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

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Message-ID: <20131118153941.GA28699@gmail.com>
Date:	Mon, 18 Nov 2013 16:39:41 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Stanislaw Gruszka <sgruszka@...hat.com>,
	Christian Engelmayer <cengelma@....at>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PROBLEM] possible divide by 0 in kernel/sched/cputime.c
 scale_stime()


* Peter Zijlstra <peterz@...radead.org> wrote:

> I would be tempted to say you should simply mark the tsc unstable on 
> boot and live with that -- we fully assume the sched_clock stuff is 
> not going backwards in an 'observable' way.

BIOS crap and actual hardware bugs do happen - so kernel code needs to 
consider TSC input with a pinch of salt, assuming that it's untrusted 
external data.

> That said, it might be nice to not crash either..

Indeed, not crashing on weird TSC input is absolutely required!

Thanks,

	Ingo
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