controller.js

import Ember from 'ember';
import { task } from 'ember-concurrency';

export default Ember.Controller.extend({

  parentTask: task(function* () {
    yield this.get('childTask').perform();
  }),

  childTask: task(function* () {
    throw new Error('childTask error');
  }),
});

template.hbs

<button {{action (perform parentTask)}}>parentTask</button>