linux-kernel - [PATCH] watchdog/softlockup: Fix sample ring index wrap in need_counting

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Message-ID: <tencent_08C319B2F9CDBDCAD20B0D380C4CDB7CF406@qq.com>
Date: Sun, 18 Jan 2026 17:14:49 +0800
From: "shengminghu512" <shengminghu512@...com>
To: "broonie" <broonie@...nel.org>
Cc: "linux-kernel" <linux-kernel@...r.kernel.org>, "hu.shengming" <hu.shengming@....com.cn>, "zhang.run" <zhang.run@....com.cn>
Subject: [PATCH] watchdog/softlockup: Fix sample ring index wrap in need_counting_irqs()

From: Shengming Hu <hu.shengming@....com.cn>

cpustat_tail indexes cpustat_util[], which is a NUM_SAMPLE_PERIODS-sized
ring buffer. need_counting_irqs() currently wraps the index using
NUM_HARDIRQ_REPORT, which only happens to match NUM_SAMPLE_PERIODS.

Use NUM_SAMPLE_PERIODS for the wrap to keep the ring math correct even if
the NUM_HARDIRQ_REPORT or  NUM_SAMPLE_PERIODS changes.

Signed-off-by: Shengming Hu <hu.shengming@....com.cn>
---
 kernel/watchdog.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index b4d5fbdb9..7d675781b 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -550,7 +550,7 @@ static bool need_counting_irqs(void)
 	u8 util;
 	int tail = __this_cpu_read(cpustat_tail);
 
-	tail = (tail + NUM_HARDIRQ_REPORT - 1) % NUM_HARDIRQ_REPORT;
+	tail = (tail + NUM_SAMPLE_PERIODS - 1) % NUM_SAMPLE_PERIODS;
 	util = __this_cpu_read(cpustat_util[tail][STATS_HARDIRQ]);
 	return util > HARDIRQ_PERCENT_THRESH;
 }
-- 
2.25.1