From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg KH Subject: Re: [linux-pm] [PATCH 2.6.25-rc1] cpufreq: fix cpufreq policy refcount imbalance Date: Fri, 15 Feb 2008 10:24:21 -0800 Message-ID: <20080215182421.GA5593@suse.de> References: <1203032921.3897.10.camel@yangyi-dev.bj.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Alan Stern Cc: Yi Yang , 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 List-Id: linux-acpi@vger.kernel.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