Re: [PATCH V2 04/11] migration: stop vm earlier for cpr

[Steven Sistare]

On 7/22/2024 9:42 AM, Fabiano Rosas wrote:
> Steven Sistare <steven.sistare@oracle.com> writes:
>
> > On 7/17/2024 2:59 PM, Fabiano Rosas wrote:
> > > Steve Sistare <steven.sistare@oracle.com> writes:
> > >
> > > > Stop the vm earlier for cpr, to guarantee consistent device state when
> > > > CPR state is saved.
> > > >
> > > > Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> > > > ---
> > > >    migration/migration.c | 22 +++++++++++++---------
> > > >    1 file changed, 13 insertions(+), 9 deletions(-)
> > > >
> > > > diff --git a/migration/migration.c b/migration/migration.c
> > > > index 0f47765..8a8e927 100644
> > > > --- a/migration/migration.c
> > > > +++ b/migration/migration.c
> > > > @@ -2077,6 +2077,7 @@ void qmp_migrate(const char *uri, bool has_channels,
> > > >        MigrationState *s = migrate_get_current();
> > > >        g_autoptr(MigrationChannel) channel = NULL;
> > > >        MigrationAddress *addr = NULL;
> > > > +    bool stopped = false;
> > > >    
> > > >        /*
> > > >         * Having preliminary checks for uri and channel
> > > > @@ -2120,6 +2121,15 @@ void qmp_migrate(const char *uri, bool has_channels,
> > > >            }
> > > >        }
> > > >    
> > > > +    if (migrate_mode_is_cpr(s)) {
> > > > +        int ret = migration_stop_vm(s, RUN_STATE_FINISH_MIGRATE);
> > > > +        if (ret < 0) {
> > > > +            error_setg(&local_err, "migration_stop_vm failed, error %d", -ret);
> > > > +            goto out;
> > > > +        }
> > > > +        stopped = true;
> > > > +    }
> > > > +
> > > >        if (cpr_state_save(&local_err)) {
> > > >            goto out;
> > > >        }
> > > > @@ -2155,6 +2165,9 @@ out:
> > > >            }
> > > >            migrate_fd_error(s, local_err);
> > > >            error_propagate(errp, local_err);
> > > > +        if (stopped && runstate_is_live(s->vm_old_state)) {
> > > > +            vm_start();
> > > > +        }
> > >
> > > What about non-live states? Shouldn't this be:
> > >
> > > if (stopped) {
> > >      vm_resume();
> > > }
> >
> > Not quite.  vm_old_state may be a stopped state, so we don't want to resume.
> > However, I should probably restore the old stopped state here.  I'll try some 
> > more
> > error recovery scenarios.
>
> AIUI vm_resume() does the right thing already:
>
> void vm_resume(RunState state)
> {
>      if (runstate_is_live(state)) {
>          vm_start();
>      } else {
>          runstate_set(state);
>      }
> }

Yes, thanks, I do need to set vm_old_state if not live.  It should be:

out:
    ...
    if (stopped) {
        vm_resume(s->vm_old_state);
    }

- Steve

> > > >            return;
> > > >        }
> > > >    }
> > > > @@ -3738,7 +3751,6 @@ void migrate_fd_connect(MigrationState *s, Error 
> > > > *error_in)
> > > >        Error *local_err = NULL;
> > > >        uint64_t rate_limit;
> > > >        bool resume = (s->state == MIGRATION_STATUS_POSTCOPY_RECOVER_SETUP);
> > > > -    int ret;
> > > >    
> > > >        /*
> > > >         * If there's a previous error, free it and prepare for another one.
> > > > @@ -3810,14 +3822,6 @@ void migrate_fd_connect(MigrationState *s, Error 
> > > > *error_in)
> > > >            return;
> > > >        }
> > > >    
> > > > -    if (migrate_mode_is_cpr(s)) {
> > > > -        ret = migration_stop_vm(s, RUN_STATE_FINISH_MIGRATE);
> > > > -        if (ret < 0) {
> > > > -            error_setg(&local_err, "migration_stop_vm failed, error %d", -ret);
> > > > -            goto fail;
> > > > -        }
> > > > -    }
> > > > -
> > > >        if (migrate_background_snapshot()) {
> > > >            qemu_thread_create(&s->thread, "mig/snapshot",
> > > >                    bg_migration_thread, s, QEMU_THREAD_JOINABLE);