linux-kernel - Re: [PATCH] cpufreq: Avoid double addition/removal of sysfs links

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Date:	Wed, 22 Jul 2015 12:34:48 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Rafael Wysocki <rjw@...ysocki.net>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: Avoid double addition/removal of sysfs links

On 21-07-15, 03:14, Rafael J. Wysocki wrote:
> That said, cpu_present_mask may only be updated after calling
> arch_unregister_cpu(), so checking it in cpufreq_remove_dev() doesn't
> really help.

No, it is indeed useful. This is a snippet from the latest code we
have:

		cpumask_copy(&mask, policy->related_cpus);
		cpumask_clear_cpu(cpu, &mask);

		/*
		 * Free policy only if all policy->related_cpus are removed
		 * physically.
		 */
		if (cpumask_intersects(&mask, cpu_present_mask)) {
			remove_cpu_dev_symlink(policy, cpu);
			return 0;
		}

		cpufreq_policy_free(policy, true);



So what we are checking in the 'if' block is: "Is any CPU from
related_cpus, apart from the one getting removed now, present in the
system."

If not, then free the policy.

> It looks like using cpufreq_remove_dev() as the subsys ->remove_dev
> callback is a mistake as it cannot really tell the difference between
> that code path and the CPU offline one.

What do you mean by this? Doesn't the sif parameter confirms that its
called from subsys path ?

-- 
viresh
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