linux-kernel - Re: cpufreq_stats NULL deref on second system suspend

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Message-ID: <5230509D.6040205@linux.vnet.ibm.com>
Date:	Wed, 11 Sep 2013 16:44:37 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Stephen Warren <swarren@...dotorg.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	cpufreq <cpufreq@...r.kernel.org>
Subject: Re: cpufreq_stats NULL deref on second system suspend

On 09/11/2013 04:15 PM, Viresh Kumar wrote:
> On 11 September 2013 16:14, Viresh Kumar <viresh.kumar@...aro.org> wrote:
>> But I would have solved it differently :)
>>
>> We don't really need to call update_policy_cpu() again and again
>> as we don't really need to update policy->cpu...
>>
>> Rather it would be better to just move following inside
>> cpufreq_policy_alloc():
> 
> Half written mail sent :(
> 
> What about moving following to cpufreq_policy_alloc():
> 
> policy->cpu = cpu;
> 
> ??
> 

Hmm? The problem is not about merely updating the policy->cpu field; the
main issue is that the existing code was not letting the cpufreq-stats
code know that we updated the policy->cpu under the hood. It is important
for cpufreq-stats to know this because it maintains the reference to its
stats structure by associating it with the policy->cpu. So if policy->cpu
changes under the hood, it loses track of its reference. So we need to
keep that code informed about changes to policy->cpu. Thus, we need to call
update_policy_cpu() in the CPU online path (during resume). I don't see
how we can skip that.

Regards,
Srivatsa S. Bhat

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