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Date: Wed, 20 Nov 2013 13:08:25 +0100
From: Stanislaw Gruszka <sgruszka@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Christian Engelmayer <cengelma@gmx.at>, Ingo Molnar <mingo@redhat.com>,
        linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        fweisbec@gmail.com, Paul Turner <pjt@google.com>
Subject: Re: [PROBLEM] possible divide by 0 in kernel/sched/cputime.c
 scale_stime()
Message-ID: <20131120120815.GA12860@redhat.com>
References: <20131116223740.3cd579cb@spike>
 <20131118140224.GA3330@redhat.com>
 <20131118172706.GI3866@twins.programming.kicks-ass.net>
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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