep 2018 15:27:52 -0700
Subject: tun: remove ndo_poll_controller
Patch-mainline: v4.19-rc6
Git-commit: 765cdc209cb89fb81215310a066cd0a3018ffef7
References: bsc#1109837

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.

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

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/net/tun.c |   43 -------------------------------------------
 1 file changed, 43 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1152,43 +1152,6 @@ static netdev_features_t tun_net_fix_fea
 
 	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)
 {
@@ -1282,9 +1245,6 @@ static const struct net_device_ops tun_n
 	.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,
 };
@@ -1364,9 +1324,6 @@ static const struct net_device_ops tap_n
 	.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,