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

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Date:	Wed, 22 Jul 2015 12:42:40 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	Rafael Wysocki <rjw@...ysocki.net>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	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 22-07-15, 01:15, Rafael J. Wysocki wrote:
> So the problem is that the cpu_is_offline(cpu) check in
> cpufreq_add_dev() matches two distinct cases: (1) the CPU was not
> present before and it is just being hot-added and (2) the CPU is
> initially offline, but present, and this is the first time its device
> is registered.  In the first case we can expect that the CPU will
> become online shortly (although that is not guaranteed too), but in
> the second case that very well may not happen.

Yeah.

> We need to be able to distinguish between those two cases and your
> patch does that, but I'm not sure if this really is the most
> straightforward way to do it.

Maybe yeah. I will take another look into that after considering
Russell's input.

> I'm also unsure why you're changing the removal code paths.  Is there
> any particular failure scenario you're concerned about?

The same issue is present here too. The problem was that cpu_offline()
check was getting hit for a CPU that is present in related_cpus mask.
While allocating/freeing the policy, we create links for all
related_cpus and the cpu_offline() check was adding/removing the link
again.

-- 
viresh
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