Re: [patch] Real-Time Preemption, -RT-2.6.12-rc4-V0.7.47-06

[Michal Schmidt]

Hi Ingo,

I'm now running -RT-2.6.12-rc4-V0.7.47-08 on amd64.
I use cpufreq, but with the RT kernel it triggers "Kernel BUG at 
"kernel/latency.c":1295" (the check for preempt_count underflow).

I'm attaching a patch which changes a semaphore in cpufreq into a 
completion. With this patch, my system runs OK even with cpufreqd.

Michal
diff -Nurp -X linux-2.6.12-rc4-RT-mich/Documentation/dontdiff linux-2.6.12-rc4-RT/drivers/cpufreq/cpufreq.c linux-2.6.12-rc4-RT-mich/drivers/cpufreq/cpufreq.c
--- linux-2.6.12-rc4-RT/drivers/cpufreq/cpufreq.c	2005-05-25 22:23:24.000000000 +0200
+++ linux-2.6.12-rc4-RT-mich/drivers/cpufreq/cpufreq.c	2005-05-25 21:56:43.000000000 +0200
@@ -605,7 +605,7 @@ static int cpufreq_add_dev (struct sys_d
 	policy->cpu = cpu;
 	policy->cpus = cpumask_of_cpu(cpu);
 
-	init_MUTEX_LOCKED(&policy->lock);
+	init_completion(&policy->done);
 	init_completion(&policy->kobj_unregister);
 	INIT_WORK(&policy->update, handle_update, (void *)(long)cpu);
 
@@ -646,7 +646,7 @@ static int cpufreq_add_dev (struct sys_d
 	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
 	policy->governor = NULL; /* to assure that the starting sequence is
 				  * run in cpufreq_set_policy */
-	up(&policy->lock);
+	complete(&policy->done);
 	
 	/* set default policy */
 	
@@ -765,11 +765,11 @@ static int cpufreq_remove_dev (struct sy
 	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
 #endif
 
-	down(&data->lock);
+	wait_for_completion(&data->done);
 	if (cpufreq_driver->target)
 		__cpufreq_governor(data, CPUFREQ_GOV_STOP);
 	cpufreq_driver->target = NULL;
-	up(&data->lock);
+	complete(&data->done);
 
 	kobject_unregister(&data->kobj);
 
@@ -842,7 +842,7 @@ unsigned int cpufreq_get(unsigned int cp
 	if (!cpufreq_driver->get)
 		goto out;
 
-	down(&policy->lock);
+	wait_for_completion(&policy->done);
 
 	ret = cpufreq_driver->get(cpu);
 
@@ -855,7 +855,7 @@ unsigned int cpufreq_get(unsigned int cp
 		}
 	}
 
-	up(&policy->lock);
+	complete(&policy->done);
 
  out:
 	cpufreq_cpu_put(policy);
@@ -1136,11 +1136,11 @@ int cpufreq_driver_target(struct cpufreq
 	if (!policy)
 		return -EINVAL;
 
-	down(&policy->lock);
+	wait_for_completion(&policy->done);
 
 	ret = __cpufreq_driver_target(policy, target_freq, relation);
 
-	up(&policy->lock);
+	complete(&policy->done);
 
 	cpufreq_cpu_put(policy);
 
@@ -1177,9 +1177,9 @@ int cpufreq_governor(unsigned int cpu, u
 	if (!policy)
 		return -EINVAL;
 
-	down(&policy->lock);
+	wait_for_completion(&policy->done);
 	ret = __cpufreq_governor(policy, event);
-	up(&policy->lock);
+	complete(&policy->done);
 
 	cpufreq_cpu_put(policy);
 
@@ -1246,9 +1246,9 @@ int cpufreq_get_policy(struct cpufreq_po
 	if (!cpu_policy)
 		return -EINVAL;
 
-	down(&cpu_policy->lock);
+	wait_for_completion(&cpu_policy->done);
 	memcpy(policy, cpu_policy, sizeof(struct cpufreq_policy));
-	up(&cpu_policy->lock);
+	complete(&cpu_policy->done);
 
 	cpufreq_cpu_put(cpu_policy);
 
@@ -1360,7 +1360,7 @@ int cpufreq_set_policy(struct cpufreq_po
 		return -EINVAL;
 
 	/* lock this CPU */
-	down(&data->lock);
+	wait_for_completion(&data->done);
 
 	ret = __cpufreq_set_policy(data, policy);
 	data->user_policy.min = data->min;
@@ -1368,7 +1368,7 @@ int cpufreq_set_policy(struct cpufreq_po
 	data->user_policy.policy = data->policy;
 	data->user_policy.governor = data->governor;
 
-	up(&data->lock);
+	complete(&data->done);
 	cpufreq_cpu_put(data);
 
 	return ret;
@@ -1392,7 +1392,7 @@ int cpufreq_update_policy(unsigned int c
 	if (!data)
 		return -ENODEV;
 
-	down(&data->lock);
+	wait_for_completion(&data->done);
 
 	dprintk("updating policy for CPU %u\n", cpu);
 	memcpy(&policy, 
@@ -1405,7 +1405,7 @@ int cpufreq_update_policy(unsigned int c
 
 	ret = __cpufreq_set_policy(data, &policy);
 
-	up(&data->lock);
+	complete(&data->done);
 
 	cpufreq_cpu_put(data);
 	return ret;
diff -Nurp -X linux-2.6.12-rc4-RT-mich/Documentation/dontdiff linux-2.6.12-rc4-RT/include/linux/cpufreq.h linux-2.6.12-rc4-RT-mich/include/linux/cpufreq.h
--- linux-2.6.12-rc4-RT/include/linux/cpufreq.h	2005-05-25 22:23:26.000000000 +0200
+++ linux-2.6.12-rc4-RT-mich/include/linux/cpufreq.h	2005-05-25 21:49:25.000000000 +0200
@@ -81,7 +81,7 @@ struct cpufreq_policy {
         unsigned int		policy; /* see above */
 	struct cpufreq_governor	*governor; /* see below */
 
- 	struct semaphore	lock;   /* CPU ->setpolicy or ->target may
+ 	struct completion	done;   /* CPU ->setpolicy or ->target may
 					   only be called once a time */
 
 	struct work_struct	update; /* if update_policy() needs to be