Commit b14893a62c73af0eca414cfed505b8c09efc613c although it was very much needed to properly cleanup ondemand timer, opened-up 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 http://lkml.indiana.edu/hypermail/linux/kernel/0907.0/00820.html and few others.. Signed-off-by: Venkatesh Pallipadi <[email protected]> --- drivers/cpufreq/cpufreq.c | 4 ++-- drivers/cpufreq/cpufreq_conservative.c | 27 +++++++++++---------------- drivers/cpufreq/cpufreq_ondemand.c | 27 +++++++++++---------------- 3 files changed, 24 insertions(+), 34 deletions(-) diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 6e2ec0b..c7fe16e 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -1070,8 +1070,6 @@ static int __cpufreq_remove_dev(struct sys_device *sys_dev) spin_unlock_irqrestore(&cpufreq_driver_lock, flags); #endif - unlock_policy_rwsem_write(cpu); - if (cpufreq_driver->target) __cpufreq_governor(data, CPUFREQ_GOV_STOP); @@ -1088,6 +1086,8 @@ static int __cpufreq_remove_dev(struct sys_device *sys_dev) if (cpufreq_driver->exit) cpufreq_driver->exit(data); + unlock_policy_rwsem_write(cpu); + free_cpumask_var(data->related_cpus); free_cpumask_var(data->cpus); kfree(data); diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c index 7fc58af..58889f2 100644 --- a/drivers/cpufreq/cpufreq_conservative.c +++ b/drivers/cpufreq/cpufreq_conservative.c @@ -70,15 +70,10 @@ 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 protects dbs_enable in governor start/stop. It also + * serializes governor limit_change with do_dbs_timer. We do not want + * do_dbs_timer to run when user is changing the governor or limits. */ static DEFINE_MUTEX(dbs_mutex); @@ -488,18 +483,17 @@ static void do_dbs_timer(struct work_struct *work) delay -= jiffies % delay; - if (lock_policy_rwsem_write(cpu) < 0) - return; + mutex_lock(&dbs_mutex); if (!dbs_info->enable) { - unlock_policy_rwsem_write(cpu); + mutex_unlock(&dbs_mutex); return; } dbs_check_cpu(dbs_info); queue_delayed_work_on(cpu, kconservative_wq, &dbs_info->work, delay); - unlock_policy_rwsem_write(cpu); + mutex_unlock(&dbs_mutex); } static inline void dbs_timer_init(struct cpu_dbs_info_s *dbs_info) @@ -590,15 +584,16 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy, &dbs_cpufreq_notifier_block, CPUFREQ_TRANSITION_NOTIFIER); } - dbs_timer_init(this_dbs_info); - mutex_unlock(&dbs_mutex); + dbs_timer_init(this_dbs_info); + 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--; diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c index 1911d17..246ae14 100644 --- a/drivers/cpufreq/cpufreq_ondemand.c +++ b/drivers/cpufreq/cpufreq_ondemand.c @@ -78,15 +78,10 @@ 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 protects dbs_enable in governor start/stop. It also + * serializes governor limit_change with do_dbs_timer. We do not want + * do_dbs_timer to run when user is changing the governor or limits. */ static DEFINE_MUTEX(dbs_mutex); @@ -494,11 +489,10 @@ static void do_dbs_timer(struct work_struct *work) delay -= jiffies % delay; - if (lock_policy_rwsem_write(cpu) < 0) - return; + mutex_lock(&dbs_mutex); if (!dbs_info->enable) { - unlock_policy_rwsem_write(cpu); + mutex_unlock(&dbs_mutex); return; } @@ -517,7 +511,7 @@ static void do_dbs_timer(struct work_struct *work) dbs_info->freq_lo, CPUFREQ_RELATION_H); } queue_delayed_work_on(cpu, kondemand_wq, &dbs_info->work, delay); - unlock_policy_rwsem_write(cpu); + mutex_unlock(&dbs_mutex); } static inline void dbs_timer_init(struct cpu_dbs_info_s *dbs_info) @@ -598,14 +592,15 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy, max(min_sampling_rate, latency * LATENCY_MULTIPLIER); } - dbs_timer_init(this_dbs_info); - mutex_unlock(&dbs_mutex); + + dbs_timer_init(this_dbs_info); 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); -- 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
