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

[Paolo Bonzini <pbonzini@redhat.com>]

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?

Paolo