[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>

1 files changed, 20 insertions, 8 deletions

diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index 956d121cb161..3e6ffcaa5af4 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -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;
@@ -364,23 +366,29 @@ 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,
-                        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 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);
 }