linux-kernel - Re: [PATCH] fork_init: fix division by zero

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Message-ID: <20081210101745.GG28946@ZenIV.linux.org.uk>
Date:	Wed, 10 Dec 2008 10:17:45 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Yuri Tikhonov <yur@...raft.com>
Cc:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	Detlev Zundel <dzu@...x.de>, Wolfgang Denk <wd@...x.de>,
	Milton Miller <miltonm@....com>, Ilya Yanok <yanok@...raft.com>
Subject: Re: [PATCH] fork_init: fix division by zero

On Wed, Dec 10, 2008 at 01:01:13PM +0300, Yuri Tikhonov wrote:

> >> +     max_threads = mempages * PAGE_SIZE / (8 * THREAD_SIZE);
> >                       ^^^^^^^^^^^^^^^^^^^^
> >> +#endif
> 
> > Can't this overflow, e.g. on 32-bit machines with HIGHMEM?
> 
>  The multiplier here is not PAGE_SIZE, but [PAGE_SIZE / (8 * 
> THREAD_SIZE)], and this value is expected to be rather small (2, 4, or 
> so).

x * y / z is parsed as (x * y) / z, not x * (y / z).

Only assignment operators (and ?:, in a sense that a ? b : c ? d : e is
parsed as a ? b : (c ? d : e)) are right-to-left.  The rest is left-to-right.
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