USB: fix oops on disconnect in cdc-acm

This patch fixes an oops caused when during an unplug a device's table
of endpoints is zeroed before the driver is notified. A pointer to
the endpoint must be cached.

this fixes a regression caused by commit
5186ffee2320942c3dc9745f7930e0eb15329ca6
Therefore it should go into 2.6.31

Signed-off-by: Oliver Neukum <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/class/cdc-acm.c

···
 	struct acm_ru *rcv;
 	unsigned long flags;
 	unsigned char throttled;
-	struct usb_host_endpoint *ep;
 
 	dbg("Entering acm_rx_tasklet");
 
···
 
 		rcv->buffer = buf;
 
-		ep = (usb_pipein(acm->rx_endpoint) ? acm->dev->ep_in : acm->dev->ep_out)
-				[usb_pipeendpoint(acm->rx_endpoint)];
-		if (usb_endpoint_xfer_int(&ep->desc))
+		if (acm->is_int_ep)
 			usb_fill_int_urb(rcv->urb, acm->dev,
 					 acm->rx_endpoint,
 					 buf->base,
 					 acm->readsize,
-					 acm_read_bulk, rcv, ep->desc.bInterval);
+					 acm_read_bulk, rcv, acm->bInterval);
 		else
 			usb_fill_bulk_urb(rcv->urb, acm->dev,
 					  acm->rx_endpoint,
···
 	spin_lock_init(&acm->read_lock);
 	mutex_init(&acm->mutex);
 	acm->rx_endpoint = usb_rcvbulkpipe(usb_dev, epread->bEndpointAddress);
+	acm->is_int_ep = usb_endpoint_xfer_int(epread);
+	if (acm->is_int_ep)
+		acm->bInterval = epread->bInterval;
 	tty_port_init(&acm->port);
 	acm->port.ops = &acm_port_ops;
 

drivers/usb/class/cdc-acm.h

···
 	unsigned int ctrl_caps;				/* control capabilities from the class specific header */
 	unsigned int susp_count;			/* number of suspended interfaces */
 	int combined_interfaces:1;			/* control and data collapsed */
+	int is_int_ep:1;				/* interrupt endpoints contrary to spec used */
+	u8 bInterval;
 	struct acm_wb *delayed_wb;			/* write queued for a device about to be woken */
 };