Re: [PATCH v8 17/20] multi-process: heartbeat messages to remote

[Stefan Hajnoczi]

On Fri, Aug 14, 2020 at 04:01:47PM -0700, Elena Ufimtseva wrote:
> On Tue, Aug 11, 2020 at 03:41:30PM +0100, Stefan Hajnoczi wrote:
> > On Fri, Jul 31, 2020 at 02:20:24PM -0400, Jagannathan Raman wrote:
> > > @@ -343,3 +349,49 @@ static void probe_pci_info(PCIDevice *dev, Error 
> > > **errp)
> > >          }
> > >      }
> > >  }
> > > +
> > > +static void hb_msg(PCIProxyDev *dev)
> > > +{
> > > +    DeviceState *ds = DEVICE(dev);
> > > +    Error *local_err = NULL;
> > > +    MPQemuMsg msg = { 0 };
> > > +
> > > +    msg.cmd = PROXY_PING;
> > > +    msg.bytestream = 0;
> > > +    msg.size = 0;
> > > +
> > > +    (void)mpqemu_msg_send_and_await_reply(&msg, dev->ioc, &local_err);
> > > +    if (local_err) {
> > > +        error_report_err(local_err);
> > > +        qio_channel_close(dev->ioc, &local_err);
> > > +        error_setg(&error_fatal, "Lost contact with device %s", ds->id);
> > > +    }
> > > +}
> > 
> > Here is my feedback from the last revision. Was this addressed?
> >
> 
> Hi Stefan,
> 
> Thank you for reviewing the patchset. In this version we decided to 
> shutdown the guest when the heartbeat did not get a reply from the
> remote by setting the error_fatal.
> Should we approach it differently or you prefer us to get rid of the
> heartbeat in this form?

I think the only case that this patch handles is when the mpqemu channel
is closed.

The VM hangs when the channel is still open but the remote is
unresponsive. (mpqemu_msg_send_and_await_reply() calls aio_poll() with
the global mutex held so vcpus cannot make progress.)

The heartbeat mechanism needs to handle the case where the other side
isn't responding. It can't hang QEMU.

I suggest dropping this patch. It can be done later.

Stefan

signature.asc
Description: PGP signature