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

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Date:	Mon, 29 Dec 2014 09:45:42 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Doug Anderson <dianders@...omium.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	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 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>
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