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Re: [Qemu-ppc] [Qemu-devel] [PATCH v4 6/7] qdev: Protect device-list-pro

From: Markus Armbruster
Subject: Re: [Qemu-ppc] [Qemu-devel] [PATCH v4 6/7] qdev: Protect device-list-properties against broken devices
Date: Thu, 01 Oct 2015 07:45:45 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

Andreas Färber <address@hidden> writes:

> Am 28.09.2015 um 22:08 schrieb Markus Armbruster:
>> Several devices don't survive object_unref(object_new(T)): they crash
>> or hang during cleanup, or they leave dangling pointers behind.
>> This breaks at least device-list-properties, because
>> qmp_device_list_properties() needs to create a device to find its
>> properties.  Broken in commit f4eb32b "qmp: show QOM properties in
>> device-list-properties", v2.1.  Example reproducer:
>>     $ qemu-system-aarch64 -nodefaults -display none -machine none -S
>> -qmp stdio
>>     {"QMP": {"version": {"qemu": {"micro": 50, "minor": 4, "major":
>> 2}, "package": ""}, "capabilities": []}}
>>     { "execute": "qmp_capabilities" }
>>     {"return": {}}
>>     { "execute": "device-list-properties", "arguments": {
>> "typename": "pxa2xx-pcmcia" } }
>>     qemu-system-aarch64: /home/armbru/work/qemu/memory.c:1307:
>> memory_region_finalize: Assertion `((&mr->subregions)->tqh_first ==
>> ((void *)0))' failed.
>>     Aborted (core dumped)
>>     [Exit 134 (SIGABRT)]
>> Unfortunately, I can't fix the problems in these devices right now.
>> Instead, add DeviceClass member cannot_even_create_with_object_new_yet
>> to mark them:
> This name is very misleading unfortunately. You must be able to create
> any QOM object with object_new(), you just can't clean them up IIUC.

Fair enough.  Initially, I had crashes in object_new(), too, but they
eventually turned out to be innocent victims of prior memory corruption.

> What about cannot_clean_up_with_finalize_yet or irreversible_to_create?

I'll use the former or something very similar.

> ACK for the general approach of adding a new ugly field. ;)


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