int __init blk_dev_init(void)
{
	BUILD_BUG_ON(REQ_OP_LAST >= (1 << REQ_OP_BITS));
	BUILD_BUG_ON(REQ_OP_BITS + REQ_FLAG_BITS > 8 *
			FIELD_SIZEOF(struct request, cmd_flags));
	BUILD_BUG_ON(REQ_OP_BITS + REQ_FLAG_BITS > 8 *
			FIELD_SIZEOF(struct bio, bi_opf));

	/* used for unplugging and affects IO latency/throughput - HIGHPRI */
	kblockd_workqueue = alloc_workqueue("kblockd",
					    WQ_MEM_RECLAIM | WQ_HIGHPRI, 0);
	if (!kblockd_workqueue)
		panic("Failed to create kblockd\n");

	request_cachep = kmem_cache_create("blkdev_requests",
			sizeof(struct request), 0, SLAB_PANIC, NULL);

	blk_requestq_cachep = kmem_cache_create("request_queue",
			sizeof(struct request_queue), 0, SLAB_PANIC, NULL);

#ifdef CONFIG_DEBUG_FS
	blk_debugfs_root = debugfs_create_dir("block", NULL);
#endif

	return 0;
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.