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=-7.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,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 43CE6C433DB for ; Mon, 15 Mar 2021 18:00:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1726164F2B for ; Mon, 15 Mar 2021 18:00:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230064AbhCOR7r (ORCPT ); Mon, 15 Mar 2021 13:59:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:46290 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230051AbhCOR7c (ORCPT ); Mon, 15 Mar 2021 13:59:32 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 4927964E81; Mon, 15 Mar 2021 17:59:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1615831172; bh=PywP2e9DwoaZXH2HBFQoUUv4R4W/QxpkPTvLkp6GMu4=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=ITTzXPnUEF8zbxUyFT4KyU/OzafCEUcYs/sobN0oCmoaar4jwu9t4fkA7zl1JU4MU zKGYNPGONHR+Sl+jFvgKWdSBSSPNzhR8+AzLQ6T7ttoovA92vlspF10uyxmMIjLHPz mwfYuqS2PggzithN33efTxX7ZZWRB3vPHvwkbPvJRtkdhe6cwLtAKW8ZMK+uGdepTS HfGgHO0XHT7UpWo+sNHS/dThtcMKXJluR6us/PMAEfn6hjkA58JumTmxhfXVznDLPs k1nojHN+D0q8ikYrUq7dptPUkkXVtaMFVGjI6LNSB1XRnQX9tXsV3YNS3C8ki1jPop 9ZQsbNiFUFOsQ== Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 0CECB352261C; Mon, 15 Mar 2021 10:59:32 -0700 (PDT) Date: Mon, 15 Mar 2021 10:59:32 -0700 From: "Paul E. McKenney" To: Vlastimil Babka 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 Subject: Re: [PATCH] [PATCH] mm, slub: enable slub_debug static key when creating cache with explicit debug flags Message-ID: <20210315175932.GO2696@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20210315153415.24404-1-vbabka@suse.cz> <2d80f81a-ed85-a36f-6527-b75da3ae209e@google.com> <20210315173207.GN2696@paulmck-ThinkPad-P72> <8c4f3385-e935-8363-c6bd-ffe6b8c2d6c4@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8c4f3385-e935-8363-c6bd-ffe6b8c2d6c4@suse.cz> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Mon, Mar 15, 2021 at 06:36:34PM +0100, Vlastimil Babka wrote: > 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 :) Ah, all of my recent tests have been for sufficient duration that all was well by the time that that code was invoked. But thank you for the heads up -- someone will hit this sooner or later, and I freely confess that I would have been clueless. Thanx, Paul