[CPUFREQ] fix a lockdep warning
Amerigo Wang [Thu, 4 Mar 2010 08:23:46 +0000 (03:23 -0500)]
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@kernel.crashing.org>
Signed-off-by: WANG Cong <amwang@redhat.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Dave Jones <davej@redhat.com>

drivers/cpufreq/cpufreq.c

index 2d5d575..75d293e 100644 (file)
@@ -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;
 #ifdef CONFIG_SMP
        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;
                cpufreq_cpu_put(data);
                cpufreq_debug_enable_ratelimit();
                unlock_policy_rwsem_write(cpu);
+               sysfs_remove_link(kobj, "cpufreq");
                return 0;
        }
 #endif
@@ -1181,7 +1184,10 @@ static int __cpufreq_remove_dev(struct sys_device *sys_dev)
                                data->governor->name, CPUFREQ_NAME_LEN);
 #endif
                        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);
                        cpufreq_cpu_put(data);
                }
        }
@@ -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)
                cpufreq_driver->exit(data);
-
        unlock_policy_rwsem_write(cpu);
 
        free_cpumask_var(data->related_cpus);