Any attempt to write to one of the sysfs cpufreq variables results in a
write error such as
# echo performance >/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
-bash: echo: write error: Invalid argument
that is caused by lock contention. This patch is not a solution but a
workaround to demonstrate the situation.
Signed-off-by: Carsten Emde <C.Emde@xxxxxxxxx>
---
drivers/cpufreq/cpufreq.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
Index: linux-3.18.7-rt1/drivers/cpufreq/cpufreq.c
===================================================================
--- linux-3.18.7-rt1.orig/drivers/cpufreq/cpufreq.c
+++ linux-3.18.7-rt1/drivers/cpufreq/cpufreq.c
@@ -205,8 +205,16 @@ struct cpufreq_policy *cpufreq_cpu_get(u
if (cpufreq_disabled() || (cpu >= nr_cpu_ids))
return NULL;
- if (!down_read_trylock(&cpufreq_rwsem))
- return NULL;
+ if (!down_read_trylock(&cpufreq_rwsem)) {
+ struct rt_mutex *rtm = &cpufreq_rwsem.lock;
+ struct task_struct *owner = rtm->owner;
+ if (owner->pid != current->pid) {
+ printk(KERN_INFO
+ "%s: owner->pid %d (%s), current->pid %d\n",
+ __func__, owner->pid, owner->comm, current->pid);
+ return NULL;
+ }
+ }
/* get the cpufreq driver */
read_lock_irqsave(&cpufreq_driver_lock, flags);
--
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