[PATCH v4 RESEND] PM: EM: Fix potential division-by-zero error in em_compute_costs()

[PATCH v4 RESEND] PM: EM: Fix potential division-by-zero error in em_compute_costs()

[Yaxiong Tian]

From: Yaxiong Tian <tianyaxiong@kylinos.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@kylinos.cn>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.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;
-- 
2.25.1

Re: [PATCH v4 RESEND] PM: EM: Fix potential division-by-zero error in em_compute_costs()

[Rafael J. Wysocki]

On Fri, Apr 18, 2025 at 3:19 AM Yaxiong Tian <iambestgod@qq.com> wrote:
>
> From: Yaxiong Tian <tianyaxiong@kylinos.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@kylinos.cn>
> Reviewed-by: Lukasz Luba <lukasz.luba@arm.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!