Wikipedia says that " Illustrations in the 13th century Maciejowski Bible show a short staffed weapon with a long blade used by both infantry and cavalry." with reference to the glaive (which is about 7 or 8 feet long).
According to lostkingdom.net, the Kontos was used by Roman and Byzantine cavalry and was essentially a 12-ft long spear. It was problematic, though. Anything that large needs two hands which means that one must steer the horse with their knees; which is probably easier with a celtic/roman saddle than with one with stirrups. http://www.lostkingdom.net/historical-polearms/ is a great link to help with your query.
In general, I don't think that pole-arms were particularly effective when wielded by cavalry (with the exception of the lance) because of how unwieldy they were. The main purpose of a pole-arm is to keep the enemy away (either cavalry or infantry) and were favored by less trained fighters. Cavalry were typically the more trained elite and their entire purpose was to close with the enemy and chase them down after they broke ranks and fled.
I hope this helps,