From: Paul Mackerras <paulus@samba.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: wd@denx.de, dzu@denx.de, linux-kernel@vger.kernel.org,
miltonm@bga.com, linuxppc-dev@ozlabs.org,
Geert.Uytterhoeven@sonycom.com, yanok@emcraft.com,
viro@zeniv.linux.org.uk
Subject: Re: [PATCH][v2] fork_init: fix division by zero
Date: Fri, 12 Dec 2008 11:48:29 +1100 [thread overview]
Message-ID: <18753.46301.944770.779390@cargo.ozlabs.ibm.com> (raw)
In-Reply-To: <20081211121635.ff58193f.akpm@linux-foundation.org>
Andrew Morton writes:
> > +#if (8 * THREAD_SIZE) > PAGE_SIZE
> > max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
> > +#else
> > + max_threads = mempages * (PAGE_SIZE / (8 * THREAD_SIZE));
> > +#endif
>
> The expression you've chosen here can be quite inacccurate, because
> ((PAGE_SIZE / (8 * THREAD_SIZE)) is a small number. The way to
> preserve accuracy is
The assumption is that THREAD_SIZE is a power of 2, as is PAGE_SIZE.
I think Yuri should be increasing THREAD_SIZE for the larger page
sizes he's implementing, because we have on-stack arrays whose size
depends on the page size. I suspect that having THREAD_SIZE less than
1/8 of PAGE_SIZE risks stack overflows, and the better fix is for Yuri
to make sure THREAD_SIZE is at least 1/8 of PAGE_SIZE. (In fact, more
may be needed - someone should work out what fraction is actually
needed.)
Paul.
next prev parent reply other threads:[~2008-12-12 0:48 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-12-10 16:50 [PATCH][v2] fork_init: fix division by zero Yuri Tikhonov
2008-12-11 20:16 ` Andrew Morton
2008-12-11 20:28 ` Al Viro
2008-12-11 20:43 ` Andrew Morton
2008-12-12 2:31 ` Nick Piggin
2008-12-12 2:47 ` Andrew Morton
2008-12-12 3:36 ` Nick Piggin
2008-12-11 22:22 ` Re[2]: " Yuri Tikhonov
2008-12-11 22:26 ` Andrew Morton
2008-12-12 0:48 ` Paul Mackerras [this message]
2008-12-12 1:07 ` Andrew Morton
2008-12-18 7:47 ` Yuri Tikhonov
2008-12-18 22:45 ` Andrew Morton
2008-12-19 5:49 ` Re[2]: " Yuri Tikhonov
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