[Patch 2/2] cpufreq: fix a lockdep warning

From: Amerigo Wang
Date: Thu Mar 04 2010 - 03:24:42 EST

There is no need to do sysfs_remove_link() or kobject_put() etc.
when policy_rwsem_write is held, move them after releasing the lock.

This fixes the lockdep warning:

halt/4071 is trying to acquire lock:
(s_active){++++.+}, at: [<c0000000001ef868>] .sysfs_addrm_finish+0x58/0xc0

but task is already holding lock:
(&per_cpu(cpu_policy_rwsem, cpu)){+.+.+.}, at: [<c0000000004cd6ac>] .lock_policy_rwsem_write+0x84/0xf4

Reported-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: WANG Cong <amwang@xxxxxxxxxx>
Cc: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
Cc: Dave Jones <davej@xxxxxxxxxx>

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 67bc2ec..e196084 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1113,6 +1113,8 @@ static int __cpufreq_remove_dev(struct sys_device *sys_dev)
unsigned int cpu = sys_dev->id;
unsigned long flags;
struct cpufreq_policy *data;
+ struct kobject *kobj;
+ struct completion *cmp;
struct sys_device *cpu_sys_dev;
unsigned int j;
@@ -1141,10 +1143,11 @@ static int __cpufreq_remove_dev(struct sys_device *sys_dev)
dprintk("removing link\n");
cpumask_clear_cpu(cpu, data->cpus);
spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
- sysfs_remove_link(&sys_dev->kobj, "cpufreq");
+ kobj = &sys_dev->kobj;
+ sysfs_remove_link(kobj, "cpufreq");
return 0;
@@ -1181,7 +1184,10 @@ static int __cpufreq_remove_dev(struct sys_device *sys_dev)
data->governor->name, CPUFREQ_NAME_LEN);
cpu_sys_dev = get_cpu_sysdev(j);
- sysfs_remove_link(&cpu_sys_dev->kobj, "cpufreq");
+ kobj = &cpu_sys_dev->kobj;
+ unlock_policy_rwsem_write(cpu);
+ sysfs_remove_link(kobj, "cpufreq");
+ lock_policy_rwsem_write(cpu);
@@ -1192,19 +1198,22 @@ static int __cpufreq_remove_dev(struct sys_device *sys_dev)
if (cpufreq_driver->target)
__cpufreq_governor(data, CPUFREQ_GOV_STOP);

- kobject_put(&data->kobj);
+ kobj = &data->kobj;
+ cmp = &data->kobj_unregister;
+ unlock_policy_rwsem_write(cpu);
+ kobject_put(kobj);

/* we need to make sure that the underlying kobj is actually
* not referenced anymore by anybody before we proceed with
* unloading.
dprintk("waiting for dropping of refcount\n");
- wait_for_completion(&data->kobj_unregister);
+ wait_for_completion(cmp);
dprintk("wait complete\n");

+ lock_policy_rwsem_write(cpu);
if (cpufreq_driver->exit)

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