Re: [PATCH 1/2] virtio_balloon: factor out virtballoon_quiesce()

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jun 22, 2026 at 04:46:48PM +0200, David Hildenbrand (Arm) wrote:
> On 6/22/26 15:37, Denis V. Lunev wrote:
> > virtballoon_remove() stops all of the balloon's asynchronous work (the
> > free page reporting worker, the inflate/deflate and stats workers, the
> > OOM notifier and the free page shrinker) before tearing the device
> > down. A following change needs the same teardown from a .shutdown
> > handler, so move it into a virtballoon_quiesce() helper.
> > 
> > No functional change.
> > 
> > Signed-off-by: Denis V. Lunev <den@openvz.org>
> > ---
> >  drivers/virtio/virtio_balloon.c | 27 ++++++++++++++++++++-------
> >  1 file changed, 20 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> > index 088b3a0e6ce6..5b02d9191ac6 100644
> > --- a/drivers/virtio/virtio_balloon.c
> > +++ b/drivers/virtio/virtio_balloon.c
> > @@ -1098,26 +1098,39 @@ static void remove_common(struct virtio_balloon *vb)
> >  	vb->vdev->config->del_vqs(vb->vdev);
> >  }
> >  
> > -static void virtballoon_remove(struct virtio_device *vdev)
> > +/*
> > + * Stop all asynchronous balloon work. The device must still be alive so that
> > + * in-flight requests can drain via the host before it is reset or freed.
> > + */
> > +static void virtballoon_quiesce(struct virtio_balloon *vb)
> >  {
> > -	struct virtio_balloon *vb = vdev->priv;
> > +	struct virtio_device *vdev = vb->vdev;
> >  
> > -	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING))
> > +	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_REPORTING))
> >  		page_reporting_unregister(&vb->pr_dev_info);
> 
> Most functions here grab mutexes and can sleep. I assume that's fine in shutdown
> context.
> 
> Nothing jumped at me
> 
> 
> Sashiko asks whether ->remove (hotunplug/driver-unloading) can follow a
> ->shutdown callback. I don't know, seems questionable if this could happen and
> should probably be handled by the core?
> 
> If it's possible you'd have to remember that stuff was already quiesce'ed. Maybe
> simply by checking early in virtballoon_quiesce() whether vb->stop_update ==
> true already.
> 
> -- 
> Cheers,
> 
> David

I don't think it can happen.

-- 
MST