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

[Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>]

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@xxxxxxxxx>
Fixes: 8cdddd182bd7 ("CPI: processor: Fix CPU0 wakeup in acpi_idle_play_dead()")
Cc: <stable@xxxxxxxxxxxxxxx> # 5.10+
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
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.
+ */
+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