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

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Date:	Fri, 15 Feb 2008 10:52:51 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Yi Yang <yi.y.yang@...el.com>
cc:	akpm@...ux-foundation.org, <davej@...emonkey.org.uk>,
	<cpufreq@...ts.linux.org.uk>, <gregkh@...e.de>,
	<linux-kernel@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
	<mingo@...e.hu>, <torvalds@...ux-foundation.org>,
	<linux-pm@...ts.linux-foundation.org>
Subject: Re: [linux-pm] [PATCH 2.6.25-rc1] cpufreq: fix cpufreq policy refcount
 imbalance

On Fri, 15 Feb 2008, Yi Yang wrote:

> 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.

Are you referring to this section of code (before the region affected 
by your patch)?

	if (!kobject_get(&data->kobj)) {
		spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
		cpufreq_debug_enable_ratelimit();
		unlock_policy_rwsem_write(cpu);
		return -EFAULT;
	}

Greg is correct that the kobject_get() here is useless and should be
removed.  kobject_get() never returns NULL unless its argument is NULL.  
Since &data->kobj can never be NULL, the "if" test will never fail.  
Hence there's no point in making the test at all.

The fact that a section of code has existed for a long time doesn't 
mean that it is right.  :-)

Furthermore, there's no reason to do the kobject_get().  Holding 2 
references to a kobject is no better than holding just 1 reference.  
Assuming you know that the kobject is still registered, then you also 
know that there is already a reference to it.  So you have no reason to 
take an additional reference.

Alan Stern

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