linux-kernel - Re: [Patch v3 7/7] sched: thermal: Enable tuning of decay period

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Message-ID: <20191015101452.GA237548@google.com>
Date:   Tue, 15 Oct 2019 11:14:52 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     Thara Gopinath <thara.gopinath@...aro.org>
Cc:     mingo@...hat.com, peterz@...radead.org, ionela.voinescu@....com,
        vincent.guittot@...aro.org, rui.zhang@...el.com,
        edubezval@...il.com, linux-kernel@...r.kernel.org,
        amit.kachhap@...il.com, javi.merino@...nel.org,
        daniel.lezcano@...aro.org
Subject: Re: [Patch v3 7/7] sched: thermal: Enable tuning of decay period

Hi Thara,

On Sunday 13 Oct 2019 at 20:58:25 (-0400), Thara Gopinath wrote:
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 00fcea2..5056c08 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -376,6 +376,13 @@ static struct ctl_table kern_table[] = {
>  		.mode		= 0644,
>  		.proc_handler	= proc_dointvec,
>  	},
> +	{
> +		.procname	= "sched_thermal_decay_coeff",
> +		.data		= &sysctl_sched_thermal_decay_coeff,
> +		.maxlen		= sizeof(unsigned int),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec,

Perhaps change this for 'sched_proc_update_handler' with min and max
values ? Otherwise userspace is allowed to write nonsensical values
here. And since sysctl_sched_thermal_decay_coeff is used to shift, this
can lead to an undefined behaviour.

Also, could we take this sysctl out of SCHED_DEBUG ? I expect this to be
used/tuned on production devices where SCHED_DEBUG should theoretically
be off.

Thanks,
Quentin