linux-kernel - Re: [PATCH] rcu/tree: Export rcu_idle

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Date:   Mon, 21 Sep 2020 14:15:58 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Borislav Petkov <bp@...en8.de>,
        "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Sven Joachim <svenjoac@....de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Tony Luck <tony.luck@...el.com>, Len Brown <lenb@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org
Subject: Re: [PATCH] rcu/tree: Export rcu_idle_{enter,exit} to module

On Mon, Sep 21, 2020 at 12:37 PM Borislav Petkov <bp@...en8.de> 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@...radead.org>
> >
> > 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@...e.de>
> 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@....de>
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Borislav Petkov <bp@...e.de>

Well, I guess I should take this through cpuidle?

Any concerns about doing that?  Paul?

> ---
>  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