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Date: Tue, 17 Feb 2015 10:56:36 +0300
From: Vladimir Davydov <vdavydov@parallels.com>
To: Heinrich Schuchardt <xypron.glpk@gmx.de>
CC: Andrew Morton <akpm@linux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Oleg Nesterov <oleg@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        David Rientjes <rientjes@google.com>,
        Kees Cook <keescook@chromium.org>, Aaron Tomlin <atomlin@redhat.com>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/1] kernel/fork.c: avoid division by zero
Message-ID: <20150217075636.GJ28367@esperanza>
References: <1424109644-22579-1-git-send-email-xypron.glpk@gmx.de>
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On Mon, Feb 16, 2015 at 07:00:44PM +0100, Heinrich Schuchardt wrote:
> diff --git a/kernel/fork.c b/kernel/fork.c
> index cf65139..71e2583 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -273,7 +273,8 @@ void __init fork_init(unsigned long mempages)
>  	 * value: the thread structures can take up at most half
>  	 * of memory.
>  	 */
> -	max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
> +	max_threads = (u64) PAGE_SIZE * (u64) mempages
> +		    / (u64) THREAD_SIZE / 8UL;

This won't compile for a 32 bit arch, will it? Should you use div_u64?

Thanks,
Vladimir