From nobody Sat Apr 18 15:46:03 2026 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 5F6F8C433EF for ; Wed, 13 Jul 2022 18:39:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236677AbiGMSjH (ORCPT ); Wed, 13 Jul 2022 14:39:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41020 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231986AbiGMSjF (ORCPT ); Wed, 13 Jul 2022 14:39:05 -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 05F661AF35 for ; Wed, 13 Jul 2022 11:39:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1657737543; 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: content-transfer-encoding:content-transfer-encoding; bh=w9ISA9tgFxM9CIk2iQzh4LVvlpFF6ft7yZ2ywOZt+mg=; b=HDMRoYa88OFmOX8FkcYkG5tt1bszCdrSSxvMUJzW+JHN1hc25DIX1Q0bLhcJXDMthrI3hE Xino+YZMjQP+lbXA5Y99CYIP1fgEZ+rSklWf75+UYLvtRLTNR3LuOI7uleSjrpGe9RPrgc /2yzV3WCS+1gJqYbYmqsVoi3GwelC1o= 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-267-Nq5ZVIjBM5KxOSlR5OFdhg-1; Wed, 13 Jul 2022 14:38:57 -0400 X-MC-Unique: Nq5ZVIjBM5KxOSlR5OFdhg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4A6B9185A794; Wed, 13 Jul 2022 18:38:57 +0000 (UTC) Received: from pauld.bos.com (dhcp-17-237.bos.redhat.com [10.18.17.237]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0485318EBB; Wed, 13 Jul 2022 18:38:56 +0000 (UTC) From: Phil Auld To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , "Rafael J . Wysocki" , Barry Song <21cnbao@gmail.com>, Tian Tao Subject: [PATCH v3] drivers/base/node.c: fix userspace break from using bin_attributes for cpumap and cpulist Date: Wed, 13 Jul 2022 14:38:55 -0400 Message-Id: <20220713183855.2188201-1-pauld@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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 brea= k the size limitation of cpumap ABI") let's put in a size value at compile time. Use d= irect comparison and a worst-case maximum to ensure compile time constants. For c= pulist 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 m= ath and support larger NR_CPUS we are using NR_CPUS * 7 to support a future with mu= ch larger NR_CPUS. We also set it to a min of PAGE_SIZE to retain the older behavior for small= er 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 =3D=3D 8192) before: -r--r--r--. 1 root root 0 Jul 12 14:08 /sys/devices/system/node/node0/cpuli= st -r--r--r--. 1 root root 0 Jul 11 17:25 /sys/devices/system/node/node0/cpumap after: -r--r--r--. 1 root root 57344 Jul 13 11:32 /sys/devices/system/node/node0/c= pulist -r--r--r--. 1 root root 4096 Jul 13 11:31 /sys/devices/system/node/node0/c= pumap NR_CPUS =3D 16384 -r--r--r--. 1 root root 114688 Jul 13 14:03 /sys/devices/system/node/node0/= cpulist -r--r--r--. 1 root root 8192 Jul 13 14:02 /sys/devices/system/node/node0/= cpumap Fixes: 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the si= ze limitation of cpumap ABI") Cc: Greg Kroah-Hartman Cc: "Rafael J. Wysocki" Signed-off-by: Phil Auld --- drivers/base/node.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/drivers/base/node.c b/drivers/base/node.c index 0ac6376ef7a1..89c932a1d8ca 100644 --- a/drivers/base/node.c +++ b/drivers/base/node.c @@ -45,7 +45,11 @@ static inline ssize_t cpumap_read(struct file *file, str= uct kobject *kobj, return n; } =20 -static BIN_ATTR_RO(cpumap, 0); +/* Report a valid max size for this file to avoid breaking userspace. We u= se NR_CPUS/2 as=20 + * a simplification of NR_CPUS/8 + NR_CPUS/32. Use PAGE_SIZE as a minimum= for smaller=20 + * configurations.=20 + */=20 +static BIN_ATTR_RO(cpumap, (((NR_CPUS >> 1) > PAGE_SIZE) ? NR_CPUS >> 1 : = PAGE_SIZE)); =20 static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj, struct bin_attribute *attr, char *buf, @@ -66,7 +70,15 @@ static inline ssize_t cpulist_read(struct file *file, st= ruct kobject *kobj, return n; } =20 -static BIN_ATTR_RO(cpulist, 0); +/* Report a valid maximum size for this file since 0 breaks userspace, whi= ch + * may use the size from fstat to allocate a read buffer.=20 + * The value 7 is a hardcoded version of ceil(log10(NR_CPUS)) + 1 for futu= re values + * of NR_CPUS that may be upto 2 orders of magnitude larger than 8192. + * In a worst case system every other cpu is on one of two nodes. This lea= ds to=20 + * a file like "0,2,4,6,8...1024,...8190,...". Use PAGE_SIZE as a minimum = for smaller + * NR_CPUS. =20 +*/ +static BIN_ATTR_RO(cpulist, (((NR_CPUS * 7) > PAGE_SIZE) ? NR_CPUS * 7 : P= AGE_SIZE)); =20 /** * struct node_access_nodes - Access class device to hold user visible --=20 2.31.1