As shortage is defined as a situation where an external mechanism prevents price from rising, technically it's a shortage where rent control is present, as rent control is the external mechanism that prevents price form rising. Economically, where price may freely increase, the price will rise until demand wanes to the point that there is no more need for additional housing. Socially, that is a problem as in the case of housing we want everyone to have the opportunity to have housing, which is why we bring in rent control, which then create shortages.