From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753280Ab2A3SQp (ORCPT ); Mon, 30 Jan 2012 13:16:45 -0500 Received: from mail-iy0-f174.google.com ([209.85.210.174]:47923 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752246Ab2A3SQo (ORCPT ); Mon, 30 Jan 2012 13:16:44 -0500 Date: Mon, 30 Jan 2012 10:16:39 -0800 From: Tejun Heo To: Christoph Lameter Cc: Dmitry Antipov , Rusty Russell , linux-mm@kvack.org, linux-kernel@vger.kernel.org, patches@linaro.org, linaro-dev@lists.linaro.org Subject: Re: [PATCH 1/3] percpu: use ZERO_SIZE_PTR / ZERO_OR_NULL_PTR Message-ID: <20120130181639.GJ3355@google.com> References: <1327912654-8738-1-git-send-email-dmitry.antipov@linaro.org> <20120130171558.GB3355@google.com> <20120130174256.GF3355@google.com> <20120130175434.GG3355@google.com> <20120130180224.GH3355@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 30, 2012 at 12:12:18PM -0600, Christoph Lameter wrote: > > I thought it didn't. I rememer thinking about this and determining > > that NULL can't be allocated for dynamic addresses. Maybe I'm > > imagining things. Anyways, if it can return NULL for valid > > allocation, it is a bug and should be fixed. > > I dont see anything that would hinder an arbitrary value to be returned. > NULL is also used for the failure case. Definitely a bug. Given the address translation we do and kernel image layout, I don't think this can happen on x86. It may theoretically possible on other archs tho. Anyways, yeah, this one needs improving. > > We don't have returned addr >= PAGE_SIZE guarantee yet but I'm fairly > > sure that's the only acceptable direction if we want any improvement > > in this area. > > The ZERO_SIZE_PTR patch would not make the situation that much worse. I'm not objecting to marking zero-sized allocations per-se. I'm saying the patch is pointless at this point. It doesn't contribute anything while giving the illusion of better error checking than we actually do. Let's do it when it can actually work. Thanks. -- tejun