I've got a screened-in porch on my 11-yr old house, and was attempting to
re-paint the ceiling. As I was rolling on the paint, the old paint starting
coming off on the roller.

Upon inspection the old paint is barely attached to the drywall ceiling. I'm
able to peel the old paint and drywall tape away. I'm wondering if there was
no primer applied to the drywall and/or interior paint was used. Also it
looks like drywall tape was used over the joint compound, but no mud was
used over the tape.

In any case, I've now got a ceiling that has large sections of drywall
exposed, missing drywall tape (so joint compound is exposed), and sections
where the old paint is still sticking somewhat okay.

What's the best way to get the ceiling to a paintable condition? Am I going
to have to chip away at the old paint or is there a product that will bind
to the old paint and keep it from peeling away from the drywall. Perhaps a
primer since I'm going to have to re-prime the exposed drywall anyway?

I've got Behr exterior latex paint that I was using before the old paint
started peeling away, I've never had a problem with Behr before but could it
be the cause?