linux-kernel - Re: [PATCH]cpuidle: preventive check in cpuidle

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Message-ID: <20171227015722.GA3413@gaurav.jindal>
Date:   Wed, 27 Dec 2017 07:27:22 +0530
From:   gaurav jindal <gauravjindal1104@...il.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH]cpuidle: preventive check in cpuidle_select against crash

On Wed, Dec 27, 2017 at 01:42:58AM +0100, Rafael J. Wysocki wrote:
> On Tue, Dec 26, 2017 at 8:26 AM, gaurav jindal
> <gauravjindal1104@...il.com> wrote:
> > When selecting the idle state using cpuidle_select, there is no
> > check on cpuidle_curr_governor. In cpuidle_switch_governor,
> > cpuidle_currr_governor can be set to NULL to specify "disabled".
> 
> How exactly?

In cpuidle_switch_governor:
 
/**
 * cpuidle_switch_governor - changes the governor
 * @gov: the new target governor
 *
 * NOTE: "gov" can be NULL to specify disabled
 * Must be called with cpuidle_lock acquired.
 */
int cpuidle_switch_governor(struct cpuidle_governor *gov)
{
	struct cpuidle_device *dev;

	if (gov == cpuidle_curr_governor)
		return 0;

	cpuidle_uninstall_idle_handler();

	if (cpuidle_curr_governor) {
		list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
			cpuidle_disable_device(dev);
	}

	cpuidle_curr_governor = gov;

This allows to set the cpuidle_switch_governor as NULL. Although there is no
current code flow leading here, but it has a potential for bug in future. So
may be better to have prevention.