static void coroutine_fn v9fs_flush(void *opaque)
{
    ssize_t err;
    int16_t tag;
    size_t offset = 7;
    V9fsPDU *cancel_pdu = NULL;
    V9fsPDU *pdu = opaque;
    V9fsState *s = pdu->s;

    err = pdu_unmarshal(pdu, offset, "w", &tag);
    if (err < 0) {
        pdu_complete(pdu, err);
        return;
    }
    trace_v9fs_flush(pdu->tag, pdu->id, tag);

    if (pdu->tag == tag) {
        warn_report("the guest sent a self-referencing 9P flush request");
    } else {
        QLIST_FOREACH(cancel_pdu, &s->active_list, next) {
            if (cancel_pdu->tag == tag) {
                break;
            }
        }
    }
    if (cancel_pdu) {
        cancel_pdu->cancelled = 1;
        /*
         * Wait for pdu to complete.
         */
        qemu_co_queue_wait(&cancel_pdu->complete, NULL);
        if (!qemu_co_queue_next(&cancel_pdu->complete)) {
            cancel_pdu->cancelled = 0;
            pdu_free(cancel_pdu);
        }
    }
    pdu_complete(pdu, 7);
}

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.