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 33D5AC4CED1 for ; Fri, 4 Oct 2019 12:57:05 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0B3AD222C7 for ; Fri, 4 Oct 2019 12:57:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0B3AD222C7 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 9C2F56B0005; Fri, 4 Oct 2019 08:57:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 972B56B0007; Fri, 4 Oct 2019 08:57:04 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 862726B0008; Fri, 4 Oct 2019 08:57:04 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0095.hostedemail.com [216.40.44.95]) by kanga.kvack.org (Postfix) with ESMTP id 61EF96B0005 for ; Fri, 4 Oct 2019 08:57:04 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id 03810180AD7C3 for ; Fri, 4 Oct 2019 12:57:04 +0000 (UTC) X-FDA: 76006102368.28.size68_77dc7fc077315 X-HE-Tag: size68_77dc7fc077315 X-Filterd-Recvd-Size: 2235 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf22.hostedemail.com (Postfix) with ESMTP for ; Fri, 4 Oct 2019 12:57:03 +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 6794DB123; Fri, 4 Oct 2019 12:57:02 +0000 (UTC) Date: Fri, 4 Oct 2019 14:57:01 +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: <20191004125701.GJ9578@dhcp22.suse.cz> References: <1570192309-10132-1-git-send-email-cai@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1570192309-10132-1-git-send-email-cai@lca.pw> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, 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 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. Thanks! -- Michal Hocko SUSE Labs