linux-kernel - Re: [GIT PULL] locking changes for v5.18

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Date:   Tue, 22 Mar 2022 15:05:39 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] locking changes for v5.18

On Mon, Mar 21, 2022 at 4:11 AM Ingo Molnar <mingo@...nel.org> wrote:
>
> Sebastian Andrzej Siewior (2):
>       locking/local_lock: Make the empty local_lock_*() function a macro.

Grr. I noticed this too late, but this one actually breaks the build with clang.

Why?

Because it's now a macro, it doesn't use the argument at all, and you get:

    mm/page_alloc.c:131:40: error: variable 'pagesets' is not needed
and will not be emitted [-Werror,-Wunneeded-internal-declaration]
    static DEFINE_PER_CPU(struct pagesets, pagesets) = {
                                           ^

and I'm not sure why this doesn't show up with gcc, but apparently gcc
only warns about unused static functions, not unused static data.

Or maybe gcc considers it used just because somebody did a typeof on it.

I thought -tip had started checking with clang, but apparently not.

I see that the -mm tree has a fix for this, but I'm rather unhappy
that the -tip tree build checking has deteriorated so much, and clang
builds will now have a pointless build error that will cause issues
for bisect.

                   LInus