On 08/06/2014 04:10 AM, Viresh Kumar wrote: > On 6 August 2014 03:36, Saravana Kannan <skan...@codeaurora.org> wrote: >> Stephen and I looked into this. This is not a sysfs framework difference. >> The reason we don't have this issue when we use global tunables is because >> we add the attribute group to the cpufreq_global_kobject and that kobject >> doesn't have a kobj_type ops similar to the per policy kobject. So, >> read/write to those attributes do NOT go through the generic show/store ops >> that wrap every other cpufreq framework attribute read/writes. >> >> So, none of those read/write do any kind of locking. They don't race with >> POLICY_EXIT (because we remove the sysfs group first thing in POLICY_EXIT) >> but might still race with START/STOPs (not sure, haven't looked closely >> yet). >> >> For example, writing to sampling_rate of ondemand governor might cause a >> race in update_sampling_rate(). It could race and happen between a STOP and >> POLICY_EXIT (triggered by hotplug, gov change, etc). > > This sounds good but I couldn't prove it. Doing this on my dual core exynos > doesn't give me that crash report and it should?
Are you sure you're not seeing another lockdep warning? That was my problem -- there was an xfs related lockdep warning which then resulted in lockdep being disabled from that point on. P. > > diff --git a/drivers/cpufreq/exynos-cpufreq.c > b/drivers/cpufreq/exynos-cpufreq.c > index 1e0ec57..027b6f7 100644 > --- a/drivers/cpufreq/exynos-cpufreq.c > +++ b/drivers/cpufreq/exynos-cpufreq.c > @@ -139,7 +139,7 @@ static int exynos_cpufreq_cpu_init(struct > cpufreq_policy *policy) > } > > static struct cpufreq_driver exynos_driver = { > - .flags = CPUFREQ_STICKY | CPUFREQ_NEED_INITIAL_FREQ_CHECK, > + .flags = CPUFREQ_STICKY | > CPUFREQ_NEED_INITIAL_FREQ_CHECK | CPUFREQ_HAVE_GOVERNOR_PER_POLICY, > .verify = cpufreq_generic_frequency_table_verify, > .target_index = exynos_target, > .get = cpufreq_generic_get, > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/