linux-kernel - Re: [RFC PATCH] cpufreq/hotplug: Fix cpu-hotplug cpufreq race conditions

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Message-ID: <20150602062724.GF10443@linux>
Date:	Tue, 2 Jun 2015 11:57:24 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc:	rjw@...ysocki.net, ego@...ux.vnet.ibm.com, paulus@...ba.org,
	linux-kernel@...r.kernel.org, shilpa.bhat@...ux.vnet.ibm.com,
	linux-pm@...r.kernel.org
Subject: Re: [RFC PATCH] cpufreq/hotplug: Fix cpu-hotplug cpufreq race
 conditions

On 02-06-15, 11:50, Preeti U Murthy wrote:
>  CPU0                        CPU1
> 
> store*                     store*
> 
> lock(policy 1)              lock(policy 2)
> cpufreq_set_policy()       cpufreq_set_policy()
> EXIT() :
> dbs-data->usage_count--
> 
> INIT()                      EXIT()

When will INIT() follow EXIT() in set_policy() for the same governor ?
Maybe not, and so this sequence is hypothetical ?

> dbs_data exists             dbs_data->usage_count -- = 0
>                             kfree(dbs_data)
> dbs-data->usage_count++
> *NULL dereference*

But even if this happens, it should be handled with
dbs_data->mutex_lock, which is used at other places already.

-- 
viresh
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