The USB stack calls during disconnect the esd_usb_disconnect() callback.
esd_usb_disconnect() calls netdev_unregister() for each network which
in turn calls the net_device_ops::ndo_stop callback esd_usb_close() if
the net device is up.

The esd_usb_close() callback tries to disable all CAN Ids and to reset
the CAN controller of the device sending appropriate control messages.

Sending these messages in .disconnect() is moot and always fails because
either the device is gone or the USB communication is already torn down
by the USB stack in the course of a rmmod operation.

This patch moves the code that sends these control messages to a new
function esd_usb_stop() which is approximately the counterpart of
esd_usb_start() to make code structure less convoluted.

It then changes esd_usb_close() not to send the control messages at
all if the ndo_stop() callback is executed from the USB .disconnect()
callback. A new flag in_usb_disconnect is added to the struct esd_usb
device structure to mark this condition which is checked by
esd_usb_close() whether to skip the send operations in esd_usb_start().

Signed-off-by: Stefan Mätje <stefan.maetje@esd.eu>
---
 drivers/net/can/usb/esd_usb.c | 34 ++++++++++++++++++++++++++--------
 1 file changed, 26 insertions(+), 8 deletions(-)

diff --git a/drivers/net/can/usb/esd_usb.c b/drivers/net/can/usb/esd_usb.c
index 8e6688f10451..0196394c5986 100644
--- a/drivers/net/can/usb/esd_usb.c
+++ b/drivers/net/can/usb/esd_usb.c
@@ -281,6 +281,7 @@ struct esd_usb {
 	int net_count;
 	u32 version;
 	int rxinitdone;
+	int in_usb_disconnect;
 	void *rxbuf[ESD_USB_MAX_RX_URBS];
 	dma_addr_t rxbuf_dma[ESD_USB_MAX_RX_URBS];
 };
@@ -1047,9 +1048,9 @@ static netdev_tx_t esd_usb_start_xmit(struct sk_buff *skb,
 	return ret;
 }
 
-static int esd_usb_close(struct net_device *netdev)
+/* Stop interface */
+static int esd_usb_stop(struct esd_usb_net_priv *priv)
 {
-	struct esd_usb_net_priv *priv = netdev_priv(netdev);
 	union esd_usb_msg *msg;
 	int err;
 	int i;
@@ -1066,8 +1067,10 @@ static int esd_usb_close(struct net_device *netdev)
 	for (i = 0; i <= ESD_USB_MAX_ID_SEGMENT; i++)
 		msg->filter.mask[i] = 0;
 	err = esd_usb_send_msg(priv->usb, msg);
-	if (err < 0)
-		netdev_err(netdev, "sending idadd message failed: %pe\n", ERR_PTR(err));
+	if (err < 0) {
+		netdev_err(priv->netdev, "sending idadd message failed: %pe\n", ERR_PTR(err));
+		goto bail;
+	}
 
 	/* set CAN controller to reset mode */
 	msg->hdr.len = sizeof(struct esd_usb_set_baudrate_msg) / sizeof(u32); /* # of 32bit words */
@@ -1077,7 +1080,23 @@ static int esd_usb_close(struct net_device *netdev)
 	msg->setbaud.baud = cpu_to_le32(ESD_USB_NO_BAUDRATE);
 	err = esd_usb_send_msg(priv->usb, msg);
 	if (err < 0)
-		netdev_err(netdev, "sending setbaud message failed: %pe\n", ERR_PTR(err));
+		netdev_err(priv->netdev, "sending setbaud message failed: %pe\n", ERR_PTR(err));
+
+bail:
+	kfree(msg);
+
+	return err;
+}
+
+static int esd_usb_close(struct net_device *netdev)
+{
+	struct esd_usb_net_priv *priv = netdev_priv(netdev);
+	int err = 0;
+
+	if (!priv->usb->in_usb_disconnect) {
+		/* It's moot to try this in usb_disconnect()! */
+		err = esd_usb_stop(priv);
+	}
 
 	priv->can.state = CAN_STATE_STOPPED;
 
@@ -1085,9 +1104,7 @@ static int esd_usb_close(struct net_device *netdev)
 
 	close_candev(netdev);
 
-	kfree(msg);
-
-	return 0;
+	return err;
 }
 
 static const struct net_device_ops esd_usb_netdev_ops = {
@@ -1439,6 +1456,7 @@ static void esd_usb_disconnect(struct usb_interface *intf)
 	usb_set_intfdata(intf, NULL);
 
 	if (dev) {
+		dev->in_usb_disconnect = 1;
 		for (i = 0; i < dev->net_count; i++) {
 			if (dev->nets[i]) {
 				netdev = dev->nets[i]->netdev;
-- 
2.34.1