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Message-ID: <20150222075825.GA20626@gmail.com>
Date: Sun, 22 Feb 2015 08:58:25 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Heinrich Schuchardt <xypron.glpk@....de>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Joe Perches <joe@...ches.com>,
Peter Zijlstra <peterz@...radead.org>,
Oleg Nesterov <oleg@...hat.com>,
Vladimir Davydov <vdavydov@...allels.com>,
Thomas Gleixner <tglx@...utronix.de>,
Kees Cook <keescook@...omium.org>,
David Rientjes <rientjes@...gle.com>,
Johannes Weiner <hannes@...xchg.org>,
"David S. Miller" <davem@...emloft.net>,
Andy Lutomirski <luto@...capital.net>,
Michael Marineau <mike@...ineau.org>,
Aaron Tomlin <atomlin@...hat.com>,
Prarit Bhargava <prarit@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>,
Jens Axboe <axboe@...com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Rik van Riel <riel@...hat.com>,
Davidlohr Bueso <dave@...olabs.net>,
Guenter Roeck <linux@...ck-us.net>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3 v3] kernel/fork.c: avoid division by zero
* Heinrich Schuchardt <xypron.glpk@....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@....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
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