From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f200.google.com (mail-pl1-f200.google.com [209.85.214.200]) by kanga.kvack.org (Postfix) with ESMTP id 479836B0610 for ; Thu, 15 Nov 2018 17:37:20 -0500 (EST) Received: by mail-pl1-f200.google.com with SMTP id 89so1928499ple.19 for ; Thu, 15 Nov 2018 14:37:20 -0800 (PST) Received: from mail.kernel.org (mail.kernel.org. [198.145.29.99]) by mx.google.com with ESMTPS id e15si25941358pgg.281.2018.11.15.14.37.19 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 15 Nov 2018 14:37:19 -0800 (PST) Date: Thu, 15 Nov 2018 17:37:18 -0500 From: Sasha Levin Subject: Re: [PATCH AUTOSEL 3.18 8/9] mm/vmstat.c: assert that vmstat_text is in sync with stat_items_size Message-ID: <20181115223718.GB1706@sasha-vm> References: <20181113055252.79406-1-sashal@kernel.org> <20181113055252.79406-8-sashal@kernel.org> <20181115140810.e3292c83467544f6a1d82686@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20181115140810.e3292c83467544f6a1d82686@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton 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 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. -- Thanks, Sasha