Using ConfigureAwait(false) on tasks passed in to Task.WhenAll() fails

You only need ConfigureAwait when you actually perform the await, the correct form would be

[HttpGet]
public async Task<JsonResult> doAsyncStuff()
{
  var t1 = this.service1.task1();
  var t2 = this.service2.task2();
  var t3 = this.service3.task3();
  var t4 = this.service4.task4();

  await Task.WhenAll(t1,t2,t3,t4).ConfigureAwait(false);
  return this.Json(new {redirect = true, href = Url.Action("Blah")}, JsonRequestBehavior.AllowGet);
}