linux-kernel - Re: WARNING: suspicious RCU usage - sdhci-pltfm: SDHCI platform and OF driver helper

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Date:   Wed, 2 Sep 2020 09:03:37 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Saravana Kannan <saravanak@...gle.com>,
        open list <linux-kernel@...r.kernel.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        lkft-triage@...ts.linaro.org, rcu@...r.kernel.org,
        Linux PM <linux-pm@...r.kernel.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        John Stultz <john.stultz@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        madhuparnabhowmik10@...il.com,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: WARNING: suspicious RCU usage - sdhci-pltfm: SDHCI platform and
 OF driver helper

On Tue, 1 Sep 2020 at 19:42, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, Sep 01, 2020 at 09:13:40AM -0700, Paul E. McKenney wrote:
> > On Tue, Sep 01, 2020 at 05:50:14PM +0200, peterz@...radead.org wrote:
> > > On Tue, Sep 01, 2020 at 09:44:17AM -0600, Lina Iyer wrote:
> > > > > > > > > I could add RCU_NONIDLE for the calls to pm_runtime_put_sync_suspend()
> > > > > > > > > and pm_runtime_get_sync() in psci_enter_domain_idle_state(). Perhaps
> > > > > > > > > that's the easiest approach, at least to start with.
> > >
> > > > I think this would be nice. This should also cover the case, where PM domain
> > > > power off notification callbacks call trace function internally. Right?
> > >
> > > That's just more crap for me to clean up later :-(
> > >
> > > trace_*_rcuidle() and RCU_NONIDLE() need to die, not proliferate.
> >
> > Moving the idle-entry boundary further in is good in any number of ways.
> > But experience indicates that no matter how far you move it, there will
> > be something complex further in.  Unless you are pushing it all the way
> > into all the arch-specific code down as far as it can possibly go?
>
> Not all; the simple cpuidle drivers should be good already. The more
> complicated ones need some help.
>
> The patch provided earlier:
>
>   https://lkml.kernel.org/r/20200901104206.GU1362448@hirez.programming.kicks-ass.net
>
> should allow the complicated drivers to take over and DTRT.

Don't get me wrong, I fully support your approach by moving the
rcu_idle_enter() down as far as possible, but it seems to require more
work than just adding a simple flag for the idle states.

Lots of cpuidle drivers are using CPU_PM notifiers (grep for
cpu_pm_enter and you will see) from their idlestates ->enter()
callbacks. And for those we are already calling
rcu_irq_enter_irqson|off() in cpu_pm_notify() when firing them.

Kind regards
Uffe