From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f198.google.com (mail-pg1-f198.google.com [209.85.215.198]) by kanga.kvack.org (Postfix) with ESMTP id 9EEE26B0649 for ; Thu, 15 Nov 2018 18:01:20 -0500 (EST) Received: by mail-pg1-f198.google.com with SMTP id 143so11381914pgc.3 for ; Thu, 15 Nov 2018 15:01:20 -0800 (PST) Received: from mail.kernel.org (mail.kernel.org. [198.145.29.99]) by mx.google.com with ESMTPS id x11-v6si29096584pln.425.2018.11.15.15.01.19 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 15 Nov 2018 15:01:19 -0800 (PST) Date: Thu, 15 Nov 2018 18:01:18 -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: <20181115230118.GC1706@sasha-vm> References: <20181113055252.79406-1-sashal@kernel.org> <20181113055252.79406-8-sashal@kernel.org> <20181115140810.e3292c83467544f6a1d82686@linux-foundation.org> <20181115223718.GB1706@sasha-vm> <20181115144719.d26dc7a2d47fade8d41a83d5@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20181115144719.d26dc7a2d47fade8d41a83d5@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 02:47:19PM -0800, Andrew Morton wrote: >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. Sure. I picked 3 patches that show up on top when I google for AUTOSEL in linux-mm, maybe they'll be a good example to help me understand why they were not selected. This one fixes a case where too few struct pages are allocated when using mirrorred memory: https://marc.info/?l=linux-mm&m=154211933211147&w=2 Race condition with memory hotplug due to missing locks: https://marc.info/?l=linux-mm&m=154211934011188&w=2 Raising an OOM event that causes issues in userspace when no OOM has actually occured: https://marc.info/?l=linux-mm&m=154211939811582&w=2 I think that all 3 cases represent a "real" bug users can hit, and I honestly don't know why they were not tagged for stable. -- Thanks, Sasha