linux-kernel - Re: [PATCH] mm: memcontrol.c: move mem_cgroup_id_get_many under CONFIG

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Date:   Tue, 17 Dec 2019 15:09:21 +0000
From:   Chris Down <chris@...isdown.name>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Qian Cai <cai@....pw>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: memcontrol.c: move mem_cgroup_id_get_many under
 CONFIG_MMU

Michal Hocko writes:
>yes, I would just ignore this warning. Btw. it seems that this is
>enabled by default for -Wall. Is this useful for kernel builds at
>all? Does it realistically help discovering real issues? If not then
>can we simply blacklist it?

There's no way we're the first people to encounter these problems, so what did 
we do in the past when situations like this (adding a generic API which is not 
yet used by non-configurable code) came up, and in retrospect did they work 
well?

As far as I know -Wunused-function also guards against other errors, like when 
a function is prototyped but not actually defined, which might be more useful 
to know about.

(Side note: I'm moderately baffled that a tightly scoped __maybe_unused is 
considered sinister but somehow disabling -Wunused-function is on the table 
:-))