Re: [PATCH v5] mm,writeback: fix divide by zero in pos_ratio_polynom

[Rik van Riel]

On 04/30/2014 05:00 PM, Andrew Morton wrote:
> On Wed, 30 Apr 2014 16:42:55 -0400 Rik van Riel <riel@xxxxxxxxxx> wrote:
>
> > On Wed, 30 Apr 2014 13:13:53 -0700
> > Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> 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!

The more I look at the code, the more I am convinced that
Michal is right, and we cannot actually hit the case that
"limit - setpoint + 1 == 0".

Setpoint always seems to be some in-between point.

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