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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 4 Dec 2023 07:19:26 +0900
Message-ID: <CAHk-=wiS6nyWNjaTW_XL1ec3+-=tOszj+_sWGfPv9RG5WX5isQ@mail.gmail.com>
Subject: Re: [PATCH -tip 1/3] x86/percpu: Fix "const_pcpu_hot" version
 generation failure
To:     Uros Bizjak <ubizjak@gmail.com>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org,
        Andy Lutomirski <luto@kernel.org>,
        Brian Gerst <brgerst@gmail.com>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Ingo Molnar <mingo@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Josh Poimboeuf <jpoimboe@redhat.com>
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On Mon, 4 Dec 2023 at 07:12, Uros Bizjak <ubizjak@gmail.com> wrote:
>
> +/*
> + * The generic per-cpu infrastrucutre is not suitable for
> + * reading const-qualified variables.
> + */
> +#define this_cpu_read_const(pcp)       ({ BUG(); (typeof(pcp))0; })

NAK. Absolutely not.

No way in hell is it acceptable to make this a run-time BUG. If it
doesn't work, it needs to be a compile failure. End of story.

                Linus