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Re: [Qemu-devel] [PATCH] hw/arm/bcm283x: Fix crash with device_add bcm28

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH] hw/arm/bcm283x: Fix crash with device_add bcm2837 on unsupported machines
Date: Thu, 12 Jul 2018 10:04:48 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0

On 11/07/2018 21:59, Eduardo Habkost wrote:
> What exactly guarantees there will be no other references to
> (e.g.) `&s->control` when `s` is freed?
> We know the references added by object_initialize(),
> object_property_add_child() and qdev_set_parent_bus() will be
> dropped, but what about other code calling object_ref()?

That would be a bug.  This is in fact the reason why
memory_region_ref/unref exists---to take the reference on the "outer"
device object rather than the contained memory region object.  It's not
pretty though.

I've thought of generalizing the pattern to Object (object_ref adds a
reference to the container rather than the contained object, and
finalize takes care of finalizing the contained object too), but I'm a
bit wary of doing it since it would complicate things further and
(except for MemoryRegions) it hasn't been a problem in practice.


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