linux-kernel - Re: [PATCH v1 5/7] thermal: add trace events to the power allocator governor

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Date:	Mon, 2 Feb 2015 15:44:50 +0000
From:	Javi Merino <javi.merino@....com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Punit Agrawal <Punit.Agrawal@....com>,
	"broonie@...nel.org" <broonie@...nel.org>,
	Zhang Rui <rui.zhang@...el.com>,
	Eduardo Valentin <edubezval@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v1 5/7] thermal: add trace events to the power allocator
 governor

On Wed, Jan 28, 2015 at 05:31:06PM +0000, Steven Rostedt wrote:
> On Wed, 28 Jan 2015 17:00:36 +0000
> Javi Merino <javi.merino@....com> wrote:
> 
> > +	if (trace_thermal_power_cpu_limit_enabled() && load_cpu) {
> > +		trace_thermal_power_cpu_get_power(
> > +			&cpufreq_device->allowed_cpus,
> > +			freq, load_cpu, i, dynamic_power, static_power);
> > +
> > +		devm_kfree(&cdev->device, load_cpu);
> 
> You may want to move the devm_kfree() out of the
> trace_thermal_power_cpu_limit_enabled() check. There could be a race
> where that gets disabled while this function is running and you just
> leaked memory.
> 
> 	if (load_cpu)
> 		devm_kfree(&cdev->device, load_cpu);
> 
> should be done by itself.

Good catch!  I've changed it to 

	if (load_cpu) {
		trace_thermal_power_cpu_get_power(
			&cpufreq_device->allowed_cpus,
			freq, load_cpu, i, dynamic_power, static_power);

		devm_kfree(&cdev->device, load_cpu);
	}

This way, if the trace is disabled while in the function,
trace_thermal_power_cpu_get_power() doesn't get executed but you free
load_cpu.  If the opposite happens (the trace gets enabled while in
the function), load_cpu is NULL and you don't pass the NULL pointer to
trace_thermal_power_cpu_get_power().

Cheers,
Javi
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