linux-kernel - Re: [PATCH v2 2/7] cpufreq/sched: Move cpufreq-specific EAS checks to cpufreq

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Message-ID: <70cadfd8-8d5c-4685-b3d0-23cde6edc522@arm.com>
Date: Mon, 12 May 2025 19:24:35 +0200
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
 Marek Szyprowski <m.szyprowski@...sung.com>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>,
 Linux PM <linux-pm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
 Lukasz Luba <lukasz.luba@....com>, Peter Zijlstra <peterz@...radead.org>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
 Morten Rasmussen <morten.rasmussen@....com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
 Pierre Gondois <pierre.gondois@....com>,
 Christian Loehle <christian.loehle@....com>
Subject: Re: [PATCH v2 2/7] cpufreq/sched: Move cpufreq-specific EAS checks to
 cpufreq

On 12/05/2025 14:53, Rafael J. Wysocki wrote:
> On Mon, May 12, 2025 at 8:48 AM Marek Szyprowski
> <m.szyprowski@...sung.com> wrote:
>>
>> On 10.05.2025 13:31, Rafael J. Wysocki wrote:
>>> On Sat, May 10, 2025 at 1:49 AM Marek Szyprowski
>>> <m.szyprowski@...sung.com> wrote:
>>>> On 06.05.2025 22:37, Rafael J. Wysocki wrote:
>>>>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

[...]

>>>>    *** DEADLOCK ***
>>> Well, it turns out that trying to acquire policy->rwsem under
>>> sched_domains_mutex is a bad idea.  It was added to
>>> cpufreq_policy_is_good_for_eas() to address a theoretical race, so it
>>> can be dropped safely.  A theoretical race is better than a real
>>> deadlock.
>>>
>>> Please test the attached patch.
>>
>> This fixed the observed issue. Thanks!
>>
>> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
>> Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
> 
> Thanks for the confirmation!

See this on my Hikey 960 as well. I was wondering why Christian L. and I
didn't catch this with RFT v1.0 (*) on i7-13700K.

But it looks like that

https://web.git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/log/?h=experimental/intel_pstate/eas-take2-extended

mentioned in the patch-header of (*) didn't have this line in its

commit 9ad047cade6b ("cpufreq/sched: Move cpufreq-specific EAS checks to
cpufreq")