linux-kernel - Re: [PATCH v6 2/8] cpufreq: Add boost frequency support in core

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Message-ID: <13618968.iglDI8cQ6h@vostro.rjw.lan>
Date:	Fri, 26 Jul 2013 14:36:08 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Lukasz Majewski <l.majewski@...sung.com>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	Zhang Rui <rui.zhang@...el.com>,
	Eduardo Valentin <eduardo.valentin@...com>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Jonghwa Lee <jonghwa3.lee@...sung.com>,
	Lukasz Majewski <l.majewski@...ess.pl>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Myungjoo Ham <myungjoo.ham@...sung.com>, durgadoss.r@...el.com,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>
Subject: Re: [PATCH v6 2/8] cpufreq: Add boost frequency support in core

On Friday, July 26, 2013 10:33:21 AM Lukasz Majewski wrote:
> On Fri, 26 Jul 2013 12:47:15 +0530 Viresh Kumar wrote,
> > On 25 July 2013 22:03, Lukasz Majewski <l.majewski@...sung.com> wrote:
> > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > 
> > >  /*********************************************************************
> > > + *
> > > BOOST                                              *
> > > +
> > > *********************************************************************/
> > > +static int cpufreq_boost_set_sw(int state) +{
> > > +       struct cpufreq_frequency_table *freq_table;
> > > +       struct cpufreq_policy *policy;
> > > +       int ret = -EINVAL;
> > > +
> > > +       list_for_each_entry(policy, &cpufreq_policy_list,
> > > policy_list) {
> > > +               freq_table =
> > > cpufreq_frequency_get_table(policy->cpu);
> > > +               if (freq_table) {
> > > +                       ret =
> > > cpufreq_frequency_table_cpuinfo(policy,
> > > +                                                       freq_table);
> > > +                       if (!ret) {
> > > +                               policy->user_policy.max =
> > > policy->max;
> > > +                               __cpufreq_governor(policy,
> > > CPUFREQ_GOV_LIMITS);
> > > +                       }
> > > +               }
> > > +       }
> > > +
> > > +       return ret;
> > > +}
> > > +
> > > +int cpufreq_boost_trigger_state(int state)
> > > +{
> > > +       unsigned long flags;
> > > +       int ret = 0;
> > > +
> > > +       if (cpufreq_driver->boost_enabled == state)
> > > +               return 0;
> > > +
> > > +       write_lock_irqsave(&cpufreq_driver_lock, flags);
> > > +       cpufreq_driver->boost_enabled = state;
> > > +       write_unlock_irqrestore(&cpufreq_driver_lock, flags);
> 	    ^^^^^^^^^^^^^^^^^^^^ [*]
> > 
> > Not sure if we should leave the lock at this point of time, as we
> > haven't enabled boost until now.
> 
> The problem here is with the cpufreq_driver->set_boost() call.
> 
> I tried to avoid acquiring lock at one function and release it at
> another (in this case cpufreq_boost_set_sw), especially since the
> __cpufreq_governor() acquires its own lock - good place for deadlock.
> 
> Is it OK for you to grab lock at one function
> (cpufreq_boost_trigger_state()) and then at other function
> (cpufreq_boost_set_sw) release it before calling __cpufreq_governor()
> and grab it again after its completion?

It generally is better to avoid doing that, although it is not unheard of.

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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