usb: misc: usbtest: add fix for driver hang

commit 53958751 upstream.

In sg_timeout(), req->status is set to "-ETIMEDOUT" before calling
into usb_sg_cancel(). usb_sg_cancel() will do nothing and return
directly if req->status has been set to a non-zero value. This will
cause driver hang whenever transfer time out is triggered.

This patch fixes this issue. It could be backported to stable kernel
with version later than v3.15.

Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Suggested-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/misc/usbtest.c

@@ -488,7 +488,6 @@ static void sg_timeout(unsigned long _req)
 {
 	struct usb_sg_request	*req = (struct usb_sg_request *) _req;
 
-	req->status = -ETIMEDOUT;
 	usb_sg_cancel(req);
 }
 
@@ -519,8 +518,10 @@ static int perform_sglist(
 		mod_timer(&sg_timer, jiffies +
 				msecs_to_jiffies(SIMPLE_IO_TIMEOUT));
 		usb_sg_wait(req);
-		del_timer_sync(&sg_timer);
-		retval = req->status;
+		if (!del_timer_sync(&sg_timer))
+			retval = -ETIMEDOUT;
+		else
+			retval = req->status;
 
 		/* FIXME check resulting data pattern */