linux-kernel - Re: [PATCH v3 03/14] sched/core: uclamp: add CPU's clamp groups accounting

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Message-ID: <ccd9c53f-55f7-a285-39eb-4303888dafcd@arm.com>
Date:   Wed, 15 Aug 2018 12:59:54 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v3 03/14] sched/core: uclamp: add CPU's clamp groups
 accounting

On 08/15/2018 12:54 PM, Patrick Bellasi wrote:
> On 15-Aug 11:37, Dietmar Eggemann wrote:
>> On 08/14/2018 06:49 PM, Patrick Bellasi wrote:
>>> Hi Dietmar!
>>>
>>> On 14-Aug 17:44, Dietmar Eggemann wrote:
>>>> On 08/06/2018 06:39 PM, Patrick Bellasi wrote:

[..]

>> If this is only for testing/debugging, I would suggest a simple one line
>> BUG_ON()
> 
> These are (eventually) considered as recoverable errors... thus,
> AFAIK, using BUG_ON is overkilling and discouraged:
>    https://elixir.bootlin.com/linux/latest/source/include/asm-generic/bug.h#L42

Not sure about that. If this refcounting is out of sync, that's 
indicating a serious issue here for me which should be fixed.

>> You find CONFIG_SCHED_DEBUG=y in production kernels as well.
> 
> AFAIK, that setting is discouraged for production kernels...
> Moreover, it's still better to WARN sometimes on a production kernel
> the crash the device, isnt't it?

IMHO, if this is something which should not happen at all, a BUG_ON() is 
the right thing to do here. And you get the call stack to investigate 
why it hit.