Re: [REGRESSION] Select hang with zero sized UDP packets

From: Laura Abbott <redacted>
Date: Tue, 23 Aug 2016 10:53:26 -0700

Fedora received a report[1] of a unit test failing on Ruby when using
the
4.7 kernel. This was a test to send a zero sized UDP packet. With the
4.7 kernel, the test now timing out on a select instead of completing.
The reduced ruby test is

  def test_udp_recvfrom_nonblock
    u1 = UDPSocket.new
    u2 = UDPSocket.new
    u1.bind("127.0.0.1", 0)
    u2.send("", 0, u1.getsockname)
    IO.select [u1]  # test gets stuck here
  ensure
    u1.close if u1
    u2.close if u2
  end

Well, if there is no data, should select really wake up?

I think it's valid not to.