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

[Eduardo Habkost]

On Fri, Sep 18, 2015 at 08:42:54PM +0200, Thomas Huth wrote:
> On 18/09/15 14:00, 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
> > 
> > * Assert kvm_enabled(): "host-x86_64-cpu", host-i386-cpu",
> >   "host-powerpc64-cpu", "host-embedded-powerpc-cpu",
> >   "host-powerpc-cpu"
> 
> I just had a look at the powerpc code - you're likely talking about
> the "assert(kvm_enabled());" in the kvmppc_host_cpu_initfn() in
> target-ppc/kvm.c ? That should be fine, I think, because
> kvm_ppc_register_host_cpu_type() is only done on ppc when KVM has been
> enabled.

It's true that currently the assert() will never trigger, but we will
have to eventually move class registration to type_init if we want to
make a generic query-cpu-definitions implementation work properly
without depending on global machine accel configuration.

It won't hurt to set cannot_even_create_with_object_new_yet properly to
reflect that the class isn't ready yet.

-- 
Eduardo