From 94d250fae48e6f873d8362308f5c4d02cd1b1fd2 Mon Sep 17 00:00:00 2001
From: Bernd Eckstein <3erndeckstein@gmail.com>
Date: Mon, 20 May 2019 17:31:09 +0200
Subject: [PATCH] usbnet: ipheth: fix racing condition
Git-commit: 94d250fae48e6f873d8362308f5c4d02cd1b1fd2
Patch-mainline: v5.2-rc2
References: bsc#1051510

Fix a racing condition in ipheth.c that can lead to slow performance.

Bug: In ipheth_tx(), netif_wake_queue() may be called on the callback
ipheth_sndbulk_callback(), _before_ netif_stop_queue() is called.
When this happens, the queue is stopped longer than it needs to be,
thus reducing network performance.

Fix: Move netif_stop_queue() in front of usb_submit_urb(). Now the order
is always correct. In case, usb_submit_urb() fails, the queue is woken up
again as callback will not fire.

Testing: This racing condition is usually not noticeable, as it has to
occur very frequently to slowdown the network. The callback from the USB
is usually triggered slow enough, so the situation does not appear.
However, on a Ubuntu Linux on VMWare Workstation, running on Windows 10,
the we loose the race quite often and the following speedup can be noticed:

Without this patch: Download:  4.10 Mbit/s, Upload:  4.01 Mbit/s
With this patch:    Download: 36.23 Mbit/s, Upload: 17.61 Mbit/s

Signed-off-by: Oliver Zweigle <Oliver.Zweigle@faro.com>
Signed-off-by: Bernd Eckstein <3ernd.Eckstein@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/net/usb/ipheth.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/ipheth.c b/drivers/net/usb/ipheth.c
index c247aed2dceb..8c01fbf68a89 100644
--- a/drivers/net/usb/ipheth.c
+++ b/drivers/net/usb/ipheth.c
@@ -383,17 +383,18 @@ static int ipheth_tx(struct sk_buff *skb, struct net_device *net)
 			  dev);
 	dev->tx_urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
 
+	netif_stop_queue(net);
 	retval = usb_submit_urb(dev->tx_urb, GFP_ATOMIC);
 	if (retval) {
 		dev_err(&dev->intf->dev, "%s: usb_submit_urb: %d\n",
 			__func__, retval);
 		dev->net->stats.tx_errors++;
 		dev_kfree_skb_any(skb);
+		netif_wake_queue(net);
 	} else {
 		dev->net->stats.tx_packets++;
 		dev->net->stats.tx_bytes += skb->len;
 		dev_consume_skb_any(skb);
-		netif_stop_queue(net);
 	}
 
 	return NETDEV_TX_OK;
-- 
2.16.4