Re: [Qemu-devel] [PATCH v2 01/16] qom/object: Add a new function object_initialize_child()

[Eduardo Habkost <ehabkost@redhat.com>]

On Thu, Aug 16, 2018 at 01:59:49PM +0200, Thomas Huth wrote:
> On 07/14/2018 12:57 AM, Eduardo Habkost wrote:
> > On Fri, Jul 13, 2018 at 10:27:29AM +0200, Thomas Huth wrote:
> >> A lot of code is using the object_initialize() function followed by a call
> >> to object_property_add_child() to add the newly initialized object as a child
> >> of the current object. Both functions increase the reference counter of the
> >> new object, but many spots that call these two functions then forget to drop
> >> one of the superfluous references. So the newly created object is often not
> >> cleaned up correctly when the parent is destroyed. In the worst case, this
> >> can cause crashes, e.g. because device objects are not correctly removed from
> >> their parent_bus.
> >>
> >> Since this is a common pattern between many code spots, let's introdcue a
> >> new function that takes care of calling all three required initialization
> >> functions, first object_initialize(), then object_property_add_child() and
> >> finally object_unref().
> >>
> >> And while we're at object.h, also fix some copy-n-paste errors in the
> >> comments there ("to store the area" --> "to store the error").
> >>
> >> Signed-off-by: Thomas Huth <thuth@redhat.com>
> > 
> > Potential candidates for using the new function, found using the
> > following Coccinelle patch:
> > 
> > @@
> > expression child, size, type, parent, errp, propname;
> > @@
> > -object_initialize(child, size, type);
> > -object_property_add_child(
> > +object_initialize_child(
> >                            parent, propname, 
> > -                          OBJECT(child),
> > +                          child, size, type,
> >                            errp);
> > 
> > Some of them (very few) already call object_unref() and need to
> > be fixed manually.
> > 
> > Most of the remaining ~50 object_initialize() callers are also
> > candidates, even if they don't call object_property_add_child()
> > today.
> > 
> > Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> 
> Care to turn this into a proper patch, now that we left the freeze period?

It's possible, but we need a volunteer to review each hunk
because the existing code might be (correctly) calling
object_unref() (either immediately or when parent is finalized).

I will keep this in my TODO list, but it's not my top priority
right now.

-- 
Eduardo