static void __netdev_adjacent_dev_unlink_neighbour(struct net_device *dev,
						   struct net_device *upper_dev)
{
	__netdev_adjacent_dev_unlink_lists(dev, upper_dev, 1,
					   &dev->adj_list.upper,
					   &upper_dev->adj_list.lower);
}

The product dereferences a pointer that it expects to be valid but is NULL.