linux-kernel - Re: [RFC PATCH 5/8] sched: move CPU field back into thread_info if THREAD_INFO_IN

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Date:   Tue, 14 Sep 2021 08:46:54 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Keith Packard <keithpac@...zon.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Paul Mackerras <paulus@...ba.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-s390 <linux-s390@...r.kernel.org>
Subject: Re: [RFC PATCH 5/8] sched: move CPU field back into thread_info if THREAD_INFO_IN_TASK=y

On Tue, Sep 14, 2021 at 5:11 AM Ard Biesheuvel <ardb@...nel.org> wrote:
>
>  static inline unsigned int task_cpu(const struct task_struct *p)
>  {
>  #ifdef CONFIG_THREAD_INFO_IN_TASK
> -       return READ_ONCE(p->cpu);
> +       return READ_ONCE(p->thread_info.cpu);
>  #else
>         return READ_ONCE(task_thread_info(p)->cpu);
>  #endif

Those two lines look different, but aren't.

Please just remove the CONFIG_THREAD_INFO_IN_TASK conditional, and use

          return READ_ONCE(task_thread_info(p)->cpu);

unconditionally, which now does the right thing regardless.

             Linus