linux-kernel - Re: linux-next: build failure after merge of the nvdimm tree

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Message-ID: <CAOSf1CGjFOPPQPYNA=uLFJnVyNXQnsoBb8rm2qFi8uuUHmw8ZA@mail.gmail.com>
Date:   Mon, 9 Apr 2018 17:34:03 +1000
From:   Oliver <oohall@...il.com>
To:     Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Device Tree <devicetree@...r.kernel.org>,
        Rob Herring <robh@...nel.org>
Subject: Re: linux-next: build failure after merge of the nvdimm tree

On Mon, Apr 9, 2018 at 1:38 PM, Oliver <oohall@...il.com> wrote:
> On Mon, Apr 9, 2018 at 1:16 PM, Stephen Rothwell <sfr@...b.auug.org.au> wrote:
>> Hi Dan,
>>
>> After merging the nvdimm tree, today's linux-next build (x86_64
>> allmodconfig) failed like this:
>>
>> ERROR: "of_node_to_nid" [drivers/nvdimm/of_pmem.ko] undefined!
>>
>> Caused by commit
>>
>>   717197608952 ("libnvdimm: Add device-tree based driver")
>>
>> X86 seems to not have a version of of_node_to_nid() even though CONFIG_OF
>> and CONFIG_NUMA are both 'y' in this build.
>
> It's a side effect of a driver selecting CONFIG_OF accidently. There's
> a patch to fix this in the drm-misc-next tree:
>
> https://lkml.org/lkml/2018/4/3/17
>
>> I have used the nvdimm tree from next-20180406 for today.
>
> That works too.

Hmm, on closer inspection this is actually a bug in the of driver. The
patch above fixes the specific problem that we hit on ia64 due to
CONFIG_OF being selected by accident, but the underlying issue will
affect any platform that doesn't provide an implementation of
of_node_to_nid().

The fundamental problem is that the various actual implementations of
of_node_to_nid (ppc, sparc and the generic one in of_numa.c) export
the symbol. While the fallback implementation does not because it is
defined as a weak symbol. As a result we'll get this build failure iff
there's a call to of_node_to_nid() in a module.

The one-line fix is just to delete the call to of_node_to_nid() in
of_pmem.c. I have a patch that adds a Kconfig options and removes the
weak symbol games. That needs Acks from the ppc, sparc and DT
maintainers though so it'll take longer to organise.

Oliver