linux-kernel - Re: [PATCH V3] powercap/drivers/idle_injection: Add an idle injection framework

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Date:   Wed, 23 May 2018 15:19:07 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     rjw@...ysocki.net, edubezval@...il.com, kevin.wangtao@...aro.org,
        leo.yan@...aro.org, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org, javi.merino@...nel.org,
        rui.zhang@...el.com, linux-pm@...r.kernel.org,
        daniel.thompson@...aro.org
Subject: Re: [PATCH V3] powercap/drivers/idle_injection: Add an idle injection
 framework

On 23/05/2018 11:55, Viresh Kumar wrote:
> On 23-05-18, 10:00, Daniel Lezcano wrote:

[ ... ]

> Maybe I wasn't able to explain the problem I see, but lemme retry
> that. Assume that there is only one use and that id cpu-idle-cooling.
> We are currently running the idle loop with idle duration X and run
> duration Y.
> 
> Now lets say the cooling device gets unregistered itself (maybe module
> removal, etc). And it calls idle_injection_unregister() with a valid
> pointer. Not sure if the thermal framework will call set_cur_state
> anymore. But the problem will remain even if it does that.
> 
> We call idle_injection_stop() from unregister, which will cancel
> hrtimer, set durations as 0 and return. Then we free the iidev. It is
> certainly possible at this point of time that the kthread is still
> running the idle loop which it may have started before unregister was
> called. And so after the idle loop is finished it will try to access
> ii_dev, which is already freed.
> 
> So, idle_injection_stop() needs to guarantee that the kthread and the
> hrtimer are all stopped now and no one is using the ii_dev structure
> anymore.
> 
> Perhaps you need some completion stuff here to give confirmation here,
> etc.

Ok, let me come back with something.

Thanks for reviewing again.

  -- Daniel



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