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

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Date:   Mon, 21 Sep 2020 15:38:21 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>,
        Borislav Petkov <bp@...en8.de>
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 3:32 PM Paul E. McKenney <paulmck@...nel.org> wrote:
>
> 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@...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>
>
> Reviewed-by: Paul E. McKenney <paulmckrcu@...nel.org>

OK

Applied as 5.9-rc7 material, thanks!

> > ---
> >  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