From: Saravana Kannan <skannan@codeaurora.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Prarit Bhargava" <prarit@redhat.com>,
"Stephen Boyd" <sboyd@codeaurora.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Lenny Szubowicz" <lszubowi@redhat.com>,
"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
"Robert Schöne" <robert.schoene@tu-dresden.de>
Subject: Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem to be held for duration of changing governors [v2]
Date: Mon, 04 Aug 2014 13:16:37 -0700 [thread overview]
Message-ID: <53DFEA25.5070206@codeaurora.org> (raw)
In-Reply-To: <CAKohpomEQ__Q4xTaBgHJyE0Meu4au-cXKCAKCqHWTHLRL+R5OA@mail.gmail.com>
On 08/04/2014 06:38 AM, Viresh Kumar wrote:
> On 4 August 2014 17:55, Prarit Bhargava <prarit@redhat.com> wrote:
>> The issue is the collision between the setup & teardown of the policy's governor
>> sysfs files.
>>
>> On creation the kernel does:
>>
>> down_write(&policy->rwsem)
>> mutex_lock(kernfs_mutex) <- note this is similar to the "old" sysfs_mutex.
>>
>> The opposite happens on a governor switch, specifically the existing governor's
>> exit, and then we get a lockdep warning.
>
> Okay, probably a bit more clarity is what I was looking for. Suppose we try
> to change governor, now tell me what will happen.
>
Viresh, I have a good understanding of what's going on. I was planning
to fix this after the rest of my patches are done. Didn't want to keep
too many outstanding unaccepted patches.
The problem is when between one thread trying to cat a governor's file
(say, sampling_rate) vs the governor getting a POLICY_EXIT.
In the read thread, the sysfs lock is grabbed first and then the policy
lock is grabbed next. When the governor gets the POLICY_EXIT, we call it
with the policy lock held and the governor tries to do sysfs remove
which tries to grab the sysfs lock. Classic deadlock.
Could you please look at my policy free/remove patches? If you can do
that, I can work on a fix for this. It might also be simpler to fix
after my patch series (not sure, might be).
Thanks,
Saravana
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
hosted by The Linux Foundation
next prev parent reply other threads:[~2014-08-04 20:16 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-29 11:46 [PATCH] cpufreq, store_scaling_governor requires policy->rwsem to be held for duration of changing governors [v2] Prarit Bhargava
2014-07-30 0:03 ` Rafael J. Wysocki
2014-07-30 14:18 ` Prarit Bhargava
2014-07-30 21:40 ` Rafael J. Wysocki
2014-07-31 1:36 ` Saravana Kannan
2014-07-31 2:16 ` Rafael J. Wysocki
2014-07-31 2:07 ` Saravana Kannan
2014-07-31 10:16 ` Prarit Bhargava
2014-07-31 10:21 ` Prarit Bhargava
2014-07-31 10:23 ` Prarit Bhargava
2014-07-31 16:36 ` Rafael J. Wysocki
2014-07-31 17:57 ` Prarit Bhargava
2014-07-31 18:38 ` Rafael J. Wysocki
2014-07-31 18:26 ` Prarit Bhargava
2014-07-31 20:24 ` Saravana Kannan
2014-07-31 20:30 ` Prarit Bhargava
2014-07-31 20:38 ` Saravana Kannan
2014-07-31 21:08 ` Prarit Bhargava
2014-07-31 22:13 ` Saravana Kannan
2014-07-31 22:58 ` Prarit Bhargava
2014-08-01 0:55 ` Saravana Kannan
2014-08-01 10:24 ` Prarit Bhargava
2014-08-01 10:27 ` Prarit Bhargava
2014-08-01 17:18 ` Stephen Boyd
2014-08-01 19:15 ` Prarit Bhargava
2014-08-01 19:36 ` Stephen Boyd
2014-08-01 19:43 ` Prarit Bhargava
2014-08-01 19:54 ` Stephen Boyd
2014-08-01 21:25 ` Saravana Kannan
2014-08-04 10:11 ` Prarit Bhargava
2014-08-05 7:46 ` Viresh Kumar
2014-08-05 10:47 ` Prarit Bhargava
2014-08-05 10:53 ` Viresh Kumar
2014-08-05 22:06 ` Saravana Kannan
2014-08-05 22:20 ` Prarit Bhargava
2014-08-05 22:40 ` Saravana Kannan
2014-08-05 22:42 ` Prarit Bhargava
2014-08-05 22:51 ` Saravana Kannan
2014-08-13 19:57 ` Prarit Bhargava
2014-08-13 19:57 ` Prarit Bhargava
2014-08-14 18:16 ` Saravana Kannan
2014-08-14 18:16 ` Saravana Kannan
2014-08-06 8:10 ` Viresh Kumar
2014-08-06 10:09 ` Prarit Bhargava
2014-08-06 10:09 ` Prarit Bhargava
2014-08-06 15:08 ` Stephen Boyd
2014-08-07 6:36 ` Viresh Kumar
2014-08-07 10:12 ` Prarit Bhargava
2014-08-07 10:15 ` Viresh Kumar
2014-08-12 9:03 ` Viresh Kumar
2014-08-12 11:33 ` Prarit Bhargava
2014-08-13 7:39 ` Viresh Kumar
2014-08-13 9:58 ` Prarit Bhargava
2014-08-13 9:58 ` Prarit Bhargava
2014-08-14 4:19 ` Viresh Kumar
2014-08-04 10:36 ` Viresh Kumar
2014-08-04 12:25 ` Prarit Bhargava
2014-08-04 13:38 ` Viresh Kumar
2014-08-04 14:00 ` Prarit Bhargava
2014-08-04 15:04 ` Prarit Bhargava
2014-08-04 20:16 ` Saravana Kannan [this message]
2014-08-05 6:14 ` Viresh Kumar
2014-08-05 6:29 ` skannan
2014-08-05 6:43 ` Viresh Kumar
2014-10-13 10:43 ` Viresh Kumar
2014-10-13 11:52 ` Prarit Bhargava
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