How long can I stay on Exit/Re-entry visa from Saudi Arabia?

Hi, I'm taking a four-month long vacation and I'm planning to start my vacation by visiting Bahrain. I would reach Bahrain thru the causeway on an exit/re-entry visa, and would like to know how long I can stay there.

Correct me if I'm wrong, but I was told that I don't need to obtain a visit visa to visit Bahrain if I'm coming thru the causeway by bus, and that the exit/re-entry visa was enough. If that is true, how long can I stay there legally, and can I extend to more than a month on that exit/re-entry visa or do I need to obtain a visit visa after the maximum days allowed on exit/re-entry when I'm already in Bahrain? I'm asking because I plan to spend more than 30 days in Bahrain.

Thanks for your feedback.