linux-kernel - Re: [PATCH 1/2] cpufreq: try to resume policies which failed on last resume

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Date:	Fri, 03 Jan 2014 12:55:29 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"cpufreq\@vger.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm\@vger.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] cpufreq: try to resume policies which failed on last resume

Viresh Kumar <viresh.kumar@...aro.org> writes:

> On 3 January 2014 15:23, Bjørn Mork <bjorn@...k.no> wrote:
>> Note that "ondemand" and "1401000" are the default vaules, so I don't
>> actually change anything here.  The write is causing the problem, not
>> the value.  As expected, I guess.
>>
>> Also note that boot vs non-boot cpu doesn't seem to matter.  Nor does
>> cancelling the hibernation.  The warning appears on hibernate - not on
>> resume.
>
> Hmm... I spent quite some time understanding whats going on and really
> couldn't get across anything as of now. I haven't tried reproducing it though.
>
> Few things that I can make out of this mail chain so far:
> - Apart from the log, everything is working fine. i.e. system is back in
> working condition.

Correct. And users not running a lock debugging kernel will of course
not even see the warning.

> - It only happens when cpufreq_add_dev() fails during hibernation while
> we enable non-boot CPUs again to save image to disk. So, isn't a problem
> for a system which doesn't have any issues with add_dev() failing on
> hibernation

Wrong.  This was my initial assumption but I later found out that the
issue is unrelated to hibernation failures.  Sorry about the confusion.

> - There is a contention of locks in the order they are taken. And the contention
> looks to be between, hotplug lock taken by cpu_online_cpus() and s_active
> lock for sysfs files. Don't know what's the role of previous write to
> sysfs files.
> As that should finish before hibernation starts and so all locks should be back
> in place.

Yes, that seems logical.  But I guess this is where it fails?



Bjørn
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