lkml.org 
[lkml]   [2014]   [Dec]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v2] cpufreq: suspend cpufreq governors on shutdown
From
On 24 December 2014 at 11:39, Doug Anderson <dianders@chromium.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@chromium.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@linaro.org>


\
 
 \ /
  Last update: 2014-12-29 05:21    [W:0.040 / U:1.300 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site