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 C1DB4C433EF for ; Wed, 13 Jul 2022 13:58:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236306AbiGMN6y (ORCPT ); Wed, 13 Jul 2022 09:58:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33462 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235802AbiGMN6t (ORCPT ); Wed, 13 Jul 2022 09:58:49 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2F32E65A7 for ; Wed, 13 Jul 2022 06:58:48 -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 dfw.source.kernel.org (Postfix) with ESMTPS id C719C61D92 for ; Wed, 13 Jul 2022 13:58:47 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7990FC34114; Wed, 13 Jul 2022 13:58:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1657720727; bh=e/BMPIIZAaUiscbT6bTx/taPR68QeZbo8DuWen9ljuM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=k7Q6w5Z2xcPNbwK+yx78wDiJF9mqEX1xEY9D3vA9RaQ7OjyoD0hkY07zXZkv6ZNPS L1+bHp5Rdv0VuwdEBeeitO8h8GlpQvbS0FV0OuKDhSziuNfSnw8OniteOoqYeV0vdV j1a1u64fBSgCE6LvIcH9QmoilP/loRpuk9XaXYfg= Date: Wed, 13 Jul 2022 15:58:43 +0200 From: Greg Kroah-Hartman To: Phil Auld Cc: linux-kernel@vger.kernel.org, "Rafael J . Wysocki" , Barry Song <21cnbao@gmail.com>, Tian Tao Subject: Re: [PATCH v2] drivers/base/node.c: fix userspace break from using bin_attributes for cpumap and cpulist Message-ID: References: <20220713134545.1382367-1-pauld@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220713134545.1382367-1-pauld@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 13, 2022 at 09:45:45AM -0400, 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 > (8192 * 5). 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...). To simplify the math and > support larger NR_CPUS we are using NR_CPUS * 6. We also set it to a min of PAGE_SIZE > to retain the older behavior for smaller NR_CPUS. The cpumap file wants to be something > like NR_CPUS/4 + NR_CPUS/32, for the ","s so for simplicity we are using NR_CPUS/2. > > On an 80 cpu 4-node sytem (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 > > after: > > -r--r--r--. 1 root root 49152 Jul 13 09:26 /sys/devices/system/node/node0/cpulist > -r--r--r--. 1 root root 4096 Jul 13 09:24 /sys/devices/system/node/node0/cpumap > > Fixes: 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI") > Cc: Greg Kroah-Hartman > Cc: "Rafael J. Wysocki" > Signed-off-by: Phil Auld > --- > drivers/base/node.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/base/node.c b/drivers/base/node.c > index 0ac6376ef7a1..3577f4eb4ac6 100644 > --- a/drivers/base/node.c > +++ b/drivers/base/node.c > @@ -45,7 +45,7 @@ static inline ssize_t cpumap_read(struct file *file, struct kobject *kobj, > return n; > } > > -static BIN_ATTR_RO(cpumap, 0); > +static BIN_ATTR_RO(cpumap, (((NR_CPUS>>1) > PAGE_SIZE) ? NR_CPUS >> 1 : PAGE_SIZE)); Why not just PAGE_SIZE? If not, a HUGE comment explaining what you are doing here is going to be required. > > static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj, > struct bin_attribute *attr, char *buf, > @@ -66,7 +66,7 @@ static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj, > return n; > } > > -static BIN_ATTR_RO(cpulist, 0); > +static BIN_ATTR_RO(cpulist, (((NR_CPUS * 6) > PAGE_SIZE) ? NR_CPUS *6 : PAGE_SIZE)); "* 6" in both places here? And again, we need a huge comment explaining this so that we can understand it in a few weeks, and in 10 years... thanks, greg k-h