No barrier needed. However you should already have one there. It should be the one on the fiberglass insulation if its still there. If not, do not worry about this.
Be sure to put in baffles on the roof edge near the overhang/soffit to prevent the cellulose insulation from falling into the soffit area.
Also before you begin, I would suggest that you seal any openings around pipes, wires and along any exposed top wall plates from the rooms below. Air moving through the insulation is the biggest robber of heat out of your home. Think of it as a warm sweater. Works great, until there is a slight breeze outside. Then the sweater does not work quite as well. The same thing happens with insulation. If air blows into it or through it it looses its "R" value thus you loose heat.
last note. Your going to need quite a lot of this insulation to generate a good R value. Doing so can bury wire boxes and all sorts of important things that sometime you may need access to. We staple ribbons on the rafters directly above any electrical splice boxes, cable wires etc when we do this. Therefor in the future you are not looking all over the place for that one box that is buried.
Get suggestion of locating jboxes, etc.