static void ath_tx_queue_tid(struct ath_txq *txq, struct ath_atx_tid *tid)
{
	struct ath_atx_ac *ac = tid->ac;

	if (tid->paused)
		return;

	if (tid->sched)
		return;

	tid->sched = true;
	list_add_tail(&tid->list, &ac->tid_q);

	if (ac->sched)
		return;

	ac->sched = true;
	list_add_tail(&ac->list, &txq->axq_acq);
}

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.