linux-kernel - Re: [PATCH 2/4 v4] kernel/fork.c: avoid division by zero

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Message-ID: <20150223211002.GG5029@twins.programming.kicks-ass.net>
Date:	Mon, 23 Feb 2015 22:10:02 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Heinrich Schuchardt <xypron.glpk@....de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Aaron Tomlin <atomlin@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Davidlohr Bueso <dave@...olabs.net>,
	David Rientjes <rientjes@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Fabian Frederick <fabf@...net.be>,
	Guenter Roeck <linux@...ck-us.net>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Jens Axboe <axboe@...com>, Joe Perches <joe@...ches.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Kees Cook <keescook@...omium.org>,
	Michael Marineau <mike@...ineau.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vladimir Davydov <vdavydov@...allels.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4 v4] kernel/fork.c: avoid division by zero

On Mon, Feb 23, 2015 at 09:14:35PM +0100, Heinrich Schuchardt wrote:
> With 32-bit calculus there is no solution which delivers valid results
> for all possible combinations of the parameters.

So I can't help but be bugged by this (my problem I know); calculus is
the mathematics of change; its differential equations and integrals.

What we do here is modular arithmetic on a commutative ring.

Please use calculation as you do here:

> Hence a 64-bit calculation can be used as solution.

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