usb: legousbtower: use irqsave() in USB's complete callback

The USB completion callback does not disable interrupts while acquiring
the lock. We want to remove the local_irq_disable() invocation from
__usb_hcd_giveback_urb() and therefore it is required for the callback
handler to disable the interrupts while acquiring the lock.
The callback may be invoked either in IRQ or BH context depending on the
USB host controller.
Use the _irqsave() variant of the locking primitives.

Cc: Juergen Stuber <starblue@users.sourceforge.net>
Cc: legousb-devel@lists.sourceforge.net
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/legousbtower.c

@@ -722,6 +722,7 @@ static void tower_interrupt_in_callback (struct urb *urb)
 	struct lego_usb_tower *dev = urb->context;
 	int status = urb->status;
 	int retval;
+	unsigned long flags;
 
 	lego_usb_tower_debug_data(&dev->udev->dev, __func__,
 				  urb->actual_length, urb->transfer_buffer);
@@ -740,7 +741,7 @@ static void tower_interrupt_in_callback (struct urb *urb)
 	}
 
 	if (urb->actual_length > 0) {
-		spin_lock (&dev->read_buffer_lock);
+		spin_lock_irqsave(&dev->read_buffer_lock, flags);
 		if (dev->read_buffer_length + urb->actual_length < read_buffer_size) {
 			memcpy (dev->read_buffer + dev->read_buffer_length,
 				dev->interrupt_in_buffer,
@@ -753,7 +754,7 @@ static void tower_interrupt_in_callback (struct urb *urb)
 			pr_warn("read_buffer overflow, %d bytes dropped\n",
 				urb->actual_length);
 		}
-		spin_unlock (&dev->read_buffer_lock);
+		spin_unlock_irqrestore(&dev->read_buffer_lock, flags);
 	}
 
 resubmit: