Messages in this thread Patch in this message | | | Date | Wed, 6 Aug 2014 13:40:30 +0530 | Subject | Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem to be held for duration of changing governors [v2] | From | Viresh Kumar <> |
| |
On 6 August 2014 03:36, Saravana Kannan <skannan@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?
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,
| |