linux-kernel - Re: [PATCH] ACPI: processor: Fix build when CONFIG_ACPI

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Date:   Tue, 6 Apr 2021 15:22:00 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Stable <stable@...r.kernel.org>,
        kernel test robot <lkp@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ACPI: processor: Fix build when CONFIG_ACPI_PROCESSOR=m

On Tue, Apr 6, 2021 at 2:50 PM Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>
> Commit 8cdddd182bd7 ("ACPI: processor: Fix CPU0 wakeup in
> acpi_idle_play_dead()") tried to fix CPU0 hotplug breakage by copying
> wakeup_cpu0() + start_cpu0() logic from hlt_play_dead()//mwait_play_dead()
> into acpi_idle_play_dead(). The problem is that these functions are not
> exported to modules so when CONFIG_ACPI_PROCESSOR=m build fails.
>
> The issue could've been fixed by exporting both wakeup_cpu0()/start_cpu0()
> (the later from assembly) but it seems putting the whole pattern into a
> new function and exporting it instead is better.
>
> Reported-by: kernel test robot <lkp@...el.com>
> Fixes: 8cdddd182bd7 ("CPI: processor: Fix CPU0 wakeup in acpi_idle_play_dead()")
> Cc: <stable@...r.kernel.org> # 5.10+
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/include/asm/smp.h    |  2 +-
>  arch/x86/kernel/smpboot.c     | 15 ++++++++++-----
>  drivers/acpi/processor_idle.c |  3 +--
>  3 files changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> index 57ef2094af93..6f79deb1f970 100644
> --- a/arch/x86/include/asm/smp.h
> +++ b/arch/x86/include/asm/smp.h
> @@ -132,7 +132,7 @@ void native_play_dead(void);
>  void play_dead_common(void);
>  void wbinvd_on_cpu(int cpu);
>  int wbinvd_on_all_cpus(void);
> -bool wakeup_cpu0(void);
> +void wakeup_cpu0_if_needed(void);
>
>  void native_smp_send_reschedule(int cpu);
>  void native_send_call_func_ipi(const struct cpumask *mask);
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index f877150a91da..9547d870ee27 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1659,7 +1659,7 @@ void play_dead_common(void)
>         local_irq_disable();
>  }
>
> -bool wakeup_cpu0(void)
> +static bool wakeup_cpu0(void)
>  {
>         if (smp_processor_id() == 0 && enable_start_cpu0)
>                 return true;
> @@ -1667,6 +1667,13 @@ bool wakeup_cpu0(void)
>         return false;
>  }
>
> +void wakeup_cpu0_if_needed(void)
> +{
> +       if (wakeup_cpu0())
> +               start_cpu0();

Note that all of the callers of wakeup_cpu0 do the above, so maybe
make them all use the new function?

In which case it can be rewritten in the following way

void cond_wakeup_cpu0(void)
{
        if (smp_processor_id() == 0 && enable_start_cpu0)
                start_cpu0();
}
EXPORT_SYMBOL_GPL(cond_wakeup_cpu0);

Also please add a proper kerneldoc comment to it and maybe drop the
comments at the call sites?


> +}
> +EXPORT_SYMBOL_GPL(wakeup_cpu0_if_needed);
> +
>  /*
>   * We need to flush the caches before going to sleep, lest we have
>   * dirty data in our caches when we come back up.
> @@ -1737,8 +1744,7 @@ static inline void mwait_play_dead(void)
>                 /*
>                  * If NMI wants to wake up CPU0, start CPU0.
>                  */
> -               if (wakeup_cpu0())
> -                       start_cpu0();
> +               wakeup_cpu0_if_needed();
>         }
>  }
>
> @@ -1752,8 +1758,7 @@ void hlt_play_dead(void)
>                 /*
>                  * If NMI wants to wake up CPU0, start CPU0.
>                  */
> -               if (wakeup_cpu0())
> -                       start_cpu0();
> +               wakeup_cpu0_if_needed();
>         }
>  }
>
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index 768a6b4d2368..de15116b754a 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -545,8 +545,7 @@ static int acpi_idle_play_dead(struct cpuidle_device *dev, int index)
>
>  #if defined(CONFIG_X86) && defined(CONFIG_HOTPLUG_CPU)
>                 /* If NMI wants to wake up CPU0, start CPU0. */
> -               if (wakeup_cpu0())
> -                       start_cpu0();
> +               wakeup_cpu0_if_needed();
>  #endif
>         }
>
> --
> 2.30.2
>