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

[Stefan Hajnoczi]

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, you
need to audit virtio-pci and virtio-net to make sure all resources and
qdev properties are freed once and only once.

In the case of virtio-net, the qdev properties are duplicated so both
virtio-net-pci and virtio-net point qdev properties at the same fields
in virtio-net.  For example, the "tx" string property will be
double-freed with your patch.

You can use the alias properties that I introduced to avoid duplicating
qdev properties for virtio-net.

Stefan

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