Almost any aircraft can be rolled (positive roll. Can't see a 172 being capable of an outside roll, pathetic roll rate). If it goes well there will be no harm done to aircraft or pax by a barrel roll. However if it is not done correctly then it might spin (not bad in a 172, but not good in other aircraft) or more likely the nose might come down too far, risking either exceeding VNE or overstressing to avoid doing so.
Don't do it people.
P.S. Cloudbasher is right. It always annoyed me when people described the barrel roll as a 1g manoeuvre.