linux-kernel - Re: [PATCH 2.6.25-rc1] cpufreq: fix cpufreq policy refcount imbalance

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Message-ID: <20080215210137.GE7583@suse.de>
Date:	Fri, 15 Feb 2008 13:01:37 -0800
From:	Greg KH <gregkh@...e.de>
To:	Yi Yang <yi.y.yang@...el.com>
Cc:	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	davej@...emonkey.org.uk, mingo@...e.hu, cpufreq@...ts.linux.org.uk,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH 2.6.25-rc1] cpufreq: fix cpufreq policy refcount
	imbalance

On Fri, Feb 15, 2008 at 07:48:41AM +0800, Yi Yang wrote:
> When one cpu is set to offline, the caller process will hang, according to
> the trace data, the problem lies in the refcount error in cpufreq driver,
> cpufreq_cpu_callback will wait for completion policy->kobj_unregister
> which is nerver completed because a refcount error in function
> __cpufreq_remove_dev in file driver/cpufreq/cpufreq.c results in not
> calling kobject release method.
> 
> In driver/cpufreq/cpufreq.c, the refcount of data->kobj isn't 1 when it
> will be unregistered, this problem didn't exist in 2.6.24 and earlier.
> 
> The root cause is kobject API switch, kobject_init_and_add and kobject_put
> replace older kobject_register and kobject_unregister in 2.6.25-rc1,
> compared to 2.6.24, kobject_unregister is deleted in function
> __cpufreq_remove_dev but it isn't replaced with kobject_put.
> 
> This patch adds kobject_put to balance refcount. I noticed Greg suggests
> it will fix a power-off issue to remove kobject_get statement block, but i
> think that isn't the best way because those code block has existed very long
> and it is helpful because the successive statements are invoking relevant
> data.
> 
> 
> Signed-off-by: Yi Yang <yi.y.yang@...el.com>

No, the additional kobject_get() needs to be removed.  I posted a patch
for this last night, and so did someone else earlier at:
		http://lkml.org/lkml/2008/2/8/342

this patch should not be added, I'll get the other one in instead.

thanks,

greg k-h
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