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

[Stefan Hajnoczi <stefanha@redhat.com>]

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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, arei.gonglei@huawei.com wrote:
> > > From: Gonglei <arei.gonglei@huawei.com>
> > >
> > > 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 <arei.gonglei@huawei.com>
> > > ---
> > > 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.

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