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 B45ACC43334 for ; Wed, 13 Jul 2022 14:25:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234656AbiGMOZk (ORCPT ); Wed, 13 Jul 2022 10:25:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59522 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229497AbiGMOZf (ORCPT ); Wed, 13 Jul 2022 10:25:35 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 05F4730572 for ; Wed, 13 Jul 2022 07:25:35 -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 99BD761DCD for ; Wed, 13 Jul 2022 14:25:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 63EB6C34114; Wed, 13 Jul 2022 14:25:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1657722334; bh=GqcKhLMme2XRMten/jm7ZOrt21JXJHyJD21A4eNiL7g=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=keEgJhqaweRJnjFlZaWt/kdMX9uj0iaMueByIac72DC7Hpzk/0n1LXJf40FSr6THR 0ROaeFqhWLAVK2RI/8J3JEPgL9XrDcDRlvEQa7uwNHO0nGPEoQq1bNvLDcwCTpjZAk C+aOUWi1G+i3caxugd+mvXLGQILWxcmIJLyWinQ0= Date: Wed, 13 Jul 2022 16:25:30 +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: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 13, 2022 at 10:13:28AM -0400, Phil Auld wrote: > 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. One order for now that we know of, probably larger that we don't :) > > > 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. Sorry, I was trying to point out to use a " " before the "6" in both places. Not questioning the math. thanks, greg k-h