Re: [PATCH net] vsock/virtio: enable VQs early on probe

[Stefano Garzarella]

On Tue, Mar 22, 2022 at 09:36:14AM -0400, Michael S. Tsirkin wrote:
> On Tue, Mar 22, 2022 at 11:38:23AM +0100, Stefano Garzarella wrote:
> > virtio spec requires drivers to set DRIVER_OK before using VQs.
> > This is set automatically after probe returns, but virtio-vsock
> > driver uses VQs in the probe function to fill rx and event VQs
> > with new buffers.
>
>
> So this is a spec violation. absolutely.
>
> > Let's fix this, calling virtio_device_ready() before using VQs
> > in the probe function.
> >
> > Fixes: 0ea9e1d3a9e3 ("VSOCK: Introduce virtio_transport.ko")
> > Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> > ---
> >  net/vmw_vsock/virtio_transport.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> > index 5afc194a58bb..b1962f8cd502 100644
> > --- a/net/vmw_vsock/virtio_transport.c
> > +++ b/net/vmw_vsock/virtio_transport.c
> > @@ -622,6 +622,8 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
> >  	INIT_WORK(&vsock->event_work, virtio_transport_event_work);
> >  	INIT_WORK(&vsock->send_pkt_work, virtio_transport_send_pkt_work);
> >
> > +	virtio_device_ready(vdev);
> > +
> >  	mutex_lock(&vsock->tx_lock);
> >  	vsock->tx_run = true;
> >  	mutex_unlock(&vsock->tx_lock);
>
> Here's the whole code snippet:
>
>
>        mutex_lock(&vsock->tx_lock);
>        vsock->tx_run = true;
>        mutex_unlock(&vsock->tx_lock);
>
>        mutex_lock(&vsock->rx_lock);
>        virtio_vsock_rx_fill(vsock);
>        vsock->rx_run = true;
>        mutex_unlock(&vsock->rx_lock);
>
>        mutex_lock(&vsock->event_lock);
>        virtio_vsock_event_fill(vsock);
>        vsock->event_run = true;
>        mutex_unlock(&vsock->event_lock);
>
>        if (virtio_has_feature(vdev, VIRTIO_VSOCK_F_SEQPACKET))
>                vsock->seqpacket_allow = true;
>
>        vdev->priv = vsock;
>        rcu_assign_pointer(the_virtio_vsock, vsock);
>
>        mutex_unlock(&the_virtio_vsock_mutex);
>
>
> I worry that this is not the only problem here:
> seqpacket_allow and setting of vdev->priv at least after
> device is active look suspicious.

Right, so if you agree I'll move these before virtio_device_ready().

> E.g.:
>
> static void virtio_vsock_event_done(struct virtqueue *vq)
> {
>        struct virtio_vsock *vsock = vq->vdev->priv;
>
>        if (!vsock)
>                return;
>        queue_work(virtio_vsock_workqueue, &vsock->event_work);
> }
>
> looks like it will miss events now they will be reported earlier.
> One might say that since vq has been kicked it might send
> interrupts earlier too so not a new problem, but
> there's a chance device actually waits until DRIVER_OK
> to start operating.

Yes I see, should I break into 2 patches (one where I move the code 
already present and this one)?

Maybe a single patch is fine since it's the complete solution.

Thank you for the detailed explanation,
Stefano