From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5F95AC433EF for ; Wed, 13 Jul 2022 13:06:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235726AbiGMNGd (ORCPT ); Wed, 13 Jul 2022 09:06:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54648 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229640AbiGMNGc (ORCPT ); Wed, 13 Jul 2022 09:06:32 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C5CFB8F for ; Wed, 13 Jul 2022 06:06:31 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 708E5B81F01 for ; Wed, 13 Jul 2022 13:06:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9A73EC34114; Wed, 13 Jul 2022 13:06:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1657717589; bh=I/8fgDiVhnQn+g4npPm+EFV2apCMQYq4lmg3gRkrX5A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=RCnnZ5qfDQxP81MKBUlOpjlcR8nVBAkxZYruHpAfkjACJXmeHrCjG7/7ak8I7mERB bClPoF99tHTeV+XmL8u9WAZzgVRdlp5dACgY1ZDgjX1rZZm2BC4HFILR7vhRFnS1mI AFC+ubeNtWL7LXuMWpsVCX6tKTSm7h0x7/9eIqAg= Date: Wed, 13 Jul 2022 15:06:25 +0200 From: Greg Kroah-Hartman To: Phil Auld Cc: Barry Song <21cnbao@gmail.com>, LKML , "Rafael J . Wysocki : --cc=" , Tian Tao , Barry Song Subject: Re: [PATCH] drivers/base/node.c: fix userspace break from using bin_attributes for cpumap and cpulist Message-ID: References: <20220712214301.809967-1-pauld@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 13, 2022 at 07:37:27AM -0400, Phil Auld wrote: > On Wed, Jul 13, 2022 at 11:18:59AM +1200 Barry Song wrote: > > On Wed, Jul 13, 2022 at 9:58 AM Phil Auld wrote: > > > > > > Using bin_attributes with a 0 size causes fstat and friends to return that 0 size. > > > This breaks userspace code that retrieves the size before reading the file. Rather > > > than reverting 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size > > > limitation of cpumap ABI") let's put in a size value at compile time. Use direct > > > comparison and a worst-case maximum to ensure compile time constants. For cpulist the > > > max is on the order of NR_CPUS * (ceil(log10(NR_CPUS)) + 1) which for 8192 is 40960. > > > In order to get near that you'd need a system with every other CPU on one node or > > > something similar. e.g. (0,2,4,... 1024,1026...). We set it to a min of PAGE_SIZE > > > to retain the older behavior. For cpumap, PAGE_SIZE is plenty big. > > > > > > On an 80 cpu 4-node system (NR_CPUS == 8192) > > > > > > before: > > > > > > -r--r--r--. 1 root root 0 Jul 12 14:08 /sys/devices/system/node/node0/cpulist > > > -r--r--r--. 1 root root 0 Jul 11 17:25 /sys/devices/system/node/node0/cpumap > > > > it is a fundamental problem of bin_attr, isn't it? when we don't know the > > exact size of an attribute, and this size might become more than one > > PAGE_SIZE, we use bin_attr to break the limitation. but the fact is that > > we really don't know or it is really hard to know the actual size of the > > attribute. > > > > But it broke userspace applications. I figured rather than revert it maybe > we can find a max size to put in there and make it continue to work. Yes, we need to do this, we can't break userspace. thanks, greg k-h