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

[Paul E. McKenney]

On Mon, Sep 21, 2020 at 12:37:41PM +0200, Borislav Petkov wrote:
> 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>

Reviewed-by: Paul E. McKenney <paulmckrcu@xxxxxxxxxx>

> ---
>  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.
> 
> https://people.kernel.org/tglx/notes-about-netiquette