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

[Pino Toscano]

On Friday, 21 October 2016 16:20:30 CEST Eric Blake wrote:
> 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. :(

Funny, now I cannot either, not even by resetting master back to the day
when I did the patches.  And I'm pretty sure that it was an issue, since
doing only this patch did not fully fix the leak: valgrind runs were
fine, so a full run of the libguestfs test suite with the rebuild qemu
as hypervisor.

> > 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.

I agree on the "this is not needed part", so let's just drop this patch.

Thanks,
-- 
Pino Toscano

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