Re: [PATCH v2] ACPI: processor: Fix build when CONFIG_ACPI_PROCESSOR=m

[Vitaly Kuznetsov <vkuznets@redhat.com>]

"Rafael J. Wysocki" <rafael@kernel.org> writes:

> On Tue, Apr 6, 2021 at 4:01 PM Vitaly Kuznetsov <vkuznets@redhat.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@intel.com>
>> Fixes: 8cdddd182bd7 ("CPI: processor: Fix CPU0 wakeup in acpi_idle_play_dead()")
>> Cc: <stable@vger.kernel.org> # 5.10+
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>> Changes since v1:
>> - Rename wakeup_cpu0() to cond_wakeup_cpu0() and fold wakeup_cpu0() in
>>  as it has no other users [Rafael J. Wysocki]
>> ---
>>  arch/x86/include/asm/smp.h    |  2 +-
>>  arch/x86/kernel/smpboot.c     | 24 ++++++++++--------------
>>  drivers/acpi/processor_idle.c |  4 +---
>>  3 files changed, 12 insertions(+), 18 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
>> index 57ef2094af93..630ff08532be 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 cond_wakeup_cpu0(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..147f1bba9736 100644
>> --- a/arch/x86/kernel/smpboot.c
>> +++ b/arch/x86/kernel/smpboot.c
>> @@ -1659,13 +1659,15 @@ void play_dead_common(void)
>>         local_irq_disable();
>>  }
>>
>> -bool wakeup_cpu0(void)
>> +/*
>> + * If NMI wants to wake up CPU0, start CPU0.
>> + */
>
> Hasn't checkpatch.pl complained about this?
>

No, it didn't.

> A proper kerneldoc would be something like:
>
> /**
>  * cond_wakeup_cpu0 - Wake up CPU0 if needed.
>  *
>  * If NMI wants to wake up CPU0, start CPU0.
>  */

Yea, I didn't do that partly because of my laziness but partly because
I don't see much usage of this format in arch/x86/kernel/[smpboot.c]. I
can certainly do v3 if it's prefered.

>
>> +void cond_wakeup_cpu0(void)
>>  {
>>         if (smp_processor_id() == 0 && enable_start_cpu0)
>> -               return true;
>> -
>> -       return false;
>> +               start_cpu0();
>>  }
>> +EXPORT_SYMBOL_GPL(cond_wakeup_cpu0);
>>
>>  /*
>>   * We need to flush the caches before going to sleep, lest we have
>> @@ -1734,11 +1736,8 @@ static inline void mwait_play_dead(void)
>>                 __monitor(mwait_ptr, 0, 0);
>>                 mb();
>>                 __mwait(eax, 0);
>> -               /*
>> -                * If NMI wants to wake up CPU0, start CPU0.
>> -                */
>> -               if (wakeup_cpu0())
>> -                       start_cpu0();
>> +
>> +               cond_wakeup_cpu0();
>>         }
>>  }
>>
>> @@ -1749,11 +1748,8 @@ void hlt_play_dead(void)
>>
>>         while (1) {
>>                 native_halt();
>> -               /*
>> -                * If NMI wants to wake up CPU0, start CPU0.
>> -                */
>> -               if (wakeup_cpu0())
>> -                       start_cpu0();
>> +
>> +               cond_wakeup_cpu0();
>>         }
>>  }
>>
>> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
>> index 768a6b4d2368..4e2d76b8b697 100644
>> --- a/drivers/acpi/processor_idle.c
>> +++ b/drivers/acpi/processor_idle.c
>> @@ -544,9 +544,7 @@ static int acpi_idle_play_dead(struct cpuidle_device *dev, int index)
>>                         return -ENODEV;
>>
>>  #if defined(CONFIG_X86) && defined(CONFIG_HOTPLUG_CPU)
>> -               /* If NMI wants to wake up CPU0, start CPU0. */
>> -               if (wakeup_cpu0())
>> -                       start_cpu0();
>> +               cond_wakeup_cpu0();
>>  #endif
>>         }
>>
>> --
>> 2.30.2
>>
>

-- 
Vitaly