linux-kernel - Re: [PATCH] drm/i915: Disable -Wuninitialized for intel

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Date:   Tue, 18 Dec 2018 11:53:06 +0000
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org,
        LKML <linux-kernel@...r.kernel.org>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH] drm/i915: Disable -Wuninitialized for intel_breadcrumbs.o

Quoting Nick Desaulniers (2018-10-25 23:20:58)
> On Thu, Oct 25, 2018 at 12:36 PM Nathan Chancellor
> <natechancellor@...il.com> wrote:
> >
> > This warning is disabled by default in scripts/Makefile.extrawarn when
> > W= is not provided but this Makefile adds -Wall after this warning is
> > disabled so it shows up in the build when it shouldn't:
> >
> > In file included from drivers/gpu/drm/i915/intel_breadcrumbs.c:895:
> > drivers/gpu/drm/i915/selftests/intel_breadcrumbs.c:350:34: error:
> > variable 'wq' is uninitialized when used within its own initialization
> > [-Werror,-Wuninitialized]
> >         DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
> >                                         ^~
> > ./include/linux/wait.h:74:63: note: expanded from macro
> > 'DECLARE_WAIT_QUEUE_HEAD_ONSTACK'
> >         struct wait_queue_head name = __WAIT_QUEUE_HEAD_INIT_ONSTACK(name)
> >                                ~~~~                                  ^~~~
> > ./include/linux/wait.h:72:33: note: expanded from macro
> > '__WAIT_QUEUE_HEAD_INIT_ONSTACK'
> >         ({ init_waitqueue_head(&name); name; })
> >                                        ^~~~
> > 1 error generated.
> >
> > This warning looks to be a false positive given that init_waitqueue_head
> > initializes name before it is used. Rather than disable the warning for
> > the full folder like commit 46e2068081e9 ("drm/i915: Disable some extra
> 
> cc author/reviewer of 46e2068081e9.
> 
> I'm fine with the patch as is, unless others prefer to disable it for
> the whole subdir?  We could be playing whack-a-mole in the future
> disabling this warning for other translation units.

Yes, exactly this since the warning is generated by a core header and a
fairly common pattern its use is not restricted to any single file.
(Will not all selftests similarly explode?)

The other false-positive clang-6 gave was for local_clock_us().
Presumably that one is fixed?
-Chris