Date: Sun, 22 Feb 2015 08:58:25 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Andrew Morton <akpm@linux-foundation.org>, Joe Perches <joe@perches.com>,
        Peter Zijlstra <peterz@infradead.org>, Oleg Nesterov <oleg@redhat.com>,
        Vladimir Davydov <vdavydov@parallels.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Kees Cook <keescook@chromium.org>,
        David Rientjes <rientjes@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        "David S. Miller" <davem@davemloft.net>,
        Andy Lutomirski <luto@amacapital.net>,
        Michael Marineau <mike@marineau.org>,
        Aaron Tomlin <atomlin@redhat.com>, Prarit Bhargava <prarit@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>, Jens Axboe <axboe@fb.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Rik van Riel <riel@redhat.com>, Davidlohr Bueso <dave@stgolabs.net>,
        Guenter Roeck <linux@roeck-us.net>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3 v3] kernel/fork.c: avoid division by zero
Message-ID: <20150222075825.GA20626@gmail.com>
References: <20150218122851.d1ae723ff12887f9ab919431@linux-foundation.org>
 <1424557146-29965-1-git-send-email-xypron.glpk@gmx.de>
 <1424557146-29965-2-git-send-email-xypron.glpk@gmx.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1424557146-29965-2-git-send-email-xypron.glpk@gmx.de>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1457
Lines: 41


* Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:

> PAGE_SIZE is not guaranteed to be equal to or less than 8 times the
> THREAD_SIZE.
> 
> E.g. architecture hexagon may have page size 1M and thread size 4096.
> This would lead to a division by zero in the calculation of max_threads.
> 
> With 32-bit calculus there is no solution which delivers valid results
> for all possible combinations of the parameters.
> The code is only called once.
> Hence a 64-bit calculation can be used as solution.
> 
> The calculation of max_threads is moved to a separate function.
> This allows future patches to use the same logic, e.g. when
>  - max_threads is set by writing to /proc/sys/kernel/threads-max
>  - when adding or removing memory.
> 
> Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
> ---
>  kernel/fork.c | 59 ++++++++++++++++++++++++++++++++++++++++++-----------------
>  1 file changed, 42 insertions(+), 17 deletions(-)

So it would be nice to split this patch into two parts: 
first do a patch that splits out a version of 
set_max_threads() that matches current behavior (including 
the bug).

Then a second patch that fixes the bug.

This would make it much easier to review.

Thanks,

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/