linux-kernel - [PATCH] cpuidle: teo: fix underflow of recent intercepts

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Date: Sun, 19 May 2024 22:03:59 +0100
From: Christian Loehle <christian.loehle@....com>
To: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rafael@...nel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: Qais Yousef <qyousef@...alina.io>, kajetan.puchalski@....com,
 Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: [PATCH] cpuidle: teo: fix underflow of recent intercepts

The recent counter of each cpuidle state bin reflects the number of
recent intercepts. It's decremented and incremented accordingly.
The decrement was never checked for 0, therefore underflowing into a
value teo cannot easily recover from.

The underflow lead to deeper idle states being skipped because teo
assumed interception was likely and it preferring shallower states.

Fixes: 77577558f25d ("cpuidle: teo: Rework most recent idle duration values treatment")
Signed-off-by: Christian Loehle <christian.loehle@....com>
---
 drivers/cpuidle/governors/teo.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/cpuidle/governors/teo.c b/drivers/cpuidle/governors/teo.c
index 7244f71c59c5..42fb2771e35d 100644
--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -290,7 +290,8 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 	if (cpu_data->next_recent_idx >= NR_RECENT)
 		cpu_data->next_recent_idx = 0;

-	if (cpu_data->recent_idx[i] >= 0)
+	if (cpu_data->recent_idx[i] >= 0 &&
+			cpu_data->state_bins[cpu_data->recent_idx[i]].recent)
 		cpu_data->state_bins[cpu_data->recent_idx[i]].recent--;

 	/*
-- 
2.34.1