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[CPUFREQ] Fix ondemand vs suspend deadlock 

Rootcaused the bug to a deadlock in cpufreq and ondemand. Due to non-existent
ordering between cpu_hotplug lock and dbs_mutex. Basically a race condition
between cpu_down() and do_dbs_timer().

cpu_down() flow:
* cpu_down() call for CPU 1
* Takes hot plug lock
* Calls pre down notifier
*     cpufreq notifier handler calls cpufreq_driver_target() which takes
      cpu_hotplug lock again. OK as cpu_hotplug lock is recursive in same
      process context
* CPU 1 goes down
* Calls post down notifier
*     cpufreq notifier handler calls ondemand event stop which takes dbs_mutex

So, cpu_hotplug lock is taken before dbs_mutex in this flow.

do_dbs_timer is triggerred by a periodic timer event.
It first takes dbs_mutex and then takes cpu_hotplug lock in
cpufreq_driver_target().
Note the reverse order here compared to above. So, if this timer event happens
at right moment during cpu_down, system will deadlok.

Attached patch fixes the issue for both ondemand and conservative.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Dave Jones <davej@redhat.com>
This commit is contained in:
Venkatesh Pallipadi 2006-06-21 15:18:34 -07:00 committed by Dave Jones
parent 9ed059e155
commit 4ec223d02f
2 changed files with 24 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
drivers/cpufreq/cpufreq_conservative.c
View File

@ -72,6 +72,14 @@ 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
*/
static DEFINE_MUTEX (dbs_mutex);
static DECLARE_WORK (dbs_work, do_dbs_timer, NULL);
@ -414,12 +422,14 @@ static void dbs_check_cpu(int cpu)
static void do_dbs_timer(void *data)
{
int i;
lock_cpu_hotplug();
mutex_lock(&dbs_mutex);
for_each_online_cpu(i)
dbs_check_cpu(i);
schedule_delayed_work(&dbs_work,
usecs_to_jiffies(dbs_tuners_ins.sampling_rate));
mutex_unlock(&dbs_mutex);
unlock_cpu_hotplug();
}
static inline void dbs_timer_init(void)
@ -514,6 +524,7 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
break;
case CPUFREQ_GOV_LIMITS:
lock_cpu_hotplug();
mutex_lock(&dbs_mutex);
if (policy->max < this_dbs_info->cur_policy->cur)
__cpufreq_driver_target(
@ -524,6 +535,7 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
this_dbs_info->cur_policy,
policy->min, CPUFREQ_RELATION_L);
mutex_unlock(&dbs_mutex);
unlock_cpu_hotplug();
break;
}
return 0;

12
drivers/cpufreq/cpufreq_ondemand.c
View File

@ -71,6 +71,14 @@ 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
*/
static DEFINE_MUTEX (dbs_mutex);
static DECLARE_WORK (dbs_work, do_dbs_timer, NULL);
@ -363,12 +371,14 @@ static void dbs_check_cpu(int cpu)
static void do_dbs_timer(void *data)
{
int i;
lock_cpu_hotplug();
mutex_lock(&dbs_mutex);
for_each_online_cpu(i)
dbs_check_cpu(i);
queue_delayed_work(dbs_workq, &dbs_work,
usecs_to_jiffies(dbs_tuners_ins.sampling_rate));
mutex_unlock(&dbs_mutex);
unlock_cpu_hotplug();
}
static inline void dbs_timer_init(void)
@ -469,6 +479,7 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
break;
case CPUFREQ_GOV_LIMITS:
lock_cpu_hotplug();
mutex_lock(&dbs_mutex);
if (policy->max < this_dbs_info->cur_policy->cur)
__cpufreq_driver_target(
@ -479,6 +490,7 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
this_dbs_info->cur_policy,
policy->min, CPUFREQ_RELATION_L);
mutex_unlock(&dbs_mutex);
unlock_cpu_hotplug();
break;
}
return 0;