From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f200.google.com (mail-qt0-f200.google.com [209.85.216.200]) by kanga.kvack.org (Postfix) with ESMTP id AD3866B0260 for ; Wed, 12 Oct 2016 03:22:14 -0400 (EDT) Received: by mail-qt0-f200.google.com with SMTP id g45so30993912qte.5 for ; Wed, 12 Oct 2016 00:22:14 -0700 (PDT) Received: from sender153-mail.zoho.com (sender153-mail.zoho.com. [74.201.84.153]) by mx.google.com with ESMTPS id v18si1751238qtv.57.2016.10.12.00.22.13 for (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 12 Oct 2016 00:22:14 -0700 (PDT) Subject: Re: [RFC PATCH 1/1] mm/percpu.c: fix memory leakage issue when allocate a odd alignment area References: <20161011172228.GA30403@dhcp22.suse.cz> <7649b844-cfe6-abce-148e-1e2236e7d443@zoho.com> <20161012065332.GA9504@dhcp22.suse.cz> From: zijun_hu Message-ID: <57FDE42C.8040808@zoho.com> Date: Wed, 12 Oct 2016 15:20:12 +0800 MIME-Version: 1.0 In-Reply-To: <20161012065332.GA9504@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, zijun_hu@htc.com, tj@kernel.org, akpm@linux-foundation.org, cl@linux.com On 10/12/2016 02:53 PM, Michal Hocko wrote: > On Wed 12-10-16 08:28:17, zijun_hu wrote: >> On 2016/10/12 1:22, Michal Hocko wrote: >>> On Tue 11-10-16 21:24:50, zijun_hu wrote: >>>> From: zijun_hu >>>> >>>> the LSB of a chunk->map element is used for free/in-use flag of a area >>>> and the other bits for offset, the sufficient and necessary condition of >>>> this usage is that both size and alignment of a area must be even numbers >>>> however, pcpu_alloc() doesn't force its @align parameter a even number >>>> explicitly, so a odd @align maybe causes a series of errors, see below >>>> example for concrete descriptions. >>> >>> Is or was there any user who would use a different than even (or power of 2) >>> alighment? If not is this really worth handling? >>> >> >> it seems only a power of 2 alignment except 1 can make sure it work very well, >> that is a strict limit, maybe this more strict limit should be checked > > I fail to see how any other alignment would actually make any sense > what so ever. Look, I am not a maintainer of this code but adding a new > code to catch something that doesn't make any sense sounds dubious at > best to me. > > I could understand this patch if you see a problem and want to prevent > it from repeating bug doing these kind of changes just in case sounds > like a bad idea. > thanks for your reply should we have a generic discussion whether such patches which considers many boundary or rare conditions are necessary. should we make below declarations as conventions 1) when we say 'alignment', it means align to a power of 2 value for example, aligning value @v to @b implicit @v is power of 2 , align 10 to 4 is 12 2) when we say 'round value @v up/down to boundary @b', it means the result is a times of @b, it don't requires @b is a power of 2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org