From: Al Viro <viro@ZenIV.linux.org.uk>
To: Yuri Tikhonov <yur@emcraft.com>
Cc: Wolfgang Denk <wd@denx.de>, Detlev Zundel <dzu@denx.de>,
linux-kernel@vger.kernel.org, Milton Miller <miltonm@bga.com>,
linuxppc-dev@ozlabs.org,
Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>,
Ilya Yanok <yanok@emcraft.com>
Subject: Re: [PATCH] fork_init: fix division by zero
Date: Wed, 10 Dec 2008 10:17:45 +0000 [thread overview]
Message-ID: <20081210101745.GG28946@ZenIV.linux.org.uk> (raw)
In-Reply-To: <503391615.20081210130113@emcraft.com>
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.
WARNING: multiple messages have this Message-ID (diff)
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Yuri Tikhonov <yur@emcraft.com>
Cc: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>,
linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org,
Detlev Zundel <dzu@denx.de>, Wolfgang Denk <wd@denx.de>,
Milton Miller <miltonm@bga.com>, Ilya Yanok <yanok@emcraft.com>
Subject: Re: [PATCH] fork_init: fix division by zero
Date: Wed, 10 Dec 2008 10:17:45 +0000 [thread overview]
Message-ID: <20081210101745.GG28946@ZenIV.linux.org.uk> (raw)
In-Reply-To: <503391615.20081210130113@emcraft.com>
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.
next prev parent reply other threads:[~2008-12-10 10:17 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-12-09 17:44 [PATCH] fork_init: fix division by zero Yuri Tikhonov
2008-12-09 17:44 ` Yuri Tikhonov
2008-12-10 8:44 ` Geert Uytterhoeven
2008-12-10 8:44 ` Geert Uytterhoeven
2008-12-10 10:01 ` Re[2]: " Yuri Tikhonov
2008-12-10 10:01 ` Yuri Tikhonov
2008-12-10 10:17 ` Al Viro [this message]
2008-12-10 10:17 ` Al Viro
2008-12-10 10:29 ` Re[2]: " Yuri Tikhonov
2008-12-10 10:29 ` Yuri Tikhonov
2008-12-10 13:06 ` David Howells
2008-12-10 13:06 ` David Howells
2008-12-10 13:09 ` David Howells
2008-12-10 13:09 ` David Howells
2008-12-10 13:15 ` Geert Uytterhoeven
2008-12-10 13:15 ` Geert Uytterhoeven
2008-12-10 13:25 ` Re[4]: " Yuri Tikhonov
2008-12-10 13:25 ` Yuri Tikhonov
2008-12-10 21:50 ` Re[2]: " Paul Mackerras
2008-12-10 21:50 ` Paul Mackerras
2008-12-10 17:25 ` Scott Wood
2008-12-10 17:25 ` Scott Wood
2008-12-10 17:56 ` Re[2]: " Yuri Tikhonov
2008-12-10 17:56 ` Yuri Tikhonov
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