Re: [Qemu-devel] [PATCH] virtio-pci: fix virtio-net child refcount in transports

[Gonglei]

> Subject: Re: [Qemu-devel] [PATCH] virtio-pci: fix virtio-net child refcount in
> transports
> 
> On Fri, Sep 05, 2014 at 11:46:32PM +0800, Gonglei wrote:
> > Hi,
> >
> > > Subject: Re: [Qemu-devel] [PATCH] virtio-pci: fix virtio-net child 
> > > refcount in
> > > transports
> > >
> > > On Thu, Sep 04, 2014 at 07:41:32PM +0800, address@hidden
> wrote:
> > > > From: Gonglei <address@hidden>
> > > >
> > > > object_initialize() leaves the object with a refcount of 1.
> > > > object_property_add_child() adds its own reference which is dropped
> > > > again when the property is deleted.
> > > >
> > > > The upshot of this is that we always have a refcount >= 1.  Upon hot
> > > > unplug the virtio-net child is not finalized!
> > > >
> > > > Drop our reference after the child property has been added to the
> > > > parent.
> > > >
> > > > Signed-off-by: Gonglei <address@hidden>
> > > > ---
> > > > Stefan had post virtio-blk in commit c5d49db4, but virtio-net has
> > > > the same problem. Maybe the other virtio devices have too.
> > > > ---
> > > >  hw/virtio/virtio-pci.c | 1 +
> > > >  1 file changed, 1 insertion(+)
> > > >
> > > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> > > > index ddb5da1..78dcd68 100644
> > > > --- a/hw/virtio/virtio-pci.c
> > > > +++ b/hw/virtio/virtio-pci.c
> > > > @@ -1456,6 +1456,7 @@ static void virtio_net_pci_instance_init(Object
> > > *obj)
> > > >      VirtIONetPCI *dev = VIRTIO_NET_PCI(obj);
> > > >      object_initialize(&dev->vdev, sizeof(dev->vdev),
> TYPE_VIRTIO_NET);
> > > >      object_property_add_child(obj, "virtio-backend",
> OBJECT(&dev->vdev),
> > > NULL);
> > > > +    object_unref(OBJECT(&dev->vdev));
> > > >  }
> > > >
> > > >  static const TypeInfo virtio_net_pci_info = {
> > >
> > > You just copied my commit but didn't consider all the work I did before
> > > to make virtio-blk safe.  Similar work is necessary for virtio-net.
> > >
> > > Before it is okay to finalize the virtio-net (dev->vdev) object,
> >
> > Sorry? In my case the virtio-net object will not be finalized at present
> > because its obj->ref is non-1 when we hot-unplug a virtio-net-pci device.
> 
> "Before" refers to making virtio-pci/virtio-net fixes first and then
> object_unref() second.  It does not mean "previously" here.

OK. Thanks. :)

Best regards,
-Gonglei