Re: [Qemu-devel] [PATCH v2] virtio: Move memory_listener_unregister to .unrealize

[Fam Zheng <famz@redhat.com>]

On Wed, 05/17 02:58, Paolo Bonzini wrote:
> The child property is deleted when bus_unparent calls object_unparent:
> 
>     while ((kid = QTAILQ_FIRST(&bus->children)) != NULL) {
>         DeviceState *dev = kid->child;
>         object_unparent(OBJECT(dev));
>     }
> 
> and in turn bus_unparent is called by the VirtIOSCSIPCI's unparent
> callback (device_unparent):
> 
>     while (dev->num_child_bus) {
>         bus = QLIST_FIRST(&dev->child_bus);
>         object_unparent(OBJECT(bus));
>     }

OK, sorry for being dumb, these are way over my head. Let me try again:

I count three references before unplug:

a.1) object_property_add_child in virtio_instance_init_common as virtio-backend
a.2) qdev_set_parent_bus in virtio_scsi_pci_realize by virtio-pci-bus
a.3) qbus_set_hotplug_handler in virtio_scsi_device_realize for 

Only two object_unref()'s happen in unplug, respectively:

b.1) object_finalize_child_property, matches a.1)
b.2) bus_remove_child, matches a.2)

Do we need cleanup for a.3) ? The patch below does fix the crash for me.

---

diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index 46a3e3f..fde1b1fe 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -918,6 +918,8 @@ void virtio_scsi_common_unrealize(DeviceState *dev, Error **errp)
 
 static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
 {
+    VirtIOSCSI *s = VIRTIO_SCSI(dev);
+    qbus_set_hotplug_handler(BUS(&s->bus), NULL, &error_abort);
     virtio_scsi_common_unrealize(dev, errp);
 }