QEMU device refcounting when device creates a container MR

[Peter Maydell <peter.maydell@linaro.org>]

Hi; does anybody know how device reference counting is supposed
to work when the device creates a "container" MemoryRegion which
it then puts some of its own subregions in to?

As far as I can see when you do memory_region_add_subregion it
increases the refcount on the owner of the subregion. So if a
device creates a container MR in its own init or realize method
and adds sub-MRs that it owns to that container, this increases
the refcount on the device permanently, and so the device won't
ever be deinited.

As a specific example, the usb-chipidea device does this in its
init method, so if you run the arm device-introspect-test under
leak-sanitizer it complains about a memory leak that happens
when the device is put through the "init-introspect-deref" cycle.

-- PMM