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Subject: Re: [mainline][DLPAR][Oops] OF: ERROR: Bad of_node_put() on /cpus
To: Michael Ellerman <mpe@ellerman.id.au>, Rob Herring <robh@kernel.org>,
        abdul <abdhalee@linux.vnet.ibm.com>
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From: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Date: Thu, 21 Sep 2017 11:48:22 -0700
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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.

-Tyrel

> 
> I've updated my test script to do roughly $(nproc) x 10 DLPAR removes,
> which is hopefully sufficient to catch these bugs in future.
> 
> cheers
>