Re: [PATCH] runstate: ignore exit request in finish migrate state

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Paolo Bonzini (pbonzini@redhat.com) wrote:
> On 17/10/19 12:18, Laurent Vivier wrote:
> > Trying to reboot a VM while a migration is running can
> > move to the prelaunch state (because of the reset) while
> > the runstate is in finish migrate state.
> > As the logical step after the finish migrate is postmigrate,
> > this can create an invalid state transition from prelaunch state
> > to postmigrate state and this raises an error and aborts:
> > 
> >     invalid runstate transition: 'prelaunch' -> 'postmigrate'
> > 
> > As we are not able to manage reset in finish migrate state the
> > best we can do is to ignore any changes and delay them until
> > the next state which should be postmigrate and which should allow
> > this kind of transition.
> > 
> > Reported-by: Lukáš Doktor <ldoktor@redhat.com>
> > Suggested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> > ---
> >  vl.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/vl.c b/vl.c
> > index 0a295e5d77d6..dc71c822ba24 100644
> > --- a/vl.c
> > +++ b/vl.c
> > @@ -1744,6 +1744,9 @@ static bool main_loop_should_exit(void)
> >      RunState r;
> >      ShutdownCause request;
> >  
> > +    if (runstate_check(RUN_STATE_FINISH_MIGRATE)) {
> > +        return false;
> > +    }
> >      if (preconfig_exit_requested) {
> >          if (runstate_check(RUN_STATE_PRECONFIG)) {
> >              runstate_set(RUN_STATE_PRELAUNCH);
> > 
> 
> Your patch makes sense, but I don't understand this function very much.
>  In particular I don't understand why it returns true when
> preconfig_exit_requested is true.  Wouldn't that cause main_loop() and
> thus QEMU to exit?  Igor, can you help?

It's because we now run main_loop() twice; once in the preconfig state
and once the main main loop.


4323     /* do monitor/qmp handling at preconfig state if requested */
4324     main_loop();

....

4452     os_setup_post();
4453 
4454     main_loop();
4455 
4456     gdbserver_cleanup();

> Paolo

Dave

--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK