void blk_account_io_done(struct request *req, u64 now)
{
	/*
	 * Account IO completion.  flush_rq isn't accounted as a
	 * normal IO on queueing nor completion.  Accounting the
	 * containing request is enough.
	 */
	if (blk_do_io_stat(req) && !(req->rq_flags & RQF_FLUSH_SEQ)) {
		unsigned long duration;
		const int sgrp = op_stat_group(req_op(req));
		struct hd_struct *part;
		int cpu;

		duration = nsecs_to_jiffies(now - req->start_time_ns);
		cpu = part_stat_lock();
		part = req->part;

		part_stat_inc(cpu, part, ios[sgrp]);
		part_stat_add(cpu, part, ticks[sgrp], duration);
		part_round_stats(req->q, cpu, part);
		part_dec_in_flight(req->q, part, rq_data_dir(req));

		hd_struct_put(part);
		part_stat_unlock();
	}
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.