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Commit 6810b548 authored by Andi Kleen's avatar Andi Kleen Committed by Linus Torvalds
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[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: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent ac71d12c

drivers/cpufreq/cpufreq_ondemand.c

+20 −8
Original line number Diff line number Diff line
@@ -74,6 +74,8 @@ static unsigned int dbs_enable; /* number of CPUs using this policy */ 
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;
@@ -364,7 +366,7 @@ static void do_dbs_timer(void *data) 
	mutex_lock(&dbs_mutex);

	for_each_online_cpu(i)

		dbs_check_cpu(i);

	schedule_delayed_work(&dbs_work,

	queue_delayed_work(dbs_workq, &dbs_work,

			   usecs_to_jiffies(dbs_tuners_ins.sampling_rate));

	mutex_unlock(&dbs_mutex);

}
@@ -372,15 +374,21 @@ static void do_dbs_timer(void *data) 
static inline void dbs_timer_init(void)

{

	INIT_WORK(&dbs_work, do_dbs_timer, NULL);

	schedule_delayed_work(&dbs_work,

	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 int __init cpufreq_gov_dbs_init(void) 


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);

}