linux-kernel - Re: [PATCH] PM / OPP: cpufreq: Avoid sleeping while atomic

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Message-ID: <CAKohpon5787nmLO02=UtSkQZY=p3F_xZ0_E-tu+psME_UoWdHQ@mail.gmail.com>
Date:	Fri, 18 Jul 2014 09:32:06 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Kevin Hilman <khilman@...prootsystems.com>,
	Nishanth Menon <nm@...com>
Subject: Re: [PATCH] PM / OPP: cpufreq: Avoid sleeping while atomic

On 18 July 2014 04:57, Stephen Boyd <sboyd@...eaurora.org> wrote:
> First you need to enable sleeping while atomic checking, but in reality,
> I assume nobody has tried inserting a cpufreq driver as a module. The

I did for sure, but long back. Over 6 months atleast :)

> might_sleep() code has a check to see if the system_state is
> SYSTEM_RUNNING. If it isn't running then there isn't a warning and
> might_sleep() doesn't flag any problem. I wonder if that is actually the
> right thing to do though? Perhaps the intention of that code is to skip
> warning early on in the boot path when the scheduler isn't up and
> running yet. But once the scheduler is running (which is fairly early
> nowadays) I would think we want might_sleep() to trigger warnings. Maybe
> that check in might_sleep() needs to be updated to check for "scheduler
> running" instead of "system running"?
> Right. It seems that we moved to RCU in commit
> 0f5c890e9b9754d9aa5bf6ae2fc00cae65780d23 so the real Fixes line should be:
>
> Fixes: 0f5c890e9b97 "PM / OPP: Remove cpufreq wrapper dependency on
> internal data organization"

Right.

> One way to avoid this problem is to put things back the way they were
> before that change. Is there any real benefit to having this code live
> in drivers/cpufreq/ instead of just under some config option in
> drivers/base/power/opp.c?

Maybe Nishanth can give more arguments than I can :), but the idea was
just to keep cpufreq stuff together..
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