void blk_free_flush_queue(struct blk_flush_queue *fq)
{
	/* bio based request queue hasn't flush queue */
	if (!fq)
		return;

	kfree(fq->flush_rq);
	kfree(fq);
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.