USB: report submission of active URBs

This patch (as1633) changes slightly the way usbcore handled
submissions of URBs that are already active.  It will now return
-EBUSY rather than -EINVAL, and it will call WARN_ONCE to draw
people's attention to the bug.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/usb/error-codes.txt

@@ -21,6 +21,8 @@ Non-USB-specific:
 
 USB-specific:
 
+-EBUSY		The URB is already active.
+
 -ENODEV		specified USB-device or bus doesn't exist
 
 -ENOENT		specified interface or endpoint does not exist or

drivers/usb/core/urb.c

@@ -321,8 +321,13 @@ int usb_submit_urb(struct urb *urb, gfp_t mem_flags)
 	struct usb_host_endpoint	*ep;
 	int				is_out;
 
-	if (!urb || urb->hcpriv || !urb->complete)
+	if (!urb || !urb->complete)
 		return -EINVAL;
+	if (urb->hcpriv) {
+		WARN_ONCE(1, "URB %p submitted while active\n", urb);
+		return -EBUSY;
+	}
+
 	dev = urb->dev;
 	if ((!dev) || (dev->state < USB_STATE_UNAUTHENTICATED))
 		return -ENODEV;