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

Greg KH
2008-02-15T18:24:21Z

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