* venkatesh.pallipadi@xxxxxxxxx (venkatesh.pallipadi@xxxxxxxxx) wrote: > 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 <venkatesh.pallipadi@xxxxxxxxx> > --- > 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); Hrm, so.. how do we protect against concurrent : CPUFREQ_GOV_START/CPUFREQ_GOV_STOP now ? Mathieu > + > + 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 > > -- > -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
