From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753966AbbBPStu (ORCPT ); Mon, 16 Feb 2015 13:49:50 -0500 Received: from bh-25.webhostbox.net ([208.91.199.152]:37833 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752986AbbBPStt (ORCPT ); Mon, 16 Feb 2015 13:49:49 -0500 Message-ID: <54E23BC7.6070802@roeck-us.net> Date: Mon, 16 Feb 2015 10:49:43 -0800 From: Guenter Roeck User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Heinrich Schuchardt , Andrew Morton CC: "Kirill A. Shutemov" , Oleg Nesterov , Peter Zijlstra , Ingo Molnar , Vladimir Davydov , Thomas Gleixner , David Rientjes , Kees Cook , Aaron Tomlin , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] kernel/fork.c: avoid division by zero References: <1424109644-22579-1-git-send-email-xypron.glpk@gmx.de> <54E23AD2.9060703@gmx.de> In-Reply-To: <54E23AD2.9060703@gmx.de> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated_sender: linux@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-CTCH-PVer: 0000001 X-CTCH-Spam: Unknown X-CTCH-VOD: Unknown X-CTCH-Flags: 0 X-CTCH-RefID: str=0001.0A020204.54E23BCC.01A5,ss=1,re=0.001,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0 X-CTCH-Score: 0.001 X-CTCH-ScoreCust: 0.000 X-CTCH-Rules: C_4847, X-CTCH-SenderID: linux@roeck-us.net X-CTCH-SenderID-Flags: 0 X-CTCH-SenderID-TotalMessages: 1 X-CTCH-SenderID-TotalSpam: 0 X-CTCH-SenderID-TotalSuspected: 0 X-CTCH-SenderID-TotalConfirmed: 0 X-CTCH-SenderID-TotalBulk: 0 X-CTCH-SenderID-TotalVirus: 0 X-CTCH-SenderID-TotalRecipients: 0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: mailgid no entry from get_relayhosts_entry X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/16/2015 10:45 AM, Heinrich Schuchardt wrote: > I am resending this mail because the linux-kernel list was not CCed. > Yes, sorry, that got lost. The "forward" feature on lkml.org doesn't work as well as it used to, unfortunately, and I keep forgetting. > On 16.02.2015 19:23, Guenter Roeck wrote: >> On Mon, Feb 16, 2015 at 07:00:44PM +0100, Heinrich Schuchardt 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. >>> >>> Signed-off-by: Heinrich Schuchardt >>> --- >>> kernel/fork.c | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> 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; >> >> How about >> max_threads = mempages / (8 * THREAD_SIZE) * PAGE_SIZE; >> >> instead ? That would avoid the u64. > > We have to consider the case mempages < 8 * THREAD_SIZE. > > Let > mempages = 1024 > THREAD_SIZE = 4096 > PAGE_SIZE = 1M > > Your code gives 0. > Mine gives 8192. > Makes sense. Thanks, Guenter