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: <CAKohpomk0GNJcGKxLX3HuaMBgPiSNzFp5BniyNgRbtoLqPm6bQ@mail.gmail.com>
Date:	Mon, 13 Oct 2014 16:13:50 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Prarit Bhargava <prarit@...hat.com>,
	Saravana Kannan <skannan@...eaurora.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lenny Szubowicz <lszubowi@...hat.com>,
	"linux-pm@...r.kernel.org" <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 1 August 2014 22:48, Stephen Boyd <sboyd@...eaurora.org> 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
>
>  ======================================================
>  [ INFO: possible circular locking dependency detected ]
>  3.16.0-rc3-00039-ge1e38f124d87 #47 Not tainted
>  -------------------------------------------------------
>  sh/75 is trying to acquire lock:
>   (s_active#9){++++..}, at: [<c0358a94>] kernfs_remove_by_name_ns+0x3c/0x84

Can you please retry this on mainline? I wasn't able to reproduce it
now over 3.17.
I am trying this on Exynos b.L implementation..
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