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From: Michael Ellerman <mpe@ellerman.id.au>
To: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>,
        Rob Herring <robh@kernel.org>, abdul <abdhalee@linux.vnet.ibm.com>
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        Paul Mackerras <paulus@samba.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [mainline][DLPAR][Oops] OF: ERROR: Bad of_node_put() on /cpus
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Tyrel Datwyler <tyreld@linux.vnet.ibm.com> writes:

> On 09/21/2017 02:57 AM, Michael Ellerman wrote:
>> Tyrel Datwyler <tyreld@linux.vnet.ibm.com> writes:
>>> On 09/20/2017 04:39 AM, Michael Ellerman wrote:
>>>> Rob Herring <robh@kernel.org> writes:
>
> <snip>
>
>>>>
>>>> Testing a fix, will report back.
>>>
>>> So, that patch slipped past me. Not only is the parent reference not ours to drop, but
>>> when I went and looked at dlpar_cpu_add() I also noticed that of_node_put() was done on
>>> the parent prior to the call to dlpar_attach_node(). With the addition of "parent" to the
>>> dlpar_attach_node() parameter list dlpar_cpu_add() needs to be fixed up to hold the
>>> "parent" reference until after dlpar_attach_node() returns.
>> 
>> Yep. I wrote the same patch :)
>> 
>> Rob asked me to test it, which I did, but /cpus starts out with an
>> elevated ref count, so you have to do ~30 (on my system) DLPAR removes
>> to hit the bug, which I didn't do.
>
> Yeah, there are a lot of things that grab references to /cpus. So, I had a good idea that
> I needed to loop a few times adding and removing multiple cpus to trigger the issue. Its
> also obvious when using those OF trace points I wrote a while back that refcount for /cpus
> is dropping off uncharacteristically in response to symmetrical adds/removes of cpus. I
> saw your note about getting that patchset resubmitted. I'll try and get that queued back
> up soon.

Thanks, it'd be great to get it in. I applied it from the list and used
it for testing this.

cheers