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From: Greg KH <gregkh@suse.de>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Yi Yang <yi.y.yang@intel.com>,
	akpm@linux-foundation.org, davej@codemonkey.org.uk,
	cpufreq@lists.linux.org.uk, linux-kernel@vger.kernel.org,
	linux-acpi@vger.kernel.org, mingo@elte.hu,
	torvalds@linux-foundation.org,
	linux-pm@lists.linux-foundation.org
Subject: Re: [linux-pm] [PATCH 2.6.25-rc1] cpufreq: fix cpufreq policy refcount imbalance
Date: Fri, 15 Feb 2008 10:24:21 -0800	[thread overview]
Message-ID: <20080215182421.GA5593@suse.de> (raw)
In-Reply-To: <Pine.LNX.4.44L0.0802151043230.3423-100000@iolanthe.rowland.org>

On Fri, Feb 15, 2008 at 10:52:51AM -0500, Alan Stern wrote:
> 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.

There's the additional problem that this second reference count is never
dropped, causing a bug :)

thanks,

greg k-h

  reply	other threads:[~2008-02-15 18:26 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-04 10:10 [linux-pm][PATCH] base: Change power/wakeup output from "" to "unsupported" if wakeup feature isn't supported by a device Yi Yang
2008-01-04 11:48 ` Pavel Machek
2008-01-04 16:09   ` David Brownell
2008-01-04 16:38     ` Alan Stern
2008-01-04 16:52       ` Olivier Galibert
2008-01-04 17:20         ` Oliver Neukum
2008-01-07  2:00           ` Yi Yang
2008-01-07  1:55         ` Yi Yang
2008-01-07  3:49           ` David Brownell
2008-01-07  1:52       ` Yi Yang
2008-01-07  1:37     ` Yi Yang
2008-01-07  1:57       ` Rafael J. Wysocki
2008-01-07  2:05         ` Yi Yang
2008-01-07 16:46           ` Rafael J. Wysocki
2008-01-07  1:21   ` Yi Yang
2008-01-04 16:31 ` David Brownell
2008-01-07  1:51   ` Yi Yang
2008-01-22 23:05 ` [PATCH 2.6.24-rc8] cpufreq: fix obvious condition statement error Yi Yang
2008-01-28 23:14   ` [PATCH 2.6.24] x86: add sysfs interface for cpuid module Yi Yang
2008-01-29  8:44     ` Sam Ravnborg
2008-01-29 22:22       ` Yi Yang
2008-01-30  7:48         ` Sam Ravnborg
2008-01-29 15:51     ` H. Peter Anvin
2008-01-29 17:52       ` Yi Yang
2008-01-30  6:09         ` H. Peter Anvin
2008-01-29 21:56       ` Yi Yang
2008-01-30  7:17         ` H. Peter Anvin
2008-01-29 22:13           ` Yi Yang
2008-01-30  7:33             ` H. Peter Anvin
2008-01-29 23:41     ` [RFC PATCH 2.6.24] x86: add sysfs interface for cpuid module, try 2 Yi Yang
2008-01-30 17:35       ` H. Peter Anvin
2008-01-31  1:18       ` [PATCH 2.6.24] Add new string functions real_strtoul and change kernel params to use them Yi Yang
2008-01-31 17:03         ` Randy Dunlap
2008-01-31 16:30           ` Yi Yang
2008-02-01  2:47             ` Randy Dunlap
2008-01-31 22:11         ` [PATCH 2.6.24] Add new string functions strict_strto* and convert kernel params to use them, take 2 Yi Yang
2008-02-01  0:02           ` [PATCH 2.6.24] Add new string functions strict_strto* and convert kernel params to use them, take 3 Yi Yang
2008-02-01  7:36           ` [PATCH 2.6.24] Add new string functions strict_strto* and convert kernel params to use them, take 2 Andrew Morton
2008-02-01  7:39           ` Andrew Morton
2008-02-01  7:40           ` Andrew Morton
2008-02-01 16:31     ` [PATCH 2.6.24] x86: add sysfs interface for cpuid module dean gaudet
2008-02-01 17:56       ` H. Peter Anvin
2008-02-01 17:58         ` H. Peter Anvin
2008-02-14 23:44   ` [PATCH 2.6.25-rc1] cpufreq: fix cpufreq policy refcount imbalance Yi Yang
2008-02-14 23:48   ` Yi Yang
2008-02-15 15:52     ` [linux-pm] " Alan Stern
2008-02-15 18:24       ` Greg KH [this message]
2008-02-15 21:01     ` Greg KH
2008-02-25  0:46     ` [PATCH 2.6.25-rc3] cpuidle: fix cpuidle time and usage overflow Yi Yang
2008-02-25 10:15       ` Ingo Molnar
2008-02-25  1:10         ` Yi Yang
2008-03-26  4:46       ` Len Brown

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