On 2025/09/17 20:57, Daniel P. Berrangé wrote:
On Wed, Sep 17, 2025 at 07:13:25PM +0900, Akihiko Odaki wrote:
Based-on: <cover.1751493467.git.bala...@eik.bme.hu>
("[PATCH v2 00/14] hw/pci-host/raven clean ups")
Supersedes: <20240829-memory-v1-1-ac07af2f4...@daynix.com>
("[PATCH] docs/devel: Prohibit calling object_unparent() for memory region")
Children are automatically unparented so manually unparenting is
unnecessary.
Where is automatic unparenting you're referring to being done ?
Worse, automatic unparenting happens before the instance_finalize()
callback of the parent gets called, so object_unparent() calls in
the callback will refer to objects that are already unparented, which
is semantically incorrect.
IIUC, object_property_add_child will acquire a reference on
the child, and object_property_del_child (and thus
object_unparent) will release that reference.
The 'object_finalize' method, and thus 'instance_finalize'
callback, won't be invoked until the last reference is
dropped on the object in question.
IOW, it should be impossible for 'object_finalize' to ever
run, as long as the child has a parent set.
So if we're in the 'finalize' then 'object_unparent' must
be a no-op as the child must already have no references
held and thus no parent.
IOW, the reason to remove 'object_unparent' calls from
finalize is surely because they do nothing at all,
rather than this talk about callbacks being run at the
wrong time ?
This patch series deals with the situation where the parent calls
object_unparent() in its instance_finalize() callback. The process of
finalization looks like as follows:
1. The parent's reference count reaches to zero. Please note that there
can be remaining children that are referenced by the parent at this point.
2. object_finalize() is called.
2a. object_property_del_all() is called and the parent releases
references to its children. This is what I referred as "automatic
unparenting". The children without any other references will be
finalized here.
2b. instance_finalize() is called. Past children may be already
finalized, and calling object_unparent() here will cause dereferencing
finalized objects in that case, which should be avoided.
Regards,
Akihiko Odaki
