static void __loop_update_dio(struct loop_device *lo, bool dio)
{
	struct file *file = lo->lo_backing_file;
	struct address_space *mapping = file->f_mapping;
	struct inode *inode = mapping->host;
	unsigned short sb_bsize = 0;
	unsigned dio_align = 0;
	bool use_dio;

	if (inode->i_sb->s_bdev) {
		sb_bsize = bdev_logical_block_size(inode->i_sb->s_bdev);
		dio_align = sb_bsize - 1;
	}

	/*
	 * We support direct I/O only if lo_offset is aligned with the
	 * logical I/O size of backing device, and the logical block
	 * size of loop is bigger than the backing device's and the loop
	 * needn't transform transfer.
	 *
	 * TODO: the above condition may be loosed in the future, and
	 * direct I/O may be switched runtime at that time because most
	 * of requests in sane applications should be PAGE_SIZE aligned
	 */
	if (dio) {
		if (queue_logical_block_size(lo->lo_queue) >= sb_bsize &&
				!(lo->lo_offset & dio_align) &&
				mapping->a_ops->direct_IO &&
				!lo->transfer)
			use_dio = true;
		else
			use_dio = false;
	} else {
		use_dio = false;
	}

	if (lo->use_dio == use_dio)
		return;

	/* flush dirty pages before changing direct IO */
	vfs_fsync(file, 0);

	/*
	 * The flag of LO_FLAGS_DIRECT_IO is handled similarly with
	 * LO_FLAGS_READ_ONLY, both are set from kernel, and losetup
	 * will get updated by ioctl(LOOP_GET_STATUS)
	 */
	blk_mq_freeze_queue(lo->lo_queue);
	lo->use_dio = use_dio;
	if (use_dio) {
		queue_flag_clear_unlocked(QUEUE_FLAG_NOMERGES, lo->lo_queue);
		lo->lo_flags |= LO_FLAGS_DIRECT_IO;
	} else {
		queue_flag_set_unlocked(QUEUE_FLAG_NOMERGES, lo->lo_queue);
		lo->lo_flags &= ~LO_FLAGS_DIRECT_IO;
	}
	blk_mq_unfreeze_queue(lo->lo_queue);
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.