ALWAYS okay.
If the seat reclines, it's your prerogative to use it. It is incumbent upon the person aft to work with the space provided.
I had a woman last week try to keep me from reclining at all in transcon C.
I'm training for an event, so I got up early to run 15 miles before the flight.
Recline is a feature. You paid for your ticket. Use the feature at will.
When the person in front of me reclines, and I can't open my laptop all the way, I don't open my laptop all the way. Period.