From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f49.google.com (mail-pa0-f49.google.com [209.85.220.49]) by kanga.kvack.org (Postfix) with ESMTP id 93FD66B0106 for ; Sun, 23 Feb 2014 23:49:10 -0500 (EST) Received: by mail-pa0-f49.google.com with SMTP id hz1so6005757pad.22 for ; Sun, 23 Feb 2014 20:49:10 -0800 (PST) Received: from lgeamrelo04.lge.com (lgeamrelo04.lge.com. [156.147.1.127]) by mx.google.com with ESMTP id sh5si15303829pbc.260.2014.02.23.20.49.08 for ; Sun, 23 Feb 2014 20:49:09 -0800 (PST) Date: Mon, 24 Feb 2014 13:49:18 +0900 From: Joonsoo Kim Subject: Re: [PATCH 9/9] slab: remove a useless lockdep annotation Message-ID: <20140224044918.GA14814@lge.com> References: <1392361043-22420-1-git-send-email-iamjoonsoo.kim@lge.com> <1392361043-22420-10-git-send-email-iamjoonsoo.kim@lge.com> <20140217061201.GA3468@lge.com> 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: Christoph Lameter Cc: Pekka Enberg , Andrew Morton , David Rientjes , Wanpeng Li , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue, Feb 18, 2014 at 10:21:10AM -0600, Christoph Lameter wrote: > On Mon, 17 Feb 2014, Joonsoo Kim wrote: > > > > Why change the BAD_ALIEN_MAGIC? > > > > Hello, Christoph. > > > > BAD_ALIEN_MAGIC is only checked by slab_set_lock_classes(). We remove this > > function in this patch, so returning BAD_ALIEN_MAGIC is useless. > > Its not useless. The point is if there is a pointer deref then we will see > this as a pointer value and know that it is realted to alien cache > processing. > > > And, in fact, BAD_ALIEN_MAGIC is already useless, because alloc_alien_cache() > > can't be called on !CONFIG_NUMA. This function is called if use_alien_caches > > is positive, but on !CONFIG_NUMA, use_alien_caches is always 0. So we don't > > have any chance to meet this BAD_ALIEN_MAGIC in runtime. > > Maybe it no longer serves a point. But note that caches may not be > populated because processors/nodes are not up yet. Hello, Let me clarify about alloc_alien_cache(). alloc_alien_cache() has two definitions, one for !CONFIG_NUMA, and the other for CONFIG_NUMA. BAD_ALIEN_MAGIC is only assigned on !CONFIG_NUMA definition. On CONFIG_NUMA, alloc_alien_cache() doesn't use BAD_ALIEN_MAGIC. So it is sufficient to consider just !CONFIG_NUMA case. As I mentioned before, this function isn't called if use_alien_caches is zero and use_alien_caches is always zero on !CONFIG_NUMA. Therefore we cannot see BAD_ALIEN_MAGIC on any configuration. I don't know why BAD_ALIEN_MAGIC is introduced, however, it no longer serves a point, so it is better to remove it. There are lots of code to check whether processor/nodes are up or not and these doesn't use BAD_ALIEN_MAGIC. Instead, it checks NULL on alien_cache of specific node. So removing BAD_ALIEN_MAGIC doesn't harm anything here. Thanks. -- 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