Patch "cdc_ether: Fix handling connection notification" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

cdc_ether: Fix handling connection notification

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
cdc_ether-fix-handling-connection-notification.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Kristian Evensen <[email protected]>
Date: Thu, 1 Dec 2016 14:23:17 +0100
Subject: cdc_ether: Fix handling connection notification

From: Kristian Evensen <[email protected]>

[ Upstream commit d5c83d0d1d83b3798c71e0c8b7c3624d39c91d88 ]

Commit bfe9b9d2df66 ("cdc_ether: Improve ZTE MF823/831/910 handling") introduced a work-around in usbnet_cdc_status() for devices that exported cdc carrier on twice on connect. Before the commit, this behavior caused the link state to be incorrect. It was assumed that all CDC Ethernet devices would either export this behavior, or send one off and then one on notification (which seems to be the default behavior).

Unfortunately, it turns out multiple devices sends a connection notification multiple times per second (via an interrupt), even when connection state does not change. This has been observed with several different USB LAN dongles (at least), for example 13b1:0041 (Linksys). After bfe9b9d2df66, the link state has been set as down and then up for each notification. This has caused a flood of Netlink NEWLINK messages and syslog to be flooded with messages similar to:

cdc_ether 2-1:2.0 eth1: kevent 12 may have been dropped

This commit fixes the behavior by reverting usbnet_cdc_status() to how it was before bfe9b9d2df66. The work-around has been moved to a separate status-function which is only called when a known, affect device is detected.

v1->v2:

* Do not open-code netif_carrier_ok() (thanks Henning Schild).
* Call netif_carrier_off() instead of usb_link_change(). This prevents calling schedule_work() twice without giving the work queue a chance to be processed (thanks Bjørn Mork).

---
 drivers/net/usb/cdc_ether.c |   38 +++++++++++++++++++++++++++++++-------
 1 file changed, 31 insertions(+), 7 deletions(-)

@@ -388,12 +388,6 @@ void usbnet_cdc_status(struct usbnet *de
 	case USB_CDC_NOTIFY_NETWORK_CONNECTION:
 		netif_dbg(dev, timer, dev->net, "CDC: carrier %s\n",
 			  event->wValue ? "on" : "off");
-
-		/* Work-around for devices with broken off-notifications */
-		if (event->wValue &&
-		    !test_bit(__LINK_STATE_NOCARRIER, &dev->net->state))
-			usbnet_link_change(dev, 0, 0);
-
 		usbnet_link_change(dev, !!event->wValue, 0);
 		break;
 	case USB_CDC_NOTIFY_SPEED_CHANGE:	/* tx/rx rates */

@@ -466,6 +460,36 @@ static int usbnet_cdc_zte_rx_fixup(struc
 	return 1;
 }
 
+/* Ensure correct link state
+ *
+ * Some devices (ZTE MF823/831/910) export two carrier on notifications when
+ * connected. This causes the link state to be incorrect. Work around this by
+ * always setting the state to off, then on.
+ */
+void usbnet_cdc_zte_status(struct usbnet *dev, struct urb *urb)
+{
+	struct usb_cdc_notification *event;
+
+	if (urb->actual_length < sizeof(*event))
+		return;
+
+	event = urb->transfer_buffer;
+
+	if (event->bNotificationType != USB_CDC_NOTIFY_NETWORK_CONNECTION) {
+		usbnet_cdc_status(dev, urb);
+		return;
+	}
+
+	netif_dbg(dev, timer, dev->net, "CDC: carrier %s\n",
+		  event->wValue ? "on" : "off");
+
+	if (event->wValue &&
+	    netif_carrier_ok(dev->net))
+		netif_carrier_off(dev->net);
+
+	usbnet_link_change(dev, !!event->wValue, 0);
+}
+
 static const struct driver_info	cdc_info = {
 	.description =	"CDC Ethernet Device",
 	.flags =	FLAG_ETHER | FLAG_POINTTOPOINT,

@@ -481,7 +505,7 @@ static const struct driver_info	zte_cdc_
 	.flags =	FLAG_ETHER | FLAG_POINTTOPOINT,
 	.bind =		usbnet_cdc_zte_bind,
 	.unbind =	usbnet_cdc_unbind,
-	.status =	usbnet_cdc_status,
+	.status =	usbnet_cdc_zte_status,
 	.set_rx_mode =	usbnet_cdc_update_filter,
 	.manage_power =	usbnet_manage_power,
 	.rx_fixup = usbnet_cdc_zte_rx_fixup,

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/cdc_ether-fix-handling-connection-notification.patch