Re: [Qemu-devel] [PATCH 0/4] qtest: fix "device_del" out-of-order events

[Thomas Huth]

On 13.09.2017 11:36, Peter Xu wrote:
> It starts from a "make check" failure on one of my private tree. The
> problem is that when we do "device_del" we normally looking for two
> things: one response (which is mostly empty), and a REMOVE event.  The
> tricky point is the event can either be there before/after the empty
> response.  So I added qmp_device_del() to make sure the order does not
> matter, then use it where proper.
> 
> Since I'm at it, I also added the sister helper qmp_device_add(), it
> helps to remove LOCs.

I've had a similar idea a couple of weeks ago, see here:

http://patchwork.ozlabs.org/patch/801487/

> I still don't 100% sure why my private tree can trigger this error,
> while the master cannot. Anyway, I think this is something we should
> have, no matter what.

Did you maybe touch the USB tests in your private tree?
As far as I know, some test currently use QMP in a bad way, for example
usb_test_hotplug() only checks for the DEVICE_DELETED at the end, but
forgets to read back the final return value. That return value is then
presented to the next part of the code that uses QMP instead ... it
currently only works more or less by accident, but as soon as you try to
add new code inbetween, it certainly will fail.
==> We really got to clean this up (either with my patch or your patch
series).

 Thomas