Re: [Qemu-devel] [PULL 3/3] vhost-user: Attempt to fix a race with set_mem_table.

[Michael S. Tsirkin]

On Fri, Aug 12, 2016 at 11:54:54AM -0400, Marc-André Lureau wrote:
> Hi
> 
> ----- Original Message -----
> > On Fri, Aug 12, 2016 at 03:20:56AM -0400, Marc-André Lureau wrote:
> > > Hi
> > > 
> > > ----- Original Message -----
> > > > sent a follow-up response to GET_FEATURES), I am now wondering if this
> > > > patch
> > > > may break existing vhost applications too ? If so, reverting it possibly
> > > > better.
> > > > What confuses me is why it doesn’t fail all the time, but only about 20%
> > > > to
> > > > 30% time as Fam reports.
> > > > 
> > > > Thoughts : Michael, Fam, MarcAndre ?
> > > 
> > > Indeed, I didn't ack that patch in the first place for that kind of
> > > reasons, so I would revert it.
> > > 
> > > thanks
> > 
> > I guess that's the safest thing to do for 2.7.
> > At least that's not any worse than 2.6.
> > I still think it's a good idea long term and test should be fixed,
> > but let's revert for now.
> > 
> 
> What about other backends that may have similar expectations from the 
> protocol.
> 
> This patch is a hack, there is no reason to have it upstream.

The reason is to avoid crashes with existing backends.

> The solution is provided with the REPLY_ACK patch.

It needs a backend update though.

But the issue is old, it's not a regression. I think we lose nothing
by pushing the work-around out until after 2.7.

-- 
MST