Re: [PATCH v4 13/25] virtio_console: enable VQs early

Michael S. Tsirkin
2014-10-20T14:04:11Z

On Mon, Oct 20, 2014 at 04:35:55PM +0300, Michael S. Tsirkin wrote:
> On Mon, Oct 20, 2014 at 02:42:23PM +0200, Cornelia Huck wrote:
> > On Mon, 20 Oct 2014 13:07:50 +0100
> > Thomas Graf <tgraf@suug.ch> wrote:
> >
> > > On 10/13/14 at 10:50am, Michael S. Tsirkin wrote:
> > > > virtio spec requires drivers to set DRIVER_OK before using VQs.
> > > > This is set automatically after probe returns, virtio console violated this
> > > > rule by adding inbufs, which causes the VQ to be used directly within
> > > > probe.
> > > >
> > > > To fix, call virtio_device_ready before using VQs.
> > > >
> > > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > > ---
> > > > drivers/char/virtio_console.c | 2 ++
> > > > 1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> > > > index b585b47..6ebe8f6 100644
> > > > --- a/drivers/char/virtio_console.c
> > > > +++ b/drivers/char/virtio_console.c
> > > > @@ -1449,6 +1449,8 @@ static int add_port(struct ports_device *portdev, u32 id)
> > > > spin_lock_init(&port->outvq_lock);
> > > > init_waitqueue_head(&port->waitqueue);
> > > >
> > > > + virtio_device_ready(portdev->vdev);
> > > > +
> > > > /* Fill the in_vq with buffers so the host can send us data. */
> > > > nr_added_bufs = fill_queue(port->in_vq, &port->inbuf_lock);
> > > > if (!nr_added_bufs) {
> > >
> > > Seems like probe and add_port() now both set VIRTIO_CONFIG_S_DRIVER_OK
> >
> > I think we need to set this in the probe function instead, otherwise we
> > fail for multiqueue (which also wants to use the control queue early).
> >
> > Completely untested patch below; I can send this with proper s-o-b if
> > it helps.
> >
> > diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> > index bfa6400..cf7a561 100644
> > --- a/drivers/char/virtio_console.c
> > +++ b/drivers/char/virtio_console.c
> > @@ -1449,8 +1449,6 @@ static int add_port(struct ports_device *portdev, u32 id)
> > spin_lock_init(&port->outvq_lock);
> > init_waitqueue_head(&port->waitqueue);
> >
> > - virtio_device_ready(portdev->vdev);
> > -
> > /* Fill the in_vq with buffers so the host can send us data. */
> > nr_added_bufs = fill_queue(port->in_vq, &port->inbuf_lock);
> > if (!nr_added_bufs) {
> > @@ -2026,6 +2024,8 @@ static int virtcons_probe(struct virtio_device *vdev)
> > spin_lock_init(&portdev->ports_lock);
> > INIT_LIST_HEAD(&portdev->ports);
> >
> > + virtio_device_ready(portdev->vdev);
> > +
> > if (multiport) {
> > unsigned int nr_added_bufs;
> >
>
> I wanted to set DRIVER_OK as late as possible, to both reduce
> the chance it can fail after DRIVER_OK and to reduce the risk of
> introducing a regression since old qemu might only start sending
> interrupts after DRIVER_OK is set.
>
> So I wanted everything completely initialized before DRIVER_OK.
>
> You patch makes sense to me since nothing can fail,
> and we won't get interrupts before we add inbufs.
>
> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
>
> Testig will report shortly, pls send with sob line.

Sure enough, this helps:

Tested-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>

Pls repost as a top-level patch.

> --
> MST