linux-kernel - Re: [PATCH v4 06/18] PM: EM: Check if the get_cost() callback is present in em_compute

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Message-ID: <6942961b-a5f6-983a-e5c5-10fa097a907d@arm.com>
Date:   Fri, 29 Sep 2023 09:42:45 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        dietmar.eggemann@....com, rui.zhang@...el.com,
        amit.kucheria@...durent.com, amit.kachhap@...il.com,
        daniel.lezcano@...aro.org, viresh.kumar@...aro.org,
        len.brown@...el.com, pavel@....cz, mhiramat@...nel.org,
        qyousef@...alina.io, wvw@...gle.com
Subject: Re: [PATCH v4 06/18] PM: EM: Check if the get_cost() callback is
 present in em_compute_costs()



On 9/26/23 19:46, Rafael J. Wysocki wrote:
> On Mon, Sep 25, 2023 at 10:11 AM Lukasz Luba <lukasz.luba@....com> wrote:
>>
>> The em_compute_cost() is going to be re-used in runtime modified EM
>> code path. Thus, make sure that this common code is safe and won't
>> try to use the NULL pointer. The former em_compute_cost() didn't have to
>> care about runtime modification code path. The upcoming changes introduce
>> such option, but with different callback. Those two paths which use
>> get_cost() (during first EM registration) or update_power() (during
>> runtime modification) need to be safely handled in em_compute_costs().
> 
> I would just say something like this:
> 
> "Subsequent changes will introduce a case in which cb->get_cost may
> not be set in em_compute_costs(), so add a check to ensure that it is
> not NULL before attempting to dereference it."
> 
> The rest of the changelog is just redundant IMO.
> 

Make sense, thanks, I'll change that.