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

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Message-ID: <53DBEC27.7050803@codeaurora.org>
Date:	Fri, 01 Aug 2014 12:36:07 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Prarit Bhargava <prarit@...hat.com>
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 08/01/14 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.

-- 
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