linux-kernel - Re: [PATCH v2] lib: gcd: prevent possible div by 0

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Message-Id: <20120912123625.fd09bd60.akpm@linux-foundation.org>
Date:	Wed, 12 Sep 2012 12:36:25 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	dave@....org
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	lkml <linux-kernel@...r.kernel.org>, stable@...r.kernel.org
Subject: Re: [PATCH v2] lib: gcd: prevent possible div by 0

On Wed, 12 Sep 2012 21:20:30 +0200
Davidlohr Bueso <dave@....org> wrote:

> On Wed, 2012-09-12 at 12:10 -0700, Andrew Morton wrote:
> > On Mon, 10 Sep 2012 16:35:19 +0200
> > Davidlohr Bueso <dave@....org> wrote:
> > 
> > > Account for all properties when a and/or b are 0:
> > > gcd(0, 0) = 0
> > > gcd(a, 0) = a
> > > gcd(0, b) = b
> > > 
> > > Cc: stable@...r.kernel.org
> > 
> > Why cc:stable?  If this patch fixes some known problem in the current
> > kernel then that really really should have been described in the
> > changelog.  Always.  Please.
> 
> Ok, I will keep it in mind next time. No known problem (at least that I
> know of), but due to the nature of the potential bug, I thought that it
> was worth adding it to stable.

OK.

I'm not personally averse to fixing such problems in -stable,
particualrly in lib/ code.  After all, people who take -stable kernels
will then change them and add drivers and backport changes from later
kernels, etc.  They might be bitten by such a bug.


I'm scratching my head a bit at the patch though.  What does gcd(0, 13)
mean?  That 0 can be divided by 13 zero times, which is an integer
result?  I wonder why any non-buggy code would do that....
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