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[213.61.174.138]) by smtp.gmail.com with ESMTPSA id x1sm11666555wrp.35.2019.05.20.08.31.14 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 20 May 2019 08:31:15 -0700 (PDT) From: Bernd Eckstein <3erndeckstein@gmail.com> X-Google-Original-From: Bernd Eckstein <3ernd.Eckstein@gmail.com> To: davem@davemloft.net Cc: linux@roeck-us.net, linux-usb@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, corsac@corsac.net, Oliver.Zweigle@faro.com, 3ernd.Eckstein@gmail.com Subject: [PATCH] usbnet: ipheth: fix racing condition Date: Mon, 20 May 2019 17:31:09 +0200 Message-Id: <1558366269-17787-1-git-send-email-3ernd.Eckstein@gmail.com> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Signed-off-by: Bernd Eckstein <3ernd.Eckstein@gmail.com> --- 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 c247aed..8c01fbf 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; -- 2.7.4