[PATCH] x86_64: Move ondemand timer into own work queue
Taking the cpu hotplug semaphore in a normal events workqueue
is unsafe because other tasks can wait for any workqueues with
it hold. This results in a deadlock.
Move the DBS timer into its own work queue which is not
affected by other work queue flushes to avoid this.
Has been acked by Venkatesh.
Cc: venkatesh.pallipadi@intel.com
Cc: cpufreq@lists.linux.org.uk
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index 956d121..3e6ffca 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -74,6 +74,8 @@
static DEFINE_MUTEX (dbs_mutex);
static DECLARE_WORK (dbs_work, do_dbs_timer, NULL);
+static struct workqueue_struct *dbs_workq;
+
struct dbs_tuners {
unsigned int sampling_rate;
unsigned int sampling_down_factor;
@@ -364,23 +366,29 @@
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));
+ queue_delayed_work(dbs_workq, &dbs_work,
+ usecs_to_jiffies(dbs_tuners_ins.sampling_rate));
mutex_unlock(&dbs_mutex);
}
static inline void dbs_timer_init(void)
{
INIT_WORK(&dbs_work, do_dbs_timer, NULL);
- schedule_delayed_work(&dbs_work,
- usecs_to_jiffies(dbs_tuners_ins.sampling_rate));
+ if (!dbs_workq)
+ dbs_workq = create_singlethread_workqueue("ondemand");
+ if (!dbs_workq) {
+ printk(KERN_ERR "ondemand: Cannot initialize kernel thread\n");
+ return;
+ }
+ queue_delayed_work(dbs_workq, &dbs_work,
+ usecs_to_jiffies(dbs_tuners_ins.sampling_rate));
return;
}
static inline void dbs_timer_exit(void)
{
- cancel_delayed_work(&dbs_work);
- return;
+ if (dbs_workq)
+ cancel_rearming_delayed_workqueue(dbs_workq, &dbs_work);
}
static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
@@ -489,8 +497,12 @@
static void __exit cpufreq_gov_dbs_exit(void)
{
- /* Make sure that the scheduled work is indeed not running */
- flush_scheduled_work();
+ /* Make sure that the scheduled work is indeed not running.
+ Assumes the timer has been cancelled first. */
+ if (dbs_workq) {
+ flush_workqueue(dbs_workq);
+ destroy_workqueue(dbs_workq);
+ }
cpufreq_unregister_governor(&cpufreq_gov_dbs);
}