Re: [PATCH v1 1/1] migration: Fix yank on postcopy multifd crashing guest after migration

[Leonardo Bras Soares Passos]

Hello Peter,

On Thu, Nov 24, 2022 at 1:04 PM Peter Xu <peterx@redhat.com> wrote:
>
> On Wed, Nov 09, 2022 at 02:56:29AM -0300, Leonardo Bras wrote:
> > diff --git a/migration/savevm.c b/migration/savevm.c
> > index a0cdb714f7..250caff7f4 100644
> > --- a/migration/savevm.c
> > +++ b/migration/savevm.c
> > @@ -1889,6 +1889,8 @@ static void *postcopy_ram_listen_thread(void *opaque)
> >          exit(EXIT_FAILURE);
> >      }
> >
> > +    migration_load_cleanup();
>
> It's a bit weird to call multifd-load-clean in a listen phase..

I agree.

>
> How about moving it right above
> trace_process_incoming_migration_co_postcopy_end_main()?  Then the new
> helper can also be static.

Seems a nice Idea to have this function to be static.

We have to guarantee this is run after the migration finished, but
before migration_incoming_state_destroy().

You suggested calling it right above of
trace_process_incoming_migration_co_postcopy_end_main(), which git
grep pointed me to an if clause in process_incoming_migration_co().
If I got the location correctly, it would not help: this coroutine is
ran just after the VM went to the target host, and not when the
migration finished.

If we are using multifd channels, this will break the migration with
segmentation fault (SIGSEGV), since the channels have not finished
sending yet.

Best regards,
Leo




>
> > +
> >      migrate_set_state(&mis->state, MIGRATION_STATUS_POSTCOPY_ACTIVE,
> >                                     MIGRATION_STATUS_COMPLETED);
> >      /*
> > --
> > 2.38.1
> >
>
> --
> Peter Xu
>