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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 14 Sep 2021 08:46:54 -0700
Message-ID: <CAHk-=whLEofPLzzTKXN5etnH5WqsTPQRLVv8uQgHnx7c59omBg@mail.gmail.com>
Subject: Re: [RFC PATCH 5/8] sched: move CPU field back into thread_info if THREAD_INFO_IN_TASK=y
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Keith Packard <keithpac@amazon.com>,
        Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
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        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Paul Mackerras <paulus@samba.org>,
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        Christian Borntraeger <borntraeger@de.ibm.com>,
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On Tue, Sep 14, 2021 at 5:11 AM Ard Biesheuvel <ardb@kernel.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