[PATCH] rcu/tree: Export rcu_idle_{enter,exit} to module

[Borislav Petkov]

Lemme add whatever get_maintainer spits, to Cc.

On Mon, Sep 21, 2020 at 11:12:33AM +0200, Sven Joachim wrote:
> On 2020-09-15 12:32 +0200, Peter Zijlstra wrote:
> 
> > The C3 BusMaster idle code takes lock in a number of places, some deep
> > inside the ACPI code. Instead of wrapping it all in RCU_NONIDLE, have
> > the driver take over RCU-idle duty and avoid flipping RCU state back
> > and forth a lot.
> >
> > ( by marking 'C3 && bm_check' as RCU_IDLE, we _must_ call enter_bm() for
> >   that combination, otherwise we'll loose RCU-idle, this requires
> >   shuffling some code around )
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> 
> I got modpost errors in 5.9-rc6 after this patch:
> 
> ERROR: modpost: "rcu_idle_enter" [drivers/acpi/processor.ko] undefined!
> ERROR: modpost: "rcu_idle_exit" [drivers/acpi/processor.ko] undefined!
> 
> Reverting commit 1fecfdbb7acc made them go away.  Notably my
> configuration had CONFIG_ACPI_PROCESSOR=m,  changing that
> to CONFIG_ACPI_PROCESSOR=y let the build succeed as well.

I guess this. Running randconfigs on it for a while, to see what else
breaks.

---
From: Borislav Petkov <bp@xxxxxxx>
Date: Mon, 21 Sep 2020 12:31:36 +0200

Fix this link error:

  ERROR: modpost: "rcu_idle_enter" [drivers/acpi/processor.ko] undefined!
  ERROR: modpost: "rcu_idle_exit" [drivers/acpi/processor.ko] undefined!

when CONFIG_ACPI_PROCESSOR is built as module. PeterZ says that in light
of ARM needing those soon too, they should simply be exported.

Fixes: 1fecfdbb7acc ("ACPI: processor: Take over RCU-idle for C3-BM idle")
Reported-by: Sven Joachim <svenjoac@xxxxxx>
Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
---
 kernel/rcu/tree.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8ce77d9ac716..f78ee759af9c 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -673,6 +673,7 @@ void rcu_idle_enter(void)
 	lockdep_assert_irqs_disabled();
 	rcu_eqs_enter(false);
 }
+EXPORT_SYMBOL_GPL(rcu_idle_enter);
 
 #ifdef CONFIG_NO_HZ_FULL
 /**
@@ -886,6 +887,7 @@ void rcu_idle_exit(void)
 	rcu_eqs_exit(false);
 	local_irq_restore(flags);
 }
+EXPORT_SYMBOL_GPL(rcu_idle_exit);
 
 #ifdef CONFIG_NO_HZ_FULL
 /**
-- 
2.21.0

-- 
Regards/Gruss,
    Boris.

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