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=-2.5 required=3.0 tests=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 6AFFFECE58D for ; Mon, 7 Oct 2019 08:16:27 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 360A92084D for ; Mon, 7 Oct 2019 08:16:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 360A92084D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id CE09C8E0005; Mon, 7 Oct 2019 04:16:26 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C91E88E0003; Mon, 7 Oct 2019 04:16:26 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BA7898E0005; Mon, 7 Oct 2019 04:16:26 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0052.hostedemail.com [216.40.44.52]) by kanga.kvack.org (Postfix) with ESMTP id 987508E0003 for ; Mon, 7 Oct 2019 04:16:26 -0400 (EDT) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id 4410E482A for ; Mon, 7 Oct 2019 08:16:26 +0000 (UTC) X-FDA: 76016281572.15.horn73_1b0f5704f6654 X-HE-Tag: horn73_1b0f5704f6654 X-Filterd-Recvd-Size: 2473 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf10.hostedemail.com (Postfix) with ESMTP for ; Mon, 7 Oct 2019 08:16:25 +0000 (UTC) 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) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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