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=-2.6 required=3.0 tests=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 E4AF3C4740A for ; Mon, 7 Oct 2019 08:16:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AE38F2084D for ; Mon, 7 Oct 2019 08:16:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570436186; bh=ZogvcTmWmDXNGJ6SA2eRf+iGwobYOKAqrTOWer/PT+o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=ywczbW4K6Ry1lnoXBdRR1NtzwxB2MkgL7rbMvnEfJOs99xr16R2NDiNUZugXHRsU4 9SxU0bwnZYujHuTPZpoyTT9M7GsfgTn7zk0v+eY4Hz/CI3UFWhooh8NnoVsTIao9V0 RD7eGDjA4b3Hg0ZKyELlE6k08KRP/RqRu/0snklY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727461AbfJGIQ0 (ORCPT ); Mon, 7 Oct 2019 04:16:26 -0400 Received: from mx2.suse.de ([195.135.220.15]:56004 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726889AbfJGIQZ (ORCPT ); Mon, 7 Oct 2019 04:16:25 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 1DC79AD45; Mon, 7 Oct 2019 08:16:23 +0000 (UTC) Date: Mon, 7 Oct 2019 10:16:21 +0200 From: Michal Hocko To: Qian Cai Cc: akpm@linux-foundation.org, tj@kernel.org, vdavydov.dev@gmail.com, hannes@cmpxchg.org, guro@fb.com, cl@linux.com, penberg@kernel.org, rientjes@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] mm/slub: fix a deadlock in show_slab_objects() Message-ID: <20191007081621.GE2381@dhcp22.suse.cz> References: <1570192309-10132-1-git-send-email-cai@lca.pw> <20191004125701.GJ9578@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191004125701.GJ9578@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 04-10-19 14:57:01, Michal Hocko wrote: > On Fri 04-10-19 08:31:49, Qian Cai wrote: > > Long time ago, there fixed a similar deadlock in show_slab_objects() > > [1]. However, it is apparently due to the commits like 01fb58bcba63 > > ("slab: remove synchronous synchronize_sched() from memcg cache > > deactivation path") and 03afc0e25f7f ("slab: get_online_mems for > > kmem_cache_{create,destroy,shrink}"), this kind of deadlock is back by > > just reading files in /sys/kernel/slab which will generate a lockdep > > splat below. > > > > Since the "mem_hotplug_lock" here is only to obtain a stable online node > > mask while racing with NUMA node hotplug, in the worst case, the results > > may me miscalculated while doing NUMA node hotplug, but they shall be > > corrected by later reads of the same files. > > I think it is important to mention that this doesn't expose the > show_slab_objects to use-after-free. There is only a single path that > might really race here and that is the slab hotplug notifier callback > __kmem_cache_shrink (via slab_mem_going_offline_callback) but that path > doesn't really destroy kmem_cache_node data structures. Andrew, please add this to the changelog so that we do not have to scratch heads again when looking into that code. Thanks! -- Michal Hocko SUSE Labs