Re: [Qemu-devel] [PULL v3 11/12] qdev: Protect device-list-properties against broken devices

[Andreas Färber]

Am 09.10.2015 um 16:36 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_destroy_with_object_finalize_yet
> to mark them:
> 
> * Hang during cleanup (didn't debug, so I can't say why):
>   "realview_pci", "versatile_pci".
> 
> * Dangling pointer in cpus: most CPUs, plus "allwinner-a10", "digic",
>   "fsl,imx25", "fsl,imx31", "xlnx,zynqmp", because they create such
>   CPUs
> 
> * Assert kvm_enabled(): "host-x86_64-cpu", host-i386-cpu",
>   "host-powerpc64-cpu", "host-embedded-powerpc-cpu",
>   "host-powerpc-cpu" (the powerpc ones can't currently reach the
>   assertion, because the CPUs are only registered when KVM is enabled,
>   but the assertion is arguably in the wrong place all the same)
> 
> Make qmp_device_list_properties() fail cleanly when the device is so
> marked.  This improves device-list-properties from "crashes, hangs or
> leaves dangling pointers behind" to "fails".  Not a complete fix, just
> a better-than-nothing work-around.  In the above reproducer,
> device-list-properties now fails with "Can't list properties of device
> 'pxa2xx-pcmcia'".
> 
> This also protects -device FOO,help, which uses the same machinery
> since commit ef52358 "qdev-monitor: include QOM properties in -device
> FOO, help output", v2.2.  Example reproducer:
> 
>     $ qemu-system-aarch64 -machine none -device pxa2xx-pcmcia,help
> 
> Before:
> 
>     qemu-system-aarch64: .../memory.c:1307: memory_region_finalize: Assertion 
> `((&mr->subregions)->tqh_first == ((void *)0))' failed.
> 
> After:
> 
>     Can't list properties of device 'pxa2xx-pcmcia'
> 
> Cc: "Andreas Färber" <address@hidden>

In case a v4 comes up, ;)

Acked-by: Andreas Färber <address@hidden>

Thanks for updating,
Andreas

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