linux-kernel - Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem to be held for duration of changing governors [v2]

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Date:	Fri, 01 Aug 2014 15:43:35 -0400
From:	Prarit Bhargava <prarit@...hat.com>
To:	Stephen Boyd <sboyd@...eaurora.org>
CC:	Saravana Kannan <skannan@...eaurora.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-kernel@...r.kernel.org,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Lenny Szubowicz <lszubowi@...hat.com>, linux-pm@...r.kernel.org
Subject: Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem
 to be held for duration of changing governors [v2]



On 08/01/2014 03:36 PM, Stephen Boyd wrote:
> On 08/01/14 12:15, Prarit Bhargava wrote:
>>
>> On 08/01/2014 01:18 PM, Stephen Boyd wrote:
>>> On 08/01/14 03:27, Prarit Bhargava wrote:
>>>> Can you send me the test and the trace of the deadlock?  I'm not creating it with:
>>>>
>>> This was with conservative as the default, and switching to ondemand
>>>
>>> # cd /sys/devices/system/cpu/cpu2/cpufreq
>>> # ls
>>> affected_cpus                  scaling_available_governors
>>> conservative                   scaling_cur_freq
>>> cpuinfo_cur_freq               scaling_driver
>>> cpuinfo_max_freq               scaling_governor
>>> cpuinfo_min_freq               scaling_max_freq
>>> cpuinfo_transition_latency     scaling_min_freq
>>> related_cpus                   scaling_setspeed
>>> scaling_available_frequencies  stats
>>> # cat conservative/down_threshold
>>> 20
>>> # echo ondemand > scaling_governor
>> Thanks Stephen,
>>
>> There's obviously a difference in our .configs.  I have a global conservative
>> directory, ie) /sys/devices/system/cpu/cpufreq/conservative instead of a per-cpu
>> governor file.
>>
>> ie) what are your .config options for CPUFREQ?
>>
>> Mine are:
>>
>> #
>> # CPU Frequency scaling
>> #
>> CONFIG_CPU_FREQ=y
>> CONFIG_CPU_FREQ_GOV_COMMON=y
>> CONFIG_CPU_FREQ_STAT=m
>> CONFIG_CPU_FREQ_STAT_DETAILS=y
>> # CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE is not set
>> # CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE is not set
>> # CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND is not set
>> CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE=y
>> CONFIG_CPU_FREQ_GOV_PERFORMANCE=y
>> CONFIG_CPU_FREQ_GOV_POWERSAVE=y
>> CONFIG_CPU_FREQ_GOV_USERSPACE=y
>> CONFIG_CPU_FREQ_GOV_ONDEMAND=y
>> CONFIG_CPU_FREQ_GOV_CONSERVATIVE=y
>>
>> Is there some other config option I have to set?
> 
> I have the same options. The difference is that my driver has a governor
> per policy. That's set with the CPUFREQ_HAVE_GOVERNOR_PER_POLICY flag.
> If I remove that flag I can't trigger the lockdep splat anymore with
> this sequence and your patch.

I see -- so you're seeing this on arm then?  If so, let me know so I can reserve
one to work on :)

Thanks!

P.
> 
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