linux-kernel - Re: [PATCH] acpi-cpufreq: Skip cleanup if initialization didn't occur

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Date:   Mon, 07 Jun 2021 09:13:14 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     kyle.meyer@....com, rjw@...ysocki.net,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-acpi@...r.kernel.org, Takashi Iwai <tiwai@...e.com>
Subject: Re: [PATCH] acpi-cpufreq: Skip cleanup if initialization didn't occur

On Mon, 07 Jun 2021 05:25:50 +0200,
Viresh Kumar wrote:
> 
> On 04-06-21, 12:05, kyle.meyer@....com wrote:
> > From: Kyle Meyer <kyle.meyer@....com>
> > 
> > acpi-cpufreq is loaded without performing initialization when a cpufreq
> > driver exists.
> > 
> > If initialization didn't occur then skip cleanup in acpi_cpufreq_exit().
> > This prevents unnecessary freeing and unregistering when the module is
> > unloaded.
> > 
> > Reported-by: Takashi Iwai <tiwai@...e.com>
> > Signed-off-by: Kyle Meyer <kyle.meyer@....com>
> > ---
> >  drivers/cpufreq/acpi-cpufreq.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
> > index 7e7450453714..8d425f14c267 100644
> > --- a/drivers/cpufreq/acpi-cpufreq.c
> > +++ b/drivers/cpufreq/acpi-cpufreq.c
> > @@ -1042,8 +1042,19 @@ static int __init acpi_cpufreq_init(void)
> >  
> >  static void __exit acpi_cpufreq_exit(void)
> >  {
> > +	const char *current_driver;
> > +
> >  	pr_debug("%s\n", __func__);
> >  
> > +	/*
> > +	 * If another cpufreq_driver was loaded, preventing acpi-cpufreq from
> > +	 * registering, there's no need to unregister it.
> > +	 */
> > +	current_driver = cpufreq_get_current_driver();
> > +	if (!current_driver ||
> > +	    strncmp(current_driver, acpi_cpufreq_driver.name, strlen(acpi_cpufreq_driver.name)))
> > +		return;
> > +
> >  	acpi_cpufreq_boost_exit();
> >  
> >  	cpufreq_unregister_driver(&acpi_cpufreq_driver);
> 
> Looks like some misunderstanding here, this shouldn't happen. If
> initialization didn't occur, then exit shall never be called.

The missing key information is that it's a fix for the recent change
for 5.14, i.e. 
Fixes: c1d6d2fd2f64 ("cpufreq: acpi-cpufreq: Skip initialization if cpufreq driver is present")

The change made the module left even if it exits before registering
the cpufreq driver object.


Takashi