linux-kernel - [PATCH] sched/cputime: Fix a mostly theoretical divide by zero

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Message-ID: <20250604110442.8251-1-lirongqing@baidu.com>
Date: Wed, 4 Jun 2025 19:04:42 +0800
From: lirongqing <lirongqing@...du.com>
To: <mingo@...hat.com>, <peterz@...radead.org>, <juri.lelli@...hat.com>,
	<vincent.guittot@...aro.org>, <dietmar.eggemann@....com>,
	<rostedt@...dmis.org>, <bsegall@...gle.com>, <mgorman@...e.de>,
	<vschneid@...hat.com>, <linux-kernel@...r.kernel.org>
CC: Li RongQing <lirongqing@...du.com>
Subject: [PATCH] sched/cputime: Fix a mostly theoretical divide by zero

From: Li RongQing <lirongqing@...du.com>

Sum of utime and stime can overflow to 0, when a process with
many threads run over total 2^64 ns

Signed-off-by: Li RongQing <lirongqing@...du.com>
---
 kernel/sched/cputime.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 6dab4854..c35fc4c 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -579,7 +579,8 @@ void cputime_adjust(struct task_cputime *curr, struct prev_cputime *prev,
 		goto update;
 	}
 
-	stime = mul_u64_u64_div_u64(stime, rtime, stime + utime);
+	if (likely(stime + utime))
+		stime = mul_u64_u64_div_u64(stime, rtime, stime + utime);
 	/*
 	 * Because mul_u64_u64_div_u64() can approximate on some
 	 * achitectures; enforce the constraint that: a*b/(b+c) <= a.
-- 
2.9.4