Como esperar que o item da lista de mangusto seja empurrado?

router.post('/get/:faultId/new_comment', function(req, res, next) {
  var commenter = req.body.first_name + " " + req.body.last_name;
  var comment = req.body.new_comment_text
  var datetime = Date.now();

  var comment_object = commentCreate(commenter, comment, datetime);

  FaultReport
    .findOne({
      '_id': req.params.faultId
    })
    .exec(function(err, report) {
      if (err) return console.error(err);
      report.comment.push(comment_object);
      report.save(function(err) {
        res.redirect('/api/get/' + req.params.faultId);
      });
    });
});