USB: serial: ti_usb_3410_5052: fix port-close races

Fix races between closing a port and opening or closing another port on
the same device which could lead to a failure to start or stop the
shared interrupt URB. The latter could potentially cause a
use-after-free or worse in the completion handler on driver unbind.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/ti_usb_3410_5052.c

@@ -776,7 +776,6 @@ static void ti_close(struct usb_serial_port *port)
 	struct ti_port *tport;
 	int port_number;
 	int status;
-	int do_unlock;
 	unsigned long flags;
 
 	tdev = usb_get_serial_data(port->serial);
@@ -800,16 +799,13 @@ static void ti_close(struct usb_serial_port *port)
 			"%s - cannot send close port command, %d\n"
 							, __func__, status);
 
-	/* if mutex_lock is interrupted, continue anyway */
-	do_unlock = !mutex_lock_interruptible(&tdev->td_open_close_lock);
+	mutex_lock(&tdev->td_open_close_lock);
 	--tport->tp_tdev->td_open_port_count;
-	if (tport->tp_tdev->td_open_port_count <= 0) {
+	if (tport->tp_tdev->td_open_port_count == 0) {
 		/* last port is closed, shut down interrupt urb */
 		usb_kill_urb(port->serial->port[0]->interrupt_in_urb);
-		tport->tp_tdev->td_open_port_count = 0;
 	}
-	if (do_unlock)
-		mutex_unlock(&tdev->td_open_close_lock);
+	mutex_unlock(&tdev->td_open_close_lock);
 }