Re: [PATCH v3 11/11] virtio: balloon: Add freeze, restore handlers to support S4

Michael S. Tsirkin
2011-11-17T12:35:08Z

On Thu, Nov 17, 2011 at 05:59:20PM +0530, Amit Shah wrote:
> On (Thu) 17 Nov 2011 [14:25:08], Michael S. Tsirkin wrote:
> > On Thu, Nov 17, 2011 at 05:27:42PM +0530, Amit Shah wrote:
> > > Delete the vqs on the freeze callback to prepare for hibernation.
> > > Re-create the vqs in the restore callback to resume normal function.
> > >
> > > Signed-off-by: Amit Shah <amit.shah@redhat.com>
> > > ---
> > > drivers/virtio/virtio_balloon.c | 20 ++++++++++++++++++++
> > > 1 files changed, 20 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> > > index 1ff3cf4..90149d1 100644
> > > --- a/drivers/virtio/virtio_balloon.c
> > > +++ b/drivers/virtio/virtio_balloon.c
> > > @@ -363,6 +363,22 @@ static void __devexit virtballoon_remove(struct virtio_device *vdev)
> > > kfree(vb);
> > > }
> > >
> > > +#ifdef CONFIG_PM
> > > +static int virtballoon_freeze(struct virtio_device *vdev)
> > > +{
> > > + /* Now we reset the device so we can clean up the queues. */
> > > + vdev->config->reset(vdev);
> > > +
> >
> > This is a weird thing to do. We normally delete vqs then reset.
>
> No, all the drivers first reset, then delete.

BTW, reset does not flush callbacks at the moment.
It probably should.

> > For example, I don't know whether we guarantee what happens
> > to MSI-X vectors assigned meanwhile if you reset.
> > IIRC qemu doesn't use MSI-X for the balloon, but nothing
> > prevents it.
> >
> > > + vdev->config->del_vqs(vdev);
> >
> > What prevents requests being submitted at this point?
> > I see all kind of handling of freezing in the balloon thread ...
> > maybe that gives us some guarantees, but if yes
> > it makes sense to add a comment to point this out.
>
> Once reset, the host won't write anything to the vqs anyway..
>
> Amit

But thread might have already been scheduled, handling
previous requests.

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