linux-kernel - Re: [PROBLEM] possible divide by 0 in kernel/sched/cputime.c scale

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Message-ID: <20131120120815.GA12860@redhat.com>
Date:	Wed, 20 Nov 2013 13:08:25 +0100
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Christian Engelmayer <cengelma@....at>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>, fweisbec@...il.com,
	Paul Turner <pjt@...gle.com>
Subject: Re: [PROBLEM] possible divide by 0 in kernel/sched/cputime.c
 scale_stime()

On Mon, Nov 18, 2013 at 06:27:06PM +0100, Peter Zijlstra wrote:
> The below is a compile tested only attempt to deal with both these
> problems. Comments?

Just two nits as I don't understand vast of the patch.

> +	delta_exec = now - curr->exec_start;
> +	if ((s64)delta_exec < 0)
>  		return;

Check here should probably use <= and also unlikely() would be
reasonable. 

> +	schedstat_set(curr->statistics.exec_max,
> +		      max((u64)delta_exec, curr->statistics.exec_max));

(u64) cast not needed.

Stanislaw
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