Re: [Qemu-devel] [PATCH] qapi: fix memory leak in QmpOutputVisitor

[Eric Blake]

On 10/18/2016 06:22 AM, Pino Toscano wrote:
> On Tuesday, 18 October 2016 06:13:30 CEST Eric Blake wrote:
>> On 10/18/2016 04:17 AM, Pino Toscano wrote:
>>> qmp_output_start_struct() and qmp_output_start_list() create a new
>>> QObject (QDict, QList) and push it to the stack of the QmpOutputVisitor,
>>> where it is saved as 'value'.  When freeing the iterator in
>>> qmp_output_free(), these values are never freed properly.
>>
>> Do any of the tests (perhaps run under valgrind) show this leak? If not,
>> maybe we should enhance their coverage.
> 
> Running a simple `qemu-img info file.qcow2` under valgrind was enough
> for me to show the leak.

I'm still not reproducing it. :(

> 
> In this case, another simple fix is needed to fully fix the leak:
> http://lists.nongnu.org/archive/html/qemu-devel/2016-10/msg04023.html

In fact, isn't that fix alone enough to fix the leak? The more I think
about this patch (and the thread on v2), the more I think it is too
prone to double-freeing things.

>>> +++ b/qapi/qmp-output-visitor.c
>>> @@ -220,6 +220,7 @@ static void qmp_output_free(Visitor *v)
>>>      while (!QSLIST_EMPTY(&qov->stack)) {
>>>          e = QSLIST_FIRST(&qov->stack);
>>>          QSLIST_REMOVE_HEAD(&qov->stack, node);
>>> +        qobject_decref(e->value);
>>>          g_free(e);
>>>      }
>>>  
>>>
>>
>>
> 
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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