From: Saravana Kannan <skannan@codeaurora.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Juri Lelli <juri.lelli@arm.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Michael Turquette <mturquette@baylibre.com>,
Steve Muckle <steve.muckle@linaro.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Morten Rasmussen <morten.rasmussen@arm.com>,
dietmar.eggemann@arm.com
Subject: Re: [RFC PATCH 11/19] cpufreq: assert policy->rwsem is held in __cpufreq_governor
Date: Tue, 02 Feb 2016 13:37:21 -0800 [thread overview]
Message-ID: <56B12191.8020407@codeaurora.org> (raw)
In-Reply-To: <20160202063449.GF31828@vireshk>
On 02/01/2016 10:34 PM, Viresh Kumar wrote:
> On 01-02-16, 12:24, Saravana Kannan wrote:
>> On 02/01/2016 02:22 AM, Rafael J. Wysocki wrote:
>> I'm not sure whose idea you are referring to. Viresh's (I don't think I saw
>> his proposal) or mine.
>
> http://git.linaro.org/people/viresh.kumar/linux.git/commit/57714d5b1778f2f610bcc5c74d85b29ba1cc1995
>
>> Anyway, to explain my suggestion better, I'm proposing to make it so that we
>> don't have a need for the AB BA locking. The only reason the governor needs
>> to even grab the sysfs lock is to add/remove the sysfs attribute files.
>>
>> That can be easily achieved if the policy struct has some "gov_attrs"
>> field(s) that each governor populates. Then the framework just has to create
>> them after POLICY_INIT is processed by the governor and remove them before
>> POILICY_EXIT is sent to the governor.
>
> What will that solve? It will stay exactly same then as well, as we
> would be adding/removing these attributes from within the same
> policy->rwsem ..
The problem isn't that you are holding the policy rwsem. The problem is
that we are trying to grab the same locks in different order. This is
trying to fix that.
>
>> That way, we also avoid having to worry about the gov attributes accessed by
>> the show/store disappearing while the files are being accessed.
>
> It can't happen. S_active lock should be taking care of that, isn't
> it?
You are right. That can't happen because we have the s_active lock. I
meant to say that in general we don't have to worry about the races
between a show/store needing some policy specific data within the
governor to be valid but racing with governor change where it ends up
being invalid. The releasing of the policy rwsem across POLICY_EXIT
allows this to happen today.
-Saravana
--
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project
next prev parent reply other threads:[~2016-02-02 21:37 UTC|newest]
Thread overview: 110+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-11 17:35 [RFC PATCH 00/19] cpufreq locking cleanups and documentation Juri Lelli
2016-01-11 17:35 ` [RFC PATCH 01/19] cpufreq: do not expose cpufreq_governor_lock Juri Lelli
2016-01-12 8:56 ` Viresh Kumar
2016-01-11 17:35 ` [RFC PATCH 02/19] cpufreq: merge governor lock and mutex Juri Lelli
2016-01-12 9:00 ` Viresh Kumar
2016-01-11 17:35 ` [RFC PATCH 03/19] cpufreq: kill for_each_policy Juri Lelli
2016-01-12 9:01 ` Viresh Kumar
2016-01-11 17:35 ` [RFC PATCH 04/19] cpufreq: bring data structures close to their locks Juri Lelli
2016-01-11 22:05 ` Peter Zijlstra
2016-01-11 23:03 ` Rafael J. Wysocki
2016-01-12 8:27 ` Peter Zijlstra
2016-01-12 10:43 ` Juri Lelli
2016-01-12 16:47 ` Rafael J. Wysocki
2016-01-11 22:07 ` Peter Zijlstra
2016-01-12 9:27 ` Viresh Kumar
2016-01-12 11:21 ` Juri Lelli
2016-01-12 11:58 ` Peter Zijlstra
2016-01-12 12:36 ` Juri Lelli
2016-01-12 15:26 ` Juri Lelli
2016-01-12 15:58 ` Peter Zijlstra
2016-01-12 9:10 ` Viresh Kumar
2016-01-11 17:35 ` [RFC PATCH 05/19] cpufreq: assert locking when accessing cpufreq_policy_list Juri Lelli
2016-01-12 9:34 ` Viresh Kumar
2016-01-12 11:44 ` Juri Lelli
2016-01-13 5:59 ` Viresh Kumar
2016-01-11 17:35 ` [RFC PATCH 06/19] cpufreq: always access cpufreq_policy_list while holding cpufreq_driver_lock Juri Lelli
2016-01-12 9:57 ` Viresh Kumar
2016-01-12 12:08 ` Juri Lelli
2016-01-13 6:01 ` Viresh Kumar
2016-01-11 17:35 ` [RFC PATCH 07/19] cpufreq: assert locking when accessing cpufreq_governor_list Juri Lelli
2016-01-12 10:01 ` Viresh Kumar
2016-01-12 15:33 ` Juri Lelli
2016-01-11 17:35 ` [RFC PATCH 08/19] cpufreq: fix warning for cpufreq_init_policy unlocked access to cpufreq_governor_list Juri Lelli
2016-01-12 10:09 ` Viresh Kumar
2016-01-12 15:52 ` Juri Lelli
2016-01-13 6:07 ` Viresh Kumar
2016-01-14 16:35 ` Juri Lelli
2016-01-18 5:23 ` Viresh Kumar
2016-01-18 15:19 ` Juri Lelli
2016-01-11 17:35 ` [RFC PATCH 09/19] cpufreq: fix warning for show_scaling_available_governors " Juri Lelli
2016-01-12 10:13 ` Viresh Kumar
2016-01-13 10:25 ` Juri Lelli
2016-01-13 10:32 ` Viresh Kumar
2016-01-11 17:35 ` [RFC PATCH 10/19] cpufreq: assert policy->rwsem is held in cpufreq_set_policy Juri Lelli
2016-01-12 10:15 ` Viresh Kumar
2016-01-11 17:35 ` [RFC PATCH 11/19] cpufreq: assert policy->rwsem is held in __cpufreq_governor Juri Lelli
2016-01-12 10:20 ` Viresh Kumar
2016-01-30 0:33 ` Saravana Kannan
2016-01-30 11:49 ` Rafael J. Wysocki
2016-02-01 6:09 ` Viresh Kumar
2016-02-01 10:22 ` Rafael J. Wysocki
2016-02-01 20:24 ` Saravana Kannan
2016-02-01 21:00 ` Rafael J. Wysocki
2016-02-02 6:36 ` Viresh Kumar
2016-02-02 21:38 ` Saravana Kannan
2016-02-02 6:34 ` Viresh Kumar
2016-02-02 21:37 ` Saravana Kannan [this message]
2016-02-03 2:13 ` Viresh Kumar
2016-02-03 4:04 ` Saravana Kannan
2016-02-03 5:02 ` Viresh Kumar
2016-02-03 5:06 ` Saravana Kannan
2016-02-03 6:59 ` Viresh Kumar
2016-01-11 17:35 ` [RFC PATCH 12/19] cpufreq: fix locking of policy->rwsem in cpufreq_init_policy Juri Lelli
2016-01-12 10:39 ` Viresh Kumar
2016-01-14 17:58 ` Juri Lelli
2016-01-11 17:35 ` [RFC PATCH 13/19] cpufreq: fix locking of policy->rwsem in cpufreq_offline_prepare Juri Lelli
2016-01-12 10:54 ` Viresh Kumar
2016-01-15 12:37 ` Juri Lelli
2016-01-11 17:35 ` [RFC PATCH 14/19] cpufreq: fix locking of policy->rwsem in cpufreq_offline_finish Juri Lelli
2016-01-12 11:02 ` Viresh Kumar
2016-01-11 17:35 ` [RFC PATCH 15/19] cpufreq: remove useless usage of cpufreq_governor_mutex in __cpufreq_governor Juri Lelli
2016-01-12 11:06 ` Viresh Kumar
2016-01-15 16:30 ` Juri Lelli
2016-01-18 5:50 ` Viresh Kumar
2016-01-19 16:49 ` Juri Lelli
2016-01-20 7:29 ` Viresh Kumar
2016-01-20 10:17 ` Juri Lelli
2016-01-20 10:18 ` Viresh Kumar
2016-01-20 10:27 ` Juri Lelli
2016-01-20 10:30 ` Viresh Kumar
2016-01-11 17:35 ` [RFC PATCH 16/19] cpufreq: hold policy->rwsem across CPUFREQ_GOV_POLICY_EXIT Juri Lelli
2016-01-12 11:09 ` Viresh Kumar
2016-01-11 17:35 ` [RFC PATCH 17/19] cpufreq: stop checking for cpufreq_driver being present in cpufreq_cpu_get Juri Lelli
2016-01-12 11:17 ` Viresh Kumar
2016-01-11 17:35 ` [RFC PATCH 18/19] cpufreq: remove transition_lock Juri Lelli
2016-01-12 11:24 ` Viresh Kumar
2016-01-13 0:54 ` Michael Turquette
2016-01-13 6:31 ` Viresh Kumar
[not found] ` <20160113182131.1168.45753@quark.deferred.io>
2016-01-14 9:44 ` Juri Lelli
2016-01-14 10:32 ` Viresh Kumar
2016-01-14 13:52 ` Juri Lelli
2016-01-18 5:09 ` Viresh Kumar
2016-01-19 14:00 ` Peter Zijlstra
2016-01-19 14:42 ` Juri Lelli
2016-01-19 15:30 ` Peter Zijlstra
2016-01-19 16:01 ` Juri Lelli
2016-01-19 19:17 ` Peter Zijlstra
2016-01-19 19:21 ` Peter Zijlstra
2016-01-19 21:52 ` Rafael J. Wysocki
2016-01-20 17:04 ` Peter Zijlstra
2016-01-20 22:12 ` Rafael J. Wysocki
2016-01-20 22:38 ` Peter Zijlstra
2016-01-20 23:33 ` Rafael J. Wysocki
2016-01-20 12:59 ` Juri Lelli
2016-01-11 17:36 ` [RFC PATCH 19/19] cpufreq: documentation: document locking scheme Juri Lelli
2016-01-11 22:45 ` [RFC PATCH 00/19] cpufreq locking cleanups and documentation Rafael J. Wysocki
2016-01-12 10:46 ` Juri Lelli
2016-01-30 0:57 ` Saravana Kannan
2016-02-01 6:02 ` Viresh Kumar
2016-02-01 12:06 ` Juri Lelli
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