Messages in this thread | | | Date | Wed, 24 Dec 2014 07:16:00 +0530 | Subject | Re: [PATCH] cpufreq: suspend cpufreq governors on shutdown | From | Viresh Kumar <> |
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On 24 December 2014 at 05:41, 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:
Can you also add what exactly happens in such deadlock? Some lockdeps? Or just a hang ?
> 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. > > Let's avoid the race by stopping the cpufreq governor at shutdown, > which is a sensible thing to do anyway. > > Signed-off-by: Doug Anderson <dianders@chromium.org> > --- > NOTE: This was developed / tested / on a 3.14 kernel with backports. > I have confirmed that it compiles on a mainline kernel and doesn't > crash, but I haven't verified that there isn't some other fix in > mainline that also fixes this problem. If you are aware of such a fix > then please drop this patch.
No, its a new problem.
> drivers/cpufreq/cpufreq.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index a09a29c..bd89721 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 +2551,15 @@ int cpufreq_unregister_driver(struct cpufreq_driver *driver) > } > EXPORT_SYMBOL_GPL(cpufreq_unregister_driver); > > +static void cpufreq_shutdown(void) > +{ > + cpufreq_suspend(); > +} > + > +static struct syscore_ops cpufreq_syscore_ops = { > + .shutdown = cpufreq_shutdown,
directly pass cpufreq_suspend() here and add a note over the cpufreq_syscore_ops on why it exists here.
> +}; > + > static int __init cpufreq_core_init(void) > { > if (cpufreq_disabled()) > @@ -2558,6 +2568,8 @@ 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); > -- > 2.2.0.rc0.207.ga3a616c >
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