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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 F1C98C433E9 for ; Mon, 15 Mar 2021 17:37:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A4F5E64E04 for ; Mon, 15 Mar 2021 17:37:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234502AbhCORhO (ORCPT ); Mon, 15 Mar 2021 13:37:14 -0400 Received: from mx2.suse.de ([195.135.220.15]:53154 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236285AbhCORgj (ORCPT ); Mon, 15 Mar 2021 13:36:39 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 35D55AE8F; Mon, 15 Mar 2021 17:36:38 +0000 (UTC) Subject: Re: [PATCH] [PATCH] mm, slub: enable slub_debug static key when creating cache with explicit debug flags To: paulmck@kernel.org Cc: David Rientjes , Andrew Morton , Christoph Lameter , Pekka Enberg , Joonsoo Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org, David Sterba , Oliver Glitta References: <20210315153415.24404-1-vbabka@suse.cz> <2d80f81a-ed85-a36f-6527-b75da3ae209e@google.com> <20210315173207.GN2696@paulmck-ThinkPad-P72> From: Vlastimil Babka Message-ID: <8c4f3385-e935-8363-c6bd-ffe6b8c2d6c4@suse.cz> Date: Mon, 15 Mar 2021 18:36:34 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210315173207.GN2696@paulmck-ThinkPad-P72> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/15/21 6:32 PM, Paul E. McKenney wrote: > On Mon, Mar 15, 2021 at 06:28:42PM +0100, Vlastimil Babka wrote: >> On 3/15/21 6:16 PM, David Rientjes wrote: >> > On Mon, 15 Mar 2021, Vlastimil Babka wrote: >> > >> >> Commit ca0cab65ea2b ("mm, slub: introduce static key for slub_debug()") >> >> introduced a static key to optimize the case where no debugging is enabled for >> >> any cache. The static key is enabled when slub_debug boot parameter is passed, >> >> or CONFIG_SLUB_DEBUG_ON enabled. >> >> >> >> However, some caches might be created with one or more debugging flags >> >> explicitly passed to kmem_cache_create(), and the commit missed this. Thus the >> >> debugging functionality would not be actually performed for these caches unless >> >> the static key gets enabled by boot param or config. >> >> >> >> This patch fixes it by checking for debugging flags passed to >> >> kmem_cache_create() and enabling the static key accordingly. >> >> >> >> Note such explicit debugging flags should not be used outside of debugging and >> >> testing as they will now enable the static key globally. btrfs_init_cachep() >> >> creates a cache with SLAB_RED_ZONE but that's a mistake that's being corrected >> >> [1]. rcu_torture_stats() creates a cache with SLAB_STORE_USER, but that is a >> >> testing module so it's OK and will start working as intended after this patch. >> >> >> >> Also note that in case of backports to kernels before v5.12 that don't have >> >> 59450bbc12be ("mm, slab, slub: stop taking cpu hotplug lock"), >> >> static_branch_enable_cpuslocked() should be used. >> >> >> > >> > Since this affects 5.9+, is the plan to propose backports to stable with >> > static_branch_enable_cpuslocked() once this is merged? (I notice the >> > absence of the stable tag here, which I believe is intended.) >> >> I was thinking about it, and since the rcutorture user is only in -next (AFAICS) >> and btrfs user was unintended, it didn't seem to meet stable criteria to me. But >> I won't mind if it's backported. > > I had better ask... Should rcutorture be doing something different? > > Thanx, Paul No, I think it's fine if a testing module such as rcutorture flips the static key for the rest of the kernel's uptime. I only CC'd you as FYI in case you were wondering why you can't see any alloc/free stacks in its output :)