Your cracks are being caused by the foundation settleing and the stress is transferred up and to the weakest area to crack, that is the drywall.
The cracks will always come back, you can now consider this crack your expansion joint.
What I would do is to get some latex/silicon PAINTABLE, white caulk and force it into the crack and let it dry then paint over it. This will expand/contract with the foundation and allow you some movement before it cracks again, then just refill it again.
In my experience, no matter what you do to try to remedy this it will not go away UNLESS you have foundation work done.