linux-kernel - Re: [PATCH] cpufreq: imx6: prorect calls to dev_pm_opp_get_opp

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Message-ID: <CAE_wzQ_J088FOzBoq66irs4A=ShJ3rqzLmT2sEP6dmvPE6cB2w@mail.gmail.com>
Date:	Mon, 15 Dec 2014 21:41:03 -0800
From:	Dmitry Torokhov <dtor@...omium.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Dmitry Torokhov <dtor@...omium.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Shawn Guo <shawn.guo@...escale.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Anson Huang <b20788@...escale.com>,
	John Tobias <john.tobias.ph@...il.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: imx6: prorect calls to dev_pm_opp_get_opp_count
 with RCU lock

On Mon, Dec 15, 2014 at 9:33 PM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> On 16 December 2014 at 06:20, Dmitry Torokhov <dtor@...omium.org> wrote:
>> dev_pm_opp_get_opp_count() must be called with RCU lock held.
>>
>> Signed-off-by: Dmitry Torokhov <dtor@...omium.org>
>> ---
>>
>> Not tested at all...
>>
>>  drivers/cpufreq/imx6q-cpufreq.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/cpufreq/imx6q-cpufreq.c b/drivers/cpufreq/imx6q-cpufreq.c
>> index 380a90d..851d4fd 100644
>> --- a/drivers/cpufreq/imx6q-cpufreq.c
>> +++ b/drivers/cpufreq/imx6q-cpufreq.c
>> @@ -200,7 +200,9 @@ static int imx6q_cpufreq_probe(struct platform_device *pdev)
>>          * Just, incase the platform did not supply the OPP
>>          * table, it will try to get it.
>>          */
>> +       rcu_read_lock();
>>         num = dev_pm_opp_get_opp_count(cpu_dev);
>> +       rcu_read_unlock();
>>         if (num < 0) {
>>                 ret = of_init_opp_table(cpu_dev);
>>                 if (ret < 0) {
>> @@ -211,7 +213,9 @@ static int imx6q_cpufreq_probe(struct platform_device *pdev)
>>                 /* Because we have added the OPPs here, we must free them */
>>                 free_opp = true;
>>
>> +               rcu_read_lock();
>>                 num = dev_pm_opp_get_opp_count(cpu_dev);
>> +               rcu_read_unlock();
>>                 if (num < 0) {
>>                         ret = num;
>>                         dev_err(cpu_dev, "no OPP table is found: %d\n", ret);
>
> This one looks fine for sure but I was wondering for the users which just
> need to call opp-count from under the locks, what about something like:
>
> dev_pm_opp_get_opp_count_locked() ?

Yeah, for the majority of callers taking the lock won't hurt as they
call it in their init code.

Thanks,
Dmitry
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