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 EB085C433EF for ; Wed, 13 Jul 2022 13:06:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235711AbiGMNGC (ORCPT ); Wed, 13 Jul 2022 09:06:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54116 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229640AbiGMNGA (ORCPT ); Wed, 13 Jul 2022 09:06:00 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AF6328F for ; Wed, 13 Jul 2022 06:05:58 -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 ams.source.kernel.org (Postfix) with ESMTPS id 70C62B81F01 for ; Wed, 13 Jul 2022 13:05:57 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8710DC34114; Wed, 13 Jul 2022 13:05:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1657717556; bh=EAXJgBwI2keLSIZeMjBVYhrmB+hmvho7oKlJJvuBDX0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=SZOes/DyH4JRiebZpMxx53KG38Dafheux35ejHA0o9MHMZpakEvwj43twiQyl3abP UfeF4rbCTbQs2ydHXAQlZ9+437+WVwPYu8oRqJ78uyNKiT/Awonlt/OKmF8nAExojw dfoAblEzeIZ1gcslNHonoE2yKR5aR306u0rjxKDg= Date: Wed, 13 Jul 2022 15:05:52 +0200 From: Greg Kroah-Hartman To: Phil Auld 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: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 13, 2022 at 07:47:58AM -0400, Phil Auld wrote: > 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. That is why we had to change this to a binary file. Think about every-other CPU being there, that's a huge list. This already was broken on some systems which is why it had to be changed (i.e. we didn't change it for no reason at all.) > > > 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. Sure, pick a max size please, that's fine with me. greg k-h