linux-kernel - [PATCH v1 1/2] thermal/debugfs: Add missing count increment to thermal_debug_tz_trip

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Date: Mon, 15 Apr 2024 21:02:12 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Lukasz Luba <lukasz.luba@....com>,
 Daniel Lezcano <daniel.lezcano@...aro.org>
Subject:
 [PATCH v1 1/2] thermal/debugfs: Add missing count increment to
 thermal_debug_tz_trip_up()

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

The count field in struct trip_stats, representing the number of times
the zone temperature was above the trip point, needs to be incremented
in thermal_debug_tz_trip_up(), for two reasons.

First, if a trip point is crossed on the way up for the first time,
thermal_debug_update_temp() called from update_temperature() does
not see it because it has not been added to trips_crossed[] array
in the thermal zone's struct tz_debugfs object yet.  Therefore, when
thermal_debug_tz_trip_up() is called after that, the trip point's
count value is 0, and the attempt to divide by it during the average
temperature computation leads to a divide error which causes the kernel
to crash.  Setting the count to 1 before the division by incrementing it
fixes this problem.

Second, if a trip point is crossed on the way up, but it has been
crossed on the way up already before, its count value needs to be
incremented to make a record of the fact that the zone temperature is
above the trip now.  Without doing that, if the mitigations applied
after crossing the trip cause the zone temperature to drop below its
threshold, the count will not be updated for this episode at all and
the average temperature in the trip statistics record will be somewhat
smaller than it should be.

Fixes: 7ef01f228c9f ("thermal/debugfs: Add thermal debugfs information for mitigation episodes")
Cc :6.8+ <stable@...r.kernel.org> # 6.8+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/thermal/thermal_debugfs.c |    1 +
 1 file changed, 1 insertion(+)

Index: linux-pm/drivers/thermal/thermal_debugfs.c
===================================================================
--- linux-pm.orig/drivers/thermal/thermal_debugfs.c
+++ linux-pm/drivers/thermal/thermal_debugfs.c
@@ -616,6 +616,7 @@ void thermal_debug_tz_trip_up(struct the
 	tze->trip_stats[trip_id].timestamp = now;
 	tze->trip_stats[trip_id].max = max(tze->trip_stats[trip_id].max, temperature);
 	tze->trip_stats[trip_id].min = min(tze->trip_stats[trip_id].min, temperature);
+	tze->trip_stats[trip_id].count++;
 	tze->trip_stats[trip_id].avg = tze->trip_stats[trip_id].avg +
 		(temperature - tze->trip_stats[trip_id].avg) /
 		tze->trip_stats[trip_id].count;