[REGRESSION] kobject handling in cpufreq

[REGRESSION] kobject handling in cpufreq

[Balaji Rao]

Hi greg,

I encountered a regression in linux-2.6.git which prevented the system from shutting down. I found that it 
was 'waiting_for_completion' on kobj_unregister.The same thing happened when I tried to take CPUs offline.

git-bisect pointed me to this commit :

commit c10997f6575f476ff38442fa18fd4a0d80345f9d
Author: Greg Kroah-Hartman <gregkh@suse.de>
Date:   Thu Dec 20 08:13:05 2007 -0800

    Kobject: convert drivers/* from kobject_unregister() to kobject_put()

In the file drivers/cpufreq/cpufreq.c, you have not replaced one occurrence of kobject_unregister with kobject_put. 
Apparently its because of the kobject_put in the subsequent line.

@@ -1030,8 +1030,6 @@ static int __cpufreq_remove_dev (struct sys_device * sys_dev)
 
        unlock_policy_rwsem_write(cpu);
 
-       kobject_unregister(&data->kobj);
-
        kobject_put(&data->kobj);
 
        /* we need to make sure that the underlying kobj is actually

Now, this can be fixed by adding another kobject_put. But having two kobject_puts in consequent lines tells us that there 
should be two references to the kobject at that point. So, I believe that it is safe to remove the kobject_get 
corresponding to the existing kobject_put to fix this.

Signed-off-by: Balaji Rao <balajirrao@gmail.com>

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 64926aa..2158786 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1004,17 +1004,6 @@ static int __cpufreq_remove_dev (struct sys_device * sys_dev)
 		unlock_policy_rwsem_write(cpu);
 		return 0;
 	}
-#endif
-
-
-	if (!kobject_get(&data->kobj)) {
-		spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
-		cpufreq_debug_enable_ratelimit();
-		unlock_policy_rwsem_write(cpu);
-		return -EFAULT;
-	}
-
-#ifdef CONFIG_SMP
 
 #ifdef CONFIG_HOTPLUG_CPU
 	cpufreq_cpu_governor[cpu] = data->governor;
-- 
regards,
balaji rao

Re: [REGRESSION] kobject handling in cpufreq

[Greg KH]

On Sat, Feb 09, 2008 at 12:52:40AM +0530, Balaji Rao wrote:
> Hi greg,
> 
> I encountered a regression in linux-2.6.git which prevented the system from shutting down. I found that it 
> was 'waiting_for_completion' on kobj_unregister.The same thing happened when I tried to take CPUs offline.
> 
> git-bisect pointed me to this commit :
> 
> commit c10997f6575f476ff38442fa18fd4a0d80345f9d
> Author: Greg Kroah-Hartman <gregkh@suse.de>
> Date:   Thu Dec 20 08:13:05 2007 -0800
> 
>     Kobject: convert drivers/* from kobject_unregister() to kobject_put()
> 
> In the file drivers/cpufreq/cpufreq.c, you have not replaced one occurrence of kobject_unregister with kobject_put. 
> Apparently its because of the kobject_put in the subsequent line.
> 
> @@ -1030,8 +1030,6 @@ static int __cpufreq_remove_dev (struct sys_device * sys_dev)
>  
>         unlock_policy_rwsem_write(cpu);
>  
> -       kobject_unregister(&data->kobj);
> -
>         kobject_put(&data->kobj);
>  
>         /* we need to make sure that the underlying kobj is actually
> 
> Now, this can be fixed by adding another kobject_put. But having two kobject_puts in consequent lines tells us that there 
> should be two references to the kobject at that point. So, I believe that it is safe to remove the kobject_get 
> corresponding to the existing kobject_put to fix this.
> 
> Signed-off-by: Balaji Rao <balajirrao@gmail.com>

This looks correct to me, nice catch.

Acked-by: Greg Kroah-Hartman <gregkh@suse.de>

thanks,

greg k-h