Re: [PATCH] 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 2:50 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>
>> ---
>>  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);
>

Sure, separate wakeup_cpu0() is no longer needed.

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

Also a good idea. v2 is coming, thanks!

>
>
>> +}
>> +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
>>
>

-- 
Vitaly