"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