Re: [Qemu-devel] [PATCH 5/7] qdev: Protect device-list-properties against broken devices

[Eduardo Habkost]

On Fri, Sep 18, 2015 at 02:00:38PM +0200, Markus Armbruster wrote:
> 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:
> 
> * Crash or hang during cleanup (didn't debug them, so I can't say
>   why): "pxa2xx-pcmcia", "realview_pci", "versatile_pci",
>   "s390-sclp-event-facility", "sclp"
> 
> * Dangling pointers: all CPUs, plus "allwinner-a10", "digic",
>   "fsl,imx25", "fsl,imx31", "xlnx,zynqmp", because they create CPUs

That's isn't true for all CPU classes, only the ones that (incorrectly)
call cpu_exec_init() on instance_init instead of realize. I believe at
least TYPE_POWERPC_CPU is safe already.

-- 
Eduardo