linux-kernel - Re: [PATCH v4 RESEND] PM: EM: Fix potential division-by-zero error in em_compute

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Message-ID: <CAJZ5v0hM9KwdHRcoBjGRJq7y6wkQDFt+PMuU1k=3ARifDvOENA@mail.gmail.com>
Date: Mon, 28 Apr 2025 15:30:23 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Yaxiong Tian <iambestgod@...com>
Cc: lukasz.luba@....com, rafael@...nel.org, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Yaxiong Tian <tianyaxiong@...inos.cn>
Subject: Re: [PATCH v4 RESEND] PM: EM: Fix potential division-by-zero error in em_compute_costs()

On Fri, Apr 18, 2025 at 3:19 AM Yaxiong Tian <iambestgod@...com> wrote:
>
> From: Yaxiong Tian <tianyaxiong@...inos.cn>
>
> When the device is of a non-CPU type, table[i].performance won't be
> initialized in the previous em_init_performance(), resulting in division
> by zero when calculating costs in em_compute_costs().
>
> Since the 'cost' algorithm is only used for EAS energy efficiency
> calculations and is currently not utilized by other device drivers, we
> should add the _is_cpu_device(dev) check to prevent this division-by-zero
> issue.
>
> Fixes: 1b600da51073 ("PM: EM: Optimize em_cpu_energy() and remove division")
> Signed-off-by: Yaxiong Tian <tianyaxiong@...inos.cn>
> Reviewed-by: Lukasz Luba <lukasz.luba@....com>
> ---
>  kernel/power/energy_model.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index d9b7e2b38c7a..41606247c277 100644
> --- a/kernel/power/energy_model.c
> +++ b/kernel/power/energy_model.c
> @@ -233,6 +233,10 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
>         unsigned long prev_cost = ULONG_MAX;
>         int i, ret;
>
> +       /* This is needed only for CPUs and EAS skip other devices */
> +       if (!_is_cpu_device(dev))
> +               return 0;
> +
>         /* Compute the cost of each performance state. */
>         for (i = nr_states - 1; i >= 0; i--) {
>                 unsigned long power_res, cost;
> --

Applied as 6.16 material, thanks!