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

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Message-ID: <54c4aa198131420d9c77542bad5d27e7@baidu.com>
Date: Mon, 16 Jun 2025 11:46:25 +0000
From: "Li,Rongqing" <lirongqing@...du.com>
To: "mingo@...hat.com" <mingo@...hat.com>, "peterz@...radead.org"
	<peterz@...radead.org>, "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"dietmar.eggemann@....com" <dietmar.eggemann@....com>, "rostedt@...dmis.org"
	<rostedt@...dmis.org>, "bsegall@...gle.com" <bsegall@...gle.com>,
	"mgorman@...e.de" <mgorman@...e.de>, "vschneid@...hat.com"
	<vschneid@...hat.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: 答复: [PATCH] sched/cputime: Fix a mostly theoretical divide by zero

> 
> 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>


Ping

Thanks

-Li

> ---
>  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