On 24 December 2014 at 11:39, Doug Anderson <[email protected]> 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 <[email protected]> > --- > 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 <[email protected]> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
