Commit b14893a62c73af0eca414cfed505b8c09efc613c although it was very much needed to cleanup ondemand timer cleanly, openup a can of worms related to locking dependencies in cpufreq.
Patch here defines the need for dbs_mutex and cleans up its usage in ondemand governor. This also resolves the lockdep warnings reported here http://lkml.indiana.edu/hypermail/linux/kernel/0906.1/01925.html Signed-off-by: Venkatesh Pallipadi <[email protected]> --- drivers/cpufreq/cpufreq_ondemand.c | 37 +++++++++++++++-------------------- 1 files changed, 16 insertions(+), 21 deletions(-) diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c index 1911d17..b2d2106 100644 --- a/drivers/cpufreq/cpufreq_ondemand.c +++ b/drivers/cpufreq/cpufreq_ondemand.c @@ -78,15 +78,14 @@ static DEFINE_PER_CPU(struct cpu_dbs_info_s, cpu_dbs_info); static unsigned int dbs_enable; /* number of CPUs using this policy */ /* - * DEADLOCK ALERT! There is a ordering requirement between cpu_hotplug - * lock and dbs_mutex. cpu_hotplug lock should always be held before - * dbs_mutex. If any function that can potentially take cpu_hotplug lock - * (like __cpufreq_driver_target()) is being called with dbs_mutex taken, then - * cpu_hotplug lock should be taken before that. Note that cpu_hotplug lock - * is recursive for the same process. -Venki - * DEADLOCK ALERT! (2) : do_dbs_timer() must not take the dbs_mutex, because it - * would deadlock with cancel_delayed_work_sync(), which is needed for proper - * raceless workqueue teardown. + * dbs_mutex protects data in dbs_tuners_ins from concurrent changes on + * different CPUs. It also serializes dbs_enable usage in CPUFREQ_GOV_START + * and CPUFREQ_GOV_STOP. + * + * dbs_mutex should be always held after lock_policy_rwsem whenever needed. + * do_dbs_timer() must not take the dbs_mutex, because it would deadlock + * with cancel_delayed_work_sync(), which is needed for proper raceless + * workqueue teardown. */ static DEFINE_MUTEX(dbs_mutex); @@ -240,12 +239,10 @@ static ssize_t store_sampling_rate(struct cpufreq_policy *unused, unsigned int input; int ret; ret = sscanf(buf, "%u", &input); + if (ret != 1) + return -EINVAL; mutex_lock(&dbs_mutex); - if (ret != 1) { - mutex_unlock(&dbs_mutex); - return -EINVAL; - } dbs_tuners_ins.sampling_rate = max(input, min_sampling_rate); mutex_unlock(&dbs_mutex); @@ -258,14 +255,12 @@ static ssize_t store_up_threshold(struct cpufreq_policy *unused, unsigned int input; int ret; ret = sscanf(buf, "%u", &input); - - mutex_lock(&dbs_mutex); if (ret != 1 || input > MAX_FREQUENCY_UP_THRESHOLD || input < MIN_FREQUENCY_UP_THRESHOLD) { - mutex_unlock(&dbs_mutex); return -EINVAL; } + mutex_lock(&dbs_mutex); dbs_tuners_ins.up_threshold = input; mutex_unlock(&dbs_mutex); @@ -324,8 +319,8 @@ static ssize_t store_powersave_bias(struct cpufreq_policy *unused, mutex_lock(&dbs_mutex); dbs_tuners_ins.powersave_bias = input; - ondemand_powersave_bias_init(); mutex_unlock(&dbs_mutex); + ondemand_powersave_bias_init(); return count; } @@ -598,14 +593,16 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy, max(min_sampling_rate, latency * LATENCY_MULTIPLIER); } + mutex_unlock(&dbs_mutex); + dbs_timer_init(this_dbs_info); - mutex_unlock(&dbs_mutex); break; case CPUFREQ_GOV_STOP: - mutex_lock(&dbs_mutex); dbs_timer_exit(this_dbs_info); + + mutex_lock(&dbs_mutex); sysfs_remove_group(&policy->kobj, &dbs_attr_group); dbs_enable--; mutex_unlock(&dbs_mutex); @@ -613,14 +610,12 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy, break; case CPUFREQ_GOV_LIMITS: - mutex_lock(&dbs_mutex); if (policy->max < this_dbs_info->cur_policy->cur) __cpufreq_driver_target(this_dbs_info->cur_policy, policy->max, CPUFREQ_RELATION_H); else if (policy->min > this_dbs_info->cur_policy->cur) __cpufreq_driver_target(this_dbs_info->cur_policy, policy->min, CPUFREQ_RELATION_L); - mutex_unlock(&dbs_mutex); break; } return 0; -- 1.6.0.6 -- -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
