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 X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2946EC43441 for ; Thu, 15 Nov 2018 22:47:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EB7DD2133D for ; Thu, 15 Nov 2018 22:47:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EB7DD2133D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389147AbeKPI5I (ORCPT ); Fri, 16 Nov 2018 03:57:08 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:44066 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725916AbeKPI5H (ORCPT ); Fri, 16 Nov 2018 03:57:07 -0500 Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 48273B6D; Thu, 15 Nov 2018 22:47:20 +0000 (UTC) Date: Thu, 15 Nov 2018 14:47:19 -0800 From: Andrew Morton To: Sasha Levin Cc: stable@vger.kernel.org, linux-kernel@vger.kernel.org, Jann Horn , Davidlohr Bueso , Oleg Nesterov , Christoph Lameter , Kemi Wang , Andy Lutomirski , Ingo Molnar , Linus Torvalds , linux-mm@kvack.org Subject: Re: [PATCH AUTOSEL 3.18 8/9] mm/vmstat.c: assert that vmstat_text is in sync with stat_items_size Message-Id: <20181115144719.d26dc7a2d47fade8d41a83d5@linux-foundation.org> In-Reply-To: <20181115223718.GB1706@sasha-vm> References: <20181113055252.79406-1-sashal@kernel.org> <20181113055252.79406-8-sashal@kernel.org> <20181115140810.e3292c83467544f6a1d82686@linux-foundation.org> <20181115223718.GB1706@sasha-vm> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 15 Nov 2018 17:37:18 -0500 Sasha Levin wrote: > On Thu, Nov 15, 2018 at 02:08:10PM -0800, Andrew Morton wrote: > >On Tue, 13 Nov 2018 00:52:51 -0500 Sasha Levin wrote: > > > >> From: Jann Horn > >> > >> [ Upstream commit f0ecf25a093fc0589f0a6bc4c1ea068bbb67d220 ] > >> > >> Having two gigantic arrays that must manually be kept in sync, including > >> ifdefs, isn't exactly robust. To make it easier to catch such issues in > >> the future, add a BUILD_BUG_ON(). > >> > >> ... > >> > >> --- a/mm/vmstat.c > >> +++ b/mm/vmstat.c > >> @@ -1189,6 +1189,8 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos) > >> stat_items_size += sizeof(struct vm_event_state); > >> #endif > >> > >> + BUILD_BUG_ON(stat_items_size != > >> + ARRAY_SIZE(vmstat_text) * sizeof(unsigned long)); > >> v = kmalloc(stat_items_size, GFP_KERNEL); > >> m->private = v; > >> if (!v) > > > >I don't think there's any way in which this can make a -stable kernel > >more stable! > > > > > >Generally, I consider -stable in every patch I merge, so for each patch > >which doesn't have cc:stable, that tag is missing for a reason. > > > >In other words, your criteria for -stable addition are different from > >mine. > > > >And I think your criteria differ from those described in > >Documentation/process/stable-kernel-rules.rst. > > > >So... what is your overall thinking on patch selection? > > Indeed, this doesn't fix anything. > > My concern is that in the future, we will pull a patch that will cause > the issue described here, and that issue will only be relevant on > stable. It is very hard to debug this, and I suspect that stable kernels > will still pass all their tests with flying colors. > > As an example, consider the case where commit 28e2c4bb99aa ("mm/vmstat.c: > fix outdated vmstat_text") is backported to a kernel that doesn't have > commit 7a9cdebdcc17 ("mm: get rid of vmacache_flush_all() entirely"). > > I also felt safe with this patch since it adds a single BUILD_BUG_ON() > which does nothing during runtime, so the chances it introduces anything > beyond a build regression seemed to be slim to none. Well OK. But my question was general and covers basically every autosel patch which originated in -mm.