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 EE90CC433EF for ; Wed, 13 Jul 2022 14:13:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235794AbiGMONn (ORCPT ); Wed, 13 Jul 2022 10:13:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47898 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229770AbiGMONh (ORCPT ); Wed, 13 Jul 2022 10:13:37 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 9CDAA2AC3 for ; Wed, 13 Jul 2022 07:13:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1657721615; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=16fe0zG+Df80Kw/yiUxFcqE0wkKzreKjMLbVHAylSVs=; b=XEIAvEbqe2WmnngYIdejpMstSw2gdIPnN6YBImU/w/+n2aIFILogFSLBSSTcBsHx/Zl7wO Vyw58IonxRGrkbW4ZrbX7p9cTC1BxcyOtEHNHjCRed/hQerUiZaMv40GrMbCDvL+ZO/kxy kHlXze8WNY6mbt/W/847gO81YN2HF8E= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-271-2JqrfoevOESecsRjA0hvJQ-1; Wed, 13 Jul 2022 10:13:31 -0400 X-MC-Unique: 2JqrfoevOESecsRjA0hvJQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id CF853811E76; Wed, 13 Jul 2022 14:13:30 +0000 (UTC) Received: from lorien.usersys.redhat.com (unknown [10.22.32.177]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 146842026D64; Wed, 13 Jul 2022 14:13:30 +0000 (UTC) Date: Wed, 13 Jul 2022 10:13:28 -0400 From: Phil Auld To: Greg Kroah-Hartman 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: X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 13, 2022 at 03:58:43PM +0200 Greg Kroah-Hartman wrote: > 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? > This one is likely to grow beyond page size if NR_CPUS is larger than 8192. It's about 2300 bytes at 8192 if my math is right. Let me ask again before I write the comments... what values of NR_CPUS are you seeing? Are people using an order of magnitude above 8192? Two orders? This patch (with the 6 below) handles about 1 order more. > If not, a HUGE comment explaining what you are doing here is going to be > required. Sure, will do. See above :) > > > > > 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? > It's compile time so it's cheap. But yes, 6 in both places. That's to support NR_CPUS=100000. > And again, we need a huge comment explaining this so that we can > understand it in a few weeks, and in 10 years... Will do. Thanks, Phil > > thanks, > > greg k-h > --