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 76A32C433EF for ; Wed, 13 Jul 2022 11:48:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236236AbiGMLsH (ORCPT ); Wed, 13 Jul 2022 07:48:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40016 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235683AbiGMLsF (ORCPT ); Wed, 13 Jul 2022 07:48:05 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 991DF1034C4 for ; Wed, 13 Jul 2022 04:48:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1657712883; 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=5Mww04r+3ec6OV9BE9n56mJoBDx1peSx+B2QTleOL7s=; b=Fa13forx9hWeZtr9KxNrfqt+ACh87X9bFMF8CTmJ7D6Yo/8SrNRMGDShClYQt6g0bizvbG oKHxXQ4cOnfuHKL41WnJGF0/BvDtklazQJalxTtpAUwDUzPV9L0fOme0fFp0EtCRSdIrv+ GmqAHeirrBxPZdc9ipuYVBqgcijj67s= 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-460-cxwzfLWZOEC8mISIsEiD4g-1; Wed, 13 Jul 2022 07:48:00 -0400 X-MC-Unique: cxwzfLWZOEC8mISIsEiD4g-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 2C7798032F6; Wed, 13 Jul 2022 11:48:00 +0000 (UTC) Received: from lorien.usersys.redhat.com (unknown [10.22.32.177]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D81D4492C3B; Wed, 13 Jul 2022 11:47:59 +0000 (UTC) Date: Wed, 13 Jul 2022 07:47:58 -0400 From: Phil Auld To: Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, "Rafael J . Wysocki" , 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: X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Greg, On Wed, Jul 13, 2022 at 08:06:02AM +0200 Greg Kroah-Hartman wrote: > On Tue, Jul 12, 2022 at 05:43:01PM -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. > > 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. > > Does userspace care about that size, or can we just put any value in > there and it will be ok? How about just returning to the original > PAGE_SIZE value to keep things looking identical, will userspace not > read more than that size from the file then? > I'll go look. But I think the point of pre-reading the size with fstat is to allocate a buffer to read into. So that may be a problem. That said, I believe in this case it's the cpulist file which given the use of ranges is very unlikely to actually get that big. > > On an 80 cpu 4-node sytem (NR_CPUS == 8192) > > We have systems running Linux with many more cpus than that, and your > company knows this :) The 80 cpus here don't matter and we only build with NR_CPUS = 8192 :) But yes, I realize now that the cpumap part I posted is broken for larger NR_CPUS. I originally had it as NR_CPUS, but as I said in my reply to Barry, it wants to be ~= NR_CPUS/4 + NR_CPUS/32. I'll change that. I think we should decide on a max for each and use that. Cheers, Phil > > thanks, > > greg k-h > --