Don't call the landlord or police etc - at least not until you've tried talking to them. No need to create more drama where it's not needed.
Chances are they aren't aware how badly they are stinking up everyone else's place. A quiet word asking them to open a window when they smoke could well do the trick (if you have a central aircon type system, then turning that off when they smoke will also help).
If they're unreasonable and/or abusive when you go speak to them, then consider informing the landlord (or, first, threatening to). It sounds like you're living in a fairly reasonable area though, so chances are good that they will be cooperative.