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

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Message-ID: <CAM9d7cg56onNLfpUwMDDJaMpJiYpwgk=UT7jFF5rhH0U2dH-Pw@mail.gmail.com>
Date:   Wed, 9 Feb 2022 11:28:50 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        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>,
        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,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH 05/12] drm/i915: Protect lockdep functions with #ifdef

Hello,

On Wed, Feb 9, 2022 at 8:27 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Wed, 09 Feb 2022 15:49:01 +0200
> Jani Nikula <jani.nikula@...ux.intel.com> wrote:
>
> > > 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.

Because work_struct.lockdep_map is there only if CONFIG_LOCKDEP=y.

>
> I addressed this already. I suggested to add a "raw" variant that turns to
> a nop when LOCKDEP is not enabled. That is, for those locations that are
> only for working with LOCKDEP, the call will be:
>
>         lockdep_init_map_raw()
>
> This will differentiate the locations that are for just lockdep and those
> that are for both lockdep and tracing.

Yep, this should be fine if it's actually defined on CONFIG_LOCKDEP=y.

Thanks,
Namhyung