netdev - [PATCH net 05/11] virtio_net: remove ndo_poll

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Date:   Thu, 27 Sep 2018 09:31:55 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Michael Chan <michael.chan@...adcom.com>,
        Aviad Krawczyk <aviad.krawczyk@...wei.com>,
        Song Liu <songliubraving@...com>,
        Douglas Miller <dougmill@...ux.vnet.ibm.com>,
        Yisen Zhuang <yisen.zhuang@...wei.com>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Harish Patil <harish.patil@...ium.com>,
        Manish Chopra <manish.chopra@...ium.com>,
        Netanel Belgazal <netanel@...zon.com>,
        Solarflare linux maintainers <linux-net-drivers@...arflare.com>,
        Thomas Falcon <tlfalcon@...ux.vnet.ibm.com>
Subject: [PATCH net 05/11] virtio_net: 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.

virto_net 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@...gle.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Jason Wang <jasowang@...hat.com>
---
 drivers/net/virtio_net.c | 14 --------------
 1 file changed, 14 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 76592090522607a4bdf5422b1d49ec99c6fd68ac..dab504ec5e502be401cbfe9a8e3f0f572c0220ba 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1699,17 +1699,6 @@ static void virtnet_stats(struct net_device *dev,
 	tot->rx_frame_errors = dev->stats.rx_frame_errors;
 }
 
-#ifdef CONFIG_NET_POLL_CONTROLLER
-static void virtnet_netpoll(struct net_device *dev)
-{
-	struct virtnet_info *vi = netdev_priv(dev);
-	int i;
-
-	for (i = 0; i < vi->curr_queue_pairs; i++)
-		napi_schedule(&vi->rq[i].napi);
-}
-#endif
-
 static void virtnet_ack_link_announce(struct virtnet_info *vi)
 {
 	rtnl_lock();
@@ -2447,9 +2436,6 @@ static const struct net_device_ops virtnet_netdev = {
 	.ndo_get_stats64     = virtnet_stats,
 	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
 	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
-#ifdef CONFIG_NET_POLL_CONTROLLER
-	.ndo_poll_controller = virtnet_netpoll,
-#endif
 	.ndo_bpf		= virtnet_xdp,
 	.ndo_xdp_xmit		= virtnet_xdp_xmit,
 	.ndo_features_check	= passthru_features_check,
-- 
2.19.0.605.g01d371f741-goog