Re: [Qemu-devel] commit da57febfed "qdev: give all devices a canonical path" broke usb_del

[Anthony Liguori <aliguori@us.ibm.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> Il 20/08/2012 19:58, Anthony Liguori ha scritto:
>> Michael Tokarev <mjt@tls.msk.ru> writes:
>> 
>>> On 08.08.2012 17:09, Michael Tokarev wrote:
>>> []
>>>> Something similar should be applied to 1.1-stable.  FWIW, some
>>>> changes are not needed there.
>>>
>>> Cherry-pick to stable-1.1 removes the two unneeded hunks.
>>> This is what I plan to include into debian package.  It
>>> fixes the original usb_del issue, and I didn't find new
>>> regressions so far - tried a few device_del and similar.
>>>
>>> Should it go to qemu/stable-1.1 as well?
>>>
>>> Thank you!
>>>
>>> /mjtAuthor: Paolo Bonzini <pbonzini@redhat.com>
>>> Date:   Wed Aug 8 14:39:11 2012 +0200
>>> Bug-Debian: http://bugs.debian.org/684282
>>> Comment: cherry-picked from qemu/master to stable-1.1 (mjt)
>>>
>>>     qom: object_delete should unparent the object first
>>>     
>>>     object_deinit is only called when the reference count goes to zero,
>>>     and yet tries to do an object_unparent.  Now, object_unparent
>>>     either does nothing or it will decrease the reference count.
>>>     Because we know the reference count is zero, the object_unparent
>>>     call in object_deinit is useless.
>>>     
>>>     Instead, we need to disconnect the object from its parent just
>>>     before we remove the last reference apart from the parent's.  This
>>>     happens in object_delete.  Once we do this, all calls to
>>>     object_unparent peppered through QEMU can go away.
>>>     
>>>     Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>>>     Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
>>>
>>> diff --git a/hw/acpi_piix4.c b/hw/acpi_piix4.c
>>> index 0345490..585da4e 100644
>>> --- a/hw/acpi_piix4.c
>>> +++ b/hw/acpi_piix4.c
>>> @@ -299,7 +299,6 @@ static void acpi_piix_eject_slot(PIIX4PMState *s, unsigned slots)
>>>              if (pc->no_hotplug) {
>>>                  slot_free = false;
>>>              } else {
>>> -                object_unparent(OBJECT(dev));
>>>                  qdev_free(qdev);
>>>              }
>>>          }
>>> diff --git a/hw/qdev.c b/hw/qdev.c
>>> index 6a8f6bd..9bb1c6b 100644
>>> --- a/hw/qdev.c
>>> +++ b/hw/qdev.c
>>> @@ -240,7 +240,6 @@ void qbus_reset_all_fn(void *opaque)
>>>  int qdev_simple_unplug_cb(DeviceState *dev)
>>>  {
>>>      /* just zap it */
>>> -    object_unparent(OBJECT(dev));
>>>      qdev_free(dev);
>>>      return 0;
>>>  }
>>> diff --git a/hw/xen_platform.c b/hw/xen_platform.c
>>> index 0214f37..84221df 100644
>>> --- a/hw/xen_platform.c
>>> +++ b/hw/xen_platform.c
>>> @@ -87,9 +87,6 @@ static void unplug_nic(PCIBus *b, PCIDevice *d)
>>>  {
>>>      if (pci_get_word(d->config + PCI_CLASS_DEVICE) ==
>>>              PCI_CLASS_NETWORK_ETHERNET) {
>>> -        /* Until qdev_free includes a call to object_unparent, we call it here
>>> -         */
>>> -        object_unparent(&d->qdev.parent_obj);
>>>          qdev_free(&d->qdev);
>>>      }
>>>  }
>>> diff --git a/qom/object.c b/qom/object.c
>>> index 6f839ad..58dd886 100644
>>> --- a/qom/object.c
>>> +++ b/qom/object.c
>>> @@ -347,8 +347,6 @@ static void object_deinit(Object *obj, TypeImpl *type)
>>>      if (type_has_parent(type)) {
>>>          object_deinit(obj, type_get_parent(type));
>>>      }
>>> -
>>> -    object_unparent(obj);
>>>  }
>>>  
>>>  void object_finalize(void *data)
>>> @@ -385,8 +383,9 @@ Object *object_new(const char *typename)
>>>  
>>>  void object_delete(Object *obj)
>>>  {
>>> +    object_unparent(obj);
>>> +    g_assert(obj->ref == 1);
>>>      object_unref(obj);
>>> -    g_assert(obj->ref == 0);
>>>      g_free(obj);
>>>  }
>> 
>> This won't work with composition.  object_delete() is never called for
>> child<> objects.
>
> For non-heap-allocated children, their last ref will go away when the
> parent's child<> property is eliminated.  This will remove the last
> reference and call object_finalize (which will take care of multiple
> levels of compositions).
>
> The same holds for heap-allocated children, but indeed you will leak the
> memory for the object because object_delete is not called.  However this
> is already the case, the patch is not introducing a regression.

Ok, can you submit as a top level patch and I'll apply it for 1.2?

Regards,

Anthony Liguori

>
> Paolo