ASBI Pocket Beit Midrash: Aruch HaShulhan, Laws of Synagogue 151:5

And one can question the current practice to be lenient about speaking in the synagogue or beit midrash following prayers about all manner of mundane topics to a degree that this behavior seems to be permissible. And it appears to me that they base themselves on the position of Ramban who explains that synagogues in the diaspora are built on condition that even while they are in operation as synagogues they can be used for other needed purposes. And we think mundane conversations are needed. Each individual decides for himself. However, it is certainly forbidden to smoke "bitter leaves" in shul for there is no greater form of light-headedness than this. And it is only permissible for those who spend all day or half the day in the beit midrash studying Torah to smoke since this is like eating for them. But that smoking can only take place in a beit midrash and not a synagogue. And any other person who does not spend all day learning Torah in the beit midrash cannot smoke there and no condition put in place when the beit midrash was built can make this permissible. And so it is appropriate to rebuke those who do.