linux-kernel - Re: [PATCH v2] cpufreq: suspend cpufreq governors on shutdown

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Date:	Fri, 30 Jan 2015 01:14:12 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Doug Anderson <dianders@...omium.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Chris Zhong <zyw@...k-chips.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Sonny Rao <sonnyrao@...omium.org>,
	Dylan Reid <dgreid@...omium.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] cpufreq: suspend cpufreq governors on shutdown

On Monday, December 29, 2014 09:45:42 AM Viresh Kumar wrote:
> On 24 December 2014 at 11:39, Doug Anderson <dianders@...omium.org> wrote:
> > We should stop cpufreq governors when we shut down the system.  If we
> > don't do this, we can end up with this deadlock:
> >
> > 1. cpufreq governor may be running on a CPU other than CPU0.
> > 2. In machine_restart() we call smp_send_stop() which stops CPUs.
> >    If one of these CPUs was actively running a cpufreq governor
> >    then it may have the mutex / spinlock needed to access the main
> >    PMIC in the system (perhaps over I2C)
> > 3. If a machine needs access to the main PMIC in order to shutdown
> >    then it will never get it since the mutex was lost when the other
> >    CPU stopped.
> > 4. We'll hang (possibly eventually hitting the hard lockup detector).
> >
> > Let's avoid the problem by stopping the cpufreq governor at shutdown,
> > which is a sensible thing to do anyway.
> >
> > Signed-off-by: Doug Anderson <dianders@...omium.org>
> > ---
> > Changes in v2:
> > - Add a comment about why we register
> > - Don't create cpufreq_shutdown() wrapper function
> >
> >  drivers/cpufreq/cpufreq.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index a09a29c..33f3d65 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -27,6 +27,7 @@
> >  #include <linux/mutex.h>
> >  #include <linux/slab.h>
> >  #include <linux/suspend.h>
> > +#include <linux/syscore_ops.h>
> >  #include <linux/tick.h>
> >  #include <trace/events/power.h>
> >
> > @@ -2550,6 +2551,14 @@ int cpufreq_unregister_driver(struct cpufreq_driver *driver)
> >  }
> >  EXPORT_SYMBOL_GPL(cpufreq_unregister_driver);
> >
> > +/*
> > + * Stop cpufreq at shutdown to make sure it isn't holding any locks
> > + * or mutexes when secondary CPUs are halted.
> > + */
> > +static struct syscore_ops cpufreq_syscore_ops = {
> > +       .shutdown = cpufreq_suspend,
> > +};
> > +
> >  static int __init cpufreq_core_init(void)
> >  {
> >         if (cpufreq_disabled())
> > @@ -2558,6 +2567,8 @@ static int __init cpufreq_core_init(void)
> >         cpufreq_global_kobject = kobject_create();
> >         BUG_ON(!cpufreq_global_kobject);
> >
> > +       register_syscore_ops(&cpufreq_syscore_ops);
> > +
> >         return 0;
> >  }
> >  core_initcall(cpufreq_core_init);
> 
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

Queued up for 3.20, thanks!


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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