Re: [PULL 30/33] migration: do not restart VM after successful snapshot-load

[Paolo Bonzini]

On 11/05/21 10:56, Dr. David Alan Gilbert wrote:
> * Paolo Bonzini (pbonzini@redhat.com) wrote:
> > The HMP loadvm code is calling load_snapshot rather than
> > qmp_snapshot_load, in order to bypass the job infrastructure.  The code
> > around it is almost the same, with one difference: hmp_loadvm is
> > restarting the VM if load_snapshot fails, qmp_snapshot_load is doing so
> > if load_snapshot succeeds.
> >
> > Fix the bug in QMP by moving the common code to load_snapshot.
>
> See my comment:
> https://lists.gnu.org/archive/html/qemu-devel/2021-05/msg01103.html
>
> but you've also lost Eric's Rb.

Sorry, I missed both replies.  As Daniel pointed out, the bug is in the 
QMP version.  Kevin has the correct fix, I'll send the cleanup of 
vm_stop/vm_start separately on top of his patch.

Paolo

> Dave
>
> > Cc: qemu-stable@nongnu.org
> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> > ---
> >   migration/savevm.c | 16 ++++++++--------
> >   monitor/hmp-cmds.c |  7 +------
> >   2 files changed, 9 insertions(+), 14 deletions(-)
> >
> > diff --git a/migration/savevm.c b/migration/savevm.c
> > index 52e2d72e4b..a899191cbf 100644
> > --- a/migration/savevm.c
> > +++ b/migration/savevm.c
> > @@ -2992,6 +2992,7 @@ bool load_snapshot(const char *name, const char *vmstate,
> >       int ret;
> >       AioContext *aio_context;
> >       MigrationIncomingState *mis = migration_incoming_get_current();
> > +    int saved_vm_running  = runstate_is_running();
> >   
> >       if (!bdrv_all_can_snapshot(has_devices, devices, errp)) {
> >           return false;
> > @@ -3024,6 +3025,8 @@ bool load_snapshot(const char *name, const char *vmstate,
> >           return false;
> >       }
> >   
> > +    vm_stop(RUN_STATE_RESTORE_VM);
> > +
> >       /*
> >        * Flush the record/replay queue. Now the VM state is going
> >        * to change. Therefore we don't need to preserve its consistency
> > @@ -3061,13 +3064,17 @@ bool load_snapshot(const char *name, const char 
> > *vmstate,
> >   
> >       if (ret < 0) {
> >           error_setg(errp, "Error %d while loading VM state", ret);
> > -        return false;
> > +        goto err_restart;
> >       }
> >   
> >       return true;
> >   
> >   err_drain:
> >       bdrv_drain_all_end();
> > +err_restart:
> > +    if (saved_vm_running) {
> > +        vm_start();
> > +    }
> >       return false;
> >   }
> >   
> > @@ -3135,17 +3142,10 @@ static void snapshot_load_job_bh(void *opaque)
> >   {
> >       Job *job = opaque;
> >       SnapshotJob *s = container_of(job, SnapshotJob, common);
> > -    int orig_vm_running;
> >   
> >       job_progress_set_remaining(&s->common, 1);
> >   
> > -    orig_vm_running = runstate_is_running();
> > -    vm_stop(RUN_STATE_RESTORE_VM);
> > -
> >       s->ret = load_snapshot(s->tag, s->vmstate, true, s->devices, s->errp);
> > -    if (s->ret && orig_vm_running) {
> > -        vm_start();
> > -    }
> >   
> >       job_progress_update(&s->common, 1);
> >   
> > diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
> > index 0ad5b77477..a39436c8cb 100644
> > --- a/monitor/hmp-cmds.c
> > +++ b/monitor/hmp-cmds.c
> > @@ -1127,15 +1127,10 @@ void hmp_balloon(Monitor *mon, const QDict *qdict)
> >   
> >   void hmp_loadvm(Monitor *mon, const QDict *qdict)
> >   {
> > -    int saved_vm_running  = runstate_is_running();
> >       const char *name = qdict_get_str(qdict, "name");
> >       Error *err = NULL;
> >   
> > -    vm_stop(RUN_STATE_RESTORE_VM);
> > -
> > -    if (!load_snapshot(name, NULL, false, NULL, &err) && saved_vm_running) {
> > -        vm_start();
> > -    }
> > +    load_snapshot(name, NULL, false, NULL, &err);
> >       hmp_handle_error(mon, err);
> >   }
> >   
> > --
> > 2.26.2