linux-kernel - Re: [PATCH 05/12] drm/i915: Protect lockdep functions with #ifdef

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Date:   Wed, 09 Feb 2022 15:49:01 +0200
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Byungchul Park <byungchul.park@....com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Radoslaw Burny <rburny@...gle.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        intel-gfx@...ts.freedesktop.org, paulmck@...nel.org
Subject: Re: [PATCH 05/12] drm/i915: Protect lockdep functions with #ifdef

On Tue, 08 Feb 2022, Namhyung Kim <namhyung@...nel.org> wrote:
> Hello,
>
> On Tue, Feb 8, 2022 at 10:51 AM Jani Nikula <jani.nikula@...ux.intel.com> wrote:
>>
>> On Tue, 08 Feb 2022, Namhyung Kim <namhyung@...nel.org> wrote:
>> > With upcoming lock tracepoints config, it'd define some of lockdep
>> > functions without enabling CONFIG_LOCKDEP actually.  The existing code
>> > assumes those functions will be removed by the preprocessor but it's
>> > not the case anymore.  Let's protect the code with #ifdef's explicitly.
>>
>> I don't understand why you can't keep the no-op stubs for
>> CONFIG_LOCKDEP=n.
>
> Because I want to use the lockdep annotation for other purposes.
> But the workqueue lockdep_map was defined under LOCKDEP
> only.  Please see the description in the cover letter.
>
> https://lore.kernel.org/all/20220208184208.79303-1-namhyung@kernel.org/

So lockdep_init_map() might still be there and build just fine for
CONFIG_LOCKDEP=n, but now we're actually required to wrap all call sites
in #ifdefs depending on the purpose? I'm not convinced yet.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center