From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id CFA006B0069 for ; Thu, 13 Oct 2016 19:31:42 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id i85so92614934pfa.5 for ; Thu, 13 Oct 2016 16:31:42 -0700 (PDT) Received: from mail-pf0-x244.google.com (mail-pf0-x244.google.com. [2607:f8b0:400e:c00::244]) by mx.google.com with ESMTPS id m3si12768391pgd.262.2016.10.13.16.31.42 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 13 Oct 2016 16:31:42 -0700 (PDT) Received: by mail-pf0-x244.google.com with SMTP id i85so2527162pfa.0 for ; Thu, 13 Oct 2016 16:31:42 -0700 (PDT) Date: Thu, 13 Oct 2016 19:31:39 -0400 From: Tejun Heo Subject: Re: [RFC PATCH 1/1] mm/percpu.c: fix memory leakage issue when allocate a odd alignment area Message-ID: <20161013233139.GE32534@mtj.duckdns.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: zijun_hu Cc: akpm@linux-foundation.org, zijun_hu@htc.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cl@linux.com On Tue, Oct 11, 2016 at 09:24:50PM +0800, 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. > > lets assume area [16, 36) is free but its previous one is in-use, we want > to allocate a @size == 8 and @align == 7 area. the larger area [16, 36) is > split to three areas [16, 21), [21, 29), [29, 36) eventually. however, due > to the usage for a chunk->map element, the actual offset of the aim area > [21, 29) is 21 but is recorded in relevant element as 20; moreover the > residual tail free area [29, 36) is mistook as in-use and is lost silently > > as explained above, inaccurate either offset or free/in-use state of > a area is recorded into relevant chunk->map element if request a odd > alignment area, and so causes memory leakage issue > > fix it by forcing the @align of a area to allocate a even number > as do for @size. > > BTW, macro ALIGN() within pcpu_fit_in_area() is replaced by roundup() too > due to back reason. in order to align a value @v up to @a boundary, macro > roundup(v, a) is more generic than ALIGN(x, a); the latter doesn't work > well when @a isn't a power of 2 value. for example, roundup(10, 6) == 12 > but ALIGN(10, 6) == 10, the former result is desired obviously > > Signed-off-by: zijun_hu Nacked-by: Tejun Heo This is a fix for an imaginary problem. The most we should do about odd alignment is triggering a WARN_ON. Thanks. -- tejun -- 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