linux-kernel - Re: [PATCH v5] mm,writeback: fix divide by zero in pos_ratio

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Message-Id: <20140430140057.7d2a6e984b2ec987182d2a4e@linux-foundation.org>
Date:	Wed, 30 Apr 2014 14:00:57 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	Michal Hocko <mhocko@...e.cz>,
	Masayoshi Mizuma <m.mizuma@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	sandeen@...hat.com, jweiner@...hat.com,
	kosaki.motohiro@...fujitsu.com, fengguang.wu@...el.com,
	mpatlasov@...allels.com, Motohiro.Kosaki@...fujitsu.com
Subject: Re: [PATCH v5] mm,writeback: fix divide by zero in
 pos_ratio_polynom

On Wed, 30 Apr 2014 16:42:55 -0400 Rik van Riel <riel@...hat.com> wrote:

> On Wed, 30 Apr 2014 13:13:53 -0700
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > This was a consequence of 64->32 truncation and it can't happen any
> > more, can it?
> 
> Andrew, this is cleaner indeed :)

I'm starting to get worried about 32-bit wraparound in the patch
version number ;)

> Masayoshi-san, does the bug still happen with this version, or does
> this fix the problem?
> 

We could put something like

	if (WARN_ON_ONCE(setpoint == limit))
		setpoint--;

in there if we're not sure.  But it's better to be sure!


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