static ssize_t pdu_marshal(V9fsPDU *pdu, size_t offset, const char *fmt, ...)
{
    ssize_t ret;
    va_list ap;

    va_start(ap, fmt);
    ret = pdu->s->transport->pdu_vmarshal(pdu, offset, fmt, ap);
    va_end(ap);

    return ret;
}

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.