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

Michal Schmidt
2005-05-25T20:40:25Z

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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

[-- Attachment #2: cpufreq-RT.diff --]
[-- Type: text/x-patch, Size: 4205 bytes --]

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