w1: do not unlock unheld list_mutex in __w1_remove_master_device()

w1_process_callbacks() expects to be called with dev->list_mutex held,
but it is the fact only in w1_process(). __w1_remove_master_device()
calls w1_process_callbacks() after it releases list_mutex.

The patch fixes __w1_remove_master_device() to acquire list_mutex
for w1_process_callbacks().

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Acked-by: David Fries <david@fries.net>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Cc: stable <stable@vger.kernel.org> # 3.15
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/w1/w1.c

@@ -1078,6 +1078,8 @@ static void w1_search_process(struct w1_master *dev, u8 search_type)
  * w1_process_callbacks() - execute each dev->async_list callback entry
  * @dev: w1_master device
  *
+ * The w1 master list_mutex must be held.
+ *
  * Return: 1 if there were commands to executed 0 otherwise
  */
 int w1_process_callbacks(struct w1_master *dev)

drivers/w1/w1_int.c

@@ -219,9 +219,13 @@ void __w1_remove_master_device(struct w1_master *dev)
 
 		if (msleep_interruptible(1000))
 			flush_signals(current);
+		mutex_lock(&dev->list_mutex);
 		w1_process_callbacks(dev);
+		mutex_unlock(&dev->list_mutex);
 	}
+	mutex_lock(&dev->list_mutex);
 	w1_process_callbacks(dev);
+	mutex_unlock(&dev->list_mutex);
 
 	memset(&msg, 0, sizeof(msg));
 	msg.id.mst.id = dev->id;