linux-kernel - Re: [PATCH] mm/memcontrol.c: fix another unused function warning

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Date:   Tue, 1 Oct 2019 09:36:24 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Qian Cai <cai@....pw>, Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Chris Down <chris@...isdown.name>, Tejun Heo <tj@...nel.org>,
        cgroups@...r.kernel.org,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] mm/memcontrol.c: fix another unused function warning

On Tue, Oct 1, 2019 at 7:22 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> Removing the mem_cgroup_id_get() stub function introduced a new warning
> of the same kind when CONFIG_MMU is disabled:
>
> mm/memcontrol.c:4929:13: error: unused function 'mem_cgroup_id_get_many' [-Werror,-Wunused-function]
>
> Address this using a __maybe_unused annotation.
>
> Note: alternatively, this could be moved into an #ifdef block.  Marking it

Hi Arnd,
Thank you for the patch!  I would prefer to move the definition to the
correct set of #ifdef guards rather than __maybe_unused.  Maybe move
the definition of mem_cgroup_id_get_many() to just before
__mem_cgroup_clear_mc()?  I find __maybe_unused to be a code smell.

> 'static inline' would not work here as that would still produce the
> warning on clang, which only ignores unused inline functions declared
> in header files instead of .c files.
>
> Fixes: 4d0e3230a56a ("mm/memcontrol.c: fix a -Wunused-function warning")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  mm/memcontrol.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index c313c49074ca..5f9f90e3cef8 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4921,7 +4921,8 @@ static void mem_cgroup_id_remove(struct mem_cgroup *memcg)
>         }
>  }
>
> -static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n)
> +static void __maybe_unused
> +mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n)
>  {
>         refcount_add(n, &memcg->id.ref);
>  }
> --

-- 
Thanks,
~Nick Desaulniers