Linux Virtualization - Mar 2015 - [PATCH] virtio_balloon: set DRIVER_OK before using device

virtio spec requires that all drivers set DRIVER_OK
before using devices. While balloon isn't yet
included in the virtio 1 spec, previous spec versions
also required this.

virtio balloon might violate this rule: probe calls
kthread_run before setting DRIVER_OK, which might run
immediately and cause balloon to inflate/deflate.

To fix, call virtio_device_ready before running the kthread.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 drivers/virtio/virtio_balloon.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 5a6ad6d..6a356e3 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -508,6 +508,8 @@ static int virtballoon_probe(struct virtio_device *vdev)
 	if (err < 0)
 		goto out_oom_notify;
 
+	virtio_device_ready(vdev);
+
 	vb->thread = kthread_run(balloon, vb, "vballoon");
 	if (IS_ERR(vb->thread)) {
 		err = PTR_ERR(vb->thread);
-- 
MST

"Michael S. Tsirkin" <mst at redhat.com>
writes:
> virtio spec requires that all drivers set DRIVER_OK
> before using devices. While balloon isn't yet
> included in the virtio 1 spec, previous spec versions
> also required this.
>
> virtio balloon might violate this rule: probe calls
> kthread_run before setting DRIVER_OK, which might run
> immediately and cause balloon to inflate/deflate.
>
> To fix, call virtio_device_ready before running the kthread.
>
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Replied, CC'd stable.

Thanks,
Rusty.

> ---
>  drivers/virtio/virtio_balloon.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/virtio/virtio_balloon.c
b/drivers/virtio/virtio_balloon.c
> index 5a6ad6d..6a356e3 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -508,6 +508,8 @@ static int virtballoon_probe(struct virtio_device
*vdev)
>  	if (err < 0)
>  		goto out_oom_notify;
>  
> +	virtio_device_ready(vdev);
> +
>  	vb->thread = kthread_run(balloon, vb, "vballoon");
>  	if (IS_ERR(vb->thread)) {
>  		err = PTR_ERR(vb->thread);
> -- 
> MST

On Thu, Mar 05, 2015 at 01:24:47PM +1030, Rusty Russell
wrote:
> "Michael S. Tsirkin" <mst at redhat.com> writes:
> > virtio spec requires that all drivers set DRIVER_OK
> > before using devices. While balloon isn't yet
> > included in the virtio 1 spec, previous spec versions
> > also required this.
> >
> > virtio balloon might violate this rule: probe calls
> > kthread_run before setting DRIVER_OK, which might run
> > immediately and cause balloon to inflate/deflate.
> >
> > To fix, call virtio_device_ready before running the kthread.
> >
> > Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> 
> Replied, CC'd stable.
Did you mean applied?
> Thanks,
> Rusty.
> 
> 
> > ---
> >  drivers/virtio/virtio_balloon.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/virtio/virtio_balloon.c
b/drivers/virtio/virtio_balloon.c
> > index 5a6ad6d..6a356e3 100644
> > --- a/drivers/virtio/virtio_balloon.c
> > +++ b/drivers/virtio/virtio_balloon.c
> > @@ -508,6 +508,8 @@ static int virtballoon_probe(struct virtio_device
*vdev)
> >  	if (err < 0)
> >  		goto out_oom_notify;
> >  
> > +	virtio_device_ready(vdev);
> > +
> >  	vb->thread = kthread_run(balloon, vb, "vballoon");
> >  	if (IS_ERR(vb->thread)) {
> >  		err = PTR_ERR(vb->thread);
> > -- 
> > MST