Re: [RFC v4 PATCH 45/49] multi-process/mig: Synchronize runstate of remote process

[Jag Raman]

On 11/11/2019 11:17 AM, Stefan Hajnoczi wrote:
> On Thu, Oct 24, 2019 at 05:09:26AM -0400, Jagannathan Raman wrote:
> > @@ -656,6 +657,19 @@ static void init_proxy(PCIDevice *dev, char *command, bool 
> > need_spawn, Error **e
> >       }
> >   }
> >   
> > +static void proxy_vm_state_change(void *opaque, int running, RunState state)
> > +{
> > +    PCIProxyDev *dev = opaque;
> > +    MPQemuMsg msg = { 0 };
> > +
> > +    msg.cmd = RUNSTATE_SET;
> > +    msg.bytestream = 0;
> > +    msg.size = sizeof(msg.data1);
> > +    msg.data1.runstate.state = state;
> > +
> > +    mpqemu_msg_send(dev->mpqemu_link, &msg, dev->mpqemu_link->com);
> > +}
>
> Changing vm state is a barrier operation - devices must not dirty memory
> afterwards.  This function doesn't have barrier semantics, it sends off
> the message without waiting for the remote process to finish processing
> it.  This means there is a race condition where QEMU has changes the vm
> state but devices could still dirty memory.  Please wait for a reply to
> prevent this.

Got it, thanks! Will do.

--
Jag

> Stefan