queue-4.9/usbnet-ipheth-fix-racing-condition.patch

   1 From 3d109e979f72e05b3022f3a1747d9bcb079b908d Mon Sep 17 00:00:00 2001
   2 From: Bernd Eckstein <3erndeckstein@gmail.com>
   3 Date: Mon, 20 May 2019 17:31:09 +0200
   4 Subject: usbnet: ipheth: fix racing condition
   5
   6 [ Upstream commit 94d250fae48e6f873d8362308f5c4d02cd1b1fd2 ]
   7
   8 Fix a racing condition in ipheth.c that can lead to slow performance.
   9
  10 Bug: In ipheth_tx(), netif_wake_queue() may be called on the callback
  11 ipheth_sndbulk_callback(), _before_ netif_stop_queue() is called.
  12 When this happens, the queue is stopped longer than it needs to be,
  13 thus reducing network performance.
  14
  15 Fix: Move netif_stop_queue() in front of usb_submit_urb(). Now the order
  16 is always correct. In case, usb_submit_urb() fails, the queue is woken up
  17 again as callback will not fire.
  18
  19 Testing: This racing condition is usually not noticeable, as it has to
  20 occur very frequently to slowdown the network. The callback from the USB
  21 is usually triggered slow enough, so the situation does not appear.
  22 However, on a Ubuntu Linux on VMWare Workstation, running on Windows 10,
  23 the we loose the race quite often and the following speedup can be noticed:
  24
  25 Without this patch: Download:  4.10 Mbit/s, Upload:  4.01 Mbit/s
  26 With this patch:    Download: 36.23 Mbit/s, Upload: 17.61 Mbit/s
  27
  28 Signed-off-by: Oliver Zweigle <Oliver.Zweigle@faro.com>
  29 Signed-off-by: Bernd Eckstein <3ernd.Eckstein@gmail.com>
  30 Signed-off-by: David S. Miller <davem@davemloft.net>
  31 Signed-off-by: Sasha Levin <sashal@kernel.org>
  32 ---
  33  drivers/net/usb/ipheth.c | 3 ++-
  34  1 file changed, 2 insertions(+), 1 deletion(-)
  35
  36 diff --git a/drivers/net/usb/ipheth.c b/drivers/net/usb/ipheth.c
  37 index 01f95d192d25..2b16a5fed9de 100644
  38 --- a/drivers/net/usb/ipheth.c
  39 +++ b/drivers/net/usb/ipheth.c
  40 @@ -437,17 +437,18 @@ static int ipheth_tx(struct sk_buff *skb, struct net_device *net)
  41                           dev);
  42         dev->tx_urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
  43
  44 +       netif_stop_queue(net);
  45         retval = usb_submit_urb(dev->tx_urb, GFP_ATOMIC);
  46         if (retval) {
  47                 dev_err(&dev->intf->dev, "%s: usb_submit_urb: %d\n",
  48                         __func__, retval);
  49                 dev->net->stats.tx_errors++;
  50                 dev_kfree_skb_any(skb);
  51 +               netif_wake_queue(net);
  52         } else {
  53                 dev->net->stats.tx_packets++;
  54                 dev->net->stats.tx_bytes += skb->len;
  55                 dev_consume_skb_any(skb);
  56 -               netif_stop_queue(net);
  57         }
  58
  59         return NETDEV_TX_OK;
  60 --
  61 2.20.1
  62