static struct request *blk_old_get_request(struct request_queue *q,
				unsigned int op, blk_mq_req_flags_t flags)
{
	struct request *rq;
	gfp_t gfp_mask = flags & BLK_MQ_REQ_NOWAIT ? GFP_ATOMIC : GFP_NOIO;
	int ret = 0;

	WARN_ON_ONCE(q->mq_ops);

	/* create ioc upfront */
	create_io_context(gfp_mask, q->node);

	ret = blk_queue_enter(q, flags);
	if (ret)
		return ERR_PTR(ret);
	spin_lock_irq(q->queue_lock);
	rq = get_request(q, op, NULL, flags, gfp_mask);
	if (IS_ERR(rq)) {
		spin_unlock_irq(q->queue_lock);
		blk_queue_exit(q);
		return rq;
	}

	/* q->queue_lock is unlocked at this point */
	rq->__data_len = 0;
	rq->__sector = (sector_t) -1;
	rq->bio = rq->biotail = NULL;
	return rq;
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.