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

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Message-ID: <tencent_7F99ED4767C1AF7889D0D8AD50F34859CE06@qq.com>
Date: Fri, 18 Apr 2025 09:06:13 +0800
From: Yaxiong Tian <iambestgod@...com>
To: lukasz.luba@....com,
	rafael@...nel.org
Cc: linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Yaxiong Tian <tianyaxiong@...inos.cn>
Subject: [PATCH v4 RESEND] PM: EM: Fix potential division-by-zero error in em_compute_costs()

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;
-- 
2.25.1