Re: [Qemu-devel] [RFC PATCH] vl: fix migration when watchdog expires

[Paolo Bonzini]

On 14/08/2018 12:48, Jay Zhou wrote:
> I got the following error when migrating a VM with watchdog
> device:
> 
> {"timestamp": {"seconds": 1533884471, "microseconds": 668099},
> "event": "WATCHDOG", "data": {"action": "reset"}}
> {"timestamp": {"seconds": 1533884471, "microseconds": 677658},
> "event": "RESET", "data": {"guest": true}}
> {"timestamp": {"seconds": 1533884471, "microseconds": 677874},
> "event": "STOP"}
> qemu-system-x86_64: invalid runstate transition: 'prelaunch' -> 'postmigrate'
> Aborted
> 
> The run state transition is RUN_STATE_FINISH_MIGRATE to RUN_STATE_PRELAUNCH,
> then the migration thread aborted when it tries to set RUN_STATE_POSTMIGRATE.
> There is a race between the main loop thread and the migration thread I think.

In that case I think you shouldn't go to POSTMIGRATE at all, because the
VM has been reset.

Alternatively, when the watchdog fires in RUN_STATE_FINISH_MIGRATE
state, it might delay the action until after the "cont" command is
invoked on the source, but I'm not sure what's the best way to achieve
that...

Paolo