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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable 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 697FFECE58C for ; Fri, 11 Oct 2019 09:31:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4309E21D71 for ; Fri, 11 Oct 2019 09:31:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727476AbfJKJbY (ORCPT ); Fri, 11 Oct 2019 05:31:24 -0400 Received: from mx2.suse.de ([195.135.220.15]:58142 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726788AbfJKJbY (ORCPT ); Fri, 11 Oct 2019 05:31:24 -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 10706B37E; Fri, 11 Oct 2019 09:31:21 +0000 (UTC) Subject: Re: [PATCH RESEND] mm: memcg/slab: fix panic in __free_slab() caused by premature memcg pointer release To: Roman Gushchin , linux-mm@kvack.org, Andrew Morton Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, Karsten Graul , Shakeel Butt , Vladimir Davydov , David Rientjes , stable@vger.kernel.org References: <20191010160549.1584316-1-guro@fb.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; prefer-encrypt=mutual; keydata= mQINBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy 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5ZFJyfGsOiNUcMoO/17FO4EBxSDP3FDLllpuzlFD7SXkfJaMWYmXIlO0jLzdfwfcnDzBbPwO hBM8hvtsyq8lq8vJOxv6XD6xcTtj5Az8t2JjdUX6SF9hxJpwhBU0wrCoGDkWp4Bbv6jnF7zP Nzftr4l8RuJoywDIiJpdaNpSlXKpj/K6KrnyAI/joYc7 Message-ID: <6e853d43-adfa-ab65-094e-b4a871e52ca4@suse.cz> Date: Fri, 11 Oct 2019 11:31:17 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 MIME-Version: 1.0 In-Reply-To: <20191010160549.1584316-1-guro@fb.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I believe it's better to include To: Andrew directly to have the patch picked up? On 10/10/19 6:05 PM, Roman Gushchin wrote: > Karsten reported the following panic in __free_slab() happening on a s390x > machine: > > 349.361168¨ Unable to handle kernel pointer dereference in virtual kernel address space > 349.361210¨ Failing address: 0000000000000000 TEID: 0000000000000483 > 349.361223¨ Fault in home space mode while using kernel ASCE. > 349.361240¨ AS:00000000017d4007 R3:000000007fbd0007 S:000000007fbff000 P:000000000000003d > 349.361340¨ Oops: 0004 ilc:3 Ý#1¨ PREEMPT SMP > 349.361349¨ Modules linked in: tcp_diag inet_diag xt_tcpudp ip6t_rpfilter ip6t_REJECT \ > nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack ip6table_nat ip6table_mangle \ > ip6table_raw ip6table_security iptable_at nf_nat > 349.361436¨ CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.3.0-05872-g6133e3e4bada-dirty #14 > 349.361445¨ Hardware name: IBM 2964 NC9 702 (z/VM 6.4.0) > 349.361450¨ Krnl PSW : 0704d00180000000 00000000003cadb6 (__free_slab+0x686/0x6b0) > 349.361464¨ R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:1 PM:0 RI:0 EA:3 > 349.361470¨ Krnl GPRS: 00000000f3a32928 0000000000000000 000000007fbf5d00 000000000117c4b8 > 349.361475¨ 0000000000000000 000000009e3291c1 0000000000000000 0000000000000000 > 349.361481¨ 0000000000000003 0000000000000008 000000002b478b00 000003d080a97600 > 349.361481¨ 0000000000000003 0000000000000008 000000002b478b00 000003d080a97600 > 349.361486¨ 000000000117ba00 000003e000057db0 00000000003cabcc 000003e000057c78 > 349.361500¨ Krnl Code: 00000000003cada6: e310a1400004 lg %r1,320(%r10) > 349.361500¨ 00000000003cadac: c0e50046c286 brasl %r14,ca32b8 > 349.361500¨ #00000000003cadb2: a7f4fe36 brc 15,3caa1e > 349.361500¨ >00000000003cadb6: e32060800024 stg %r2,128(%r6) > 349.361500¨ 00000000003cadbc: a7f4fd9e brc 15,3ca8f8 > 349.361500¨ 00000000003cadc0: c0e50046790c brasl %r14,c99fd8 > 349.361500¨ 00000000003cadc6: a7f4fe2c brc 15,3caa > 349.361500¨ 00000000003cadc6: a7f4fe2c brc 15,3caa1e > 349.361500¨ 00000000003cadca: ecb1ffff00d9 aghik %r11,%r1,-1 > 349.361619¨ Call Trace: > 349.361627¨ (Ý<00000000003cabcc>¨ __free_slab+0x49c/0x6b0) > 349.361634¨ Ý<00000000001f5886>¨ rcu_core+0x5a6/0x7e0 > 349.361643¨ Ý<0000000000ca2dea>¨ __do_softirq+0xf2/0x5c0 > 349.361652¨ Ý<0000000000152644>¨ irq_exit+0x104/0x130 > 349.361659¨ Ý<000000000010d222>¨ do_IRQ+0x9a/0xf0 > 349.361667¨ Ý<0000000000ca2344>¨ ext_int_handler+0x130/0x134 > 349.361674¨ Ý<0000000000103648>¨ enabled_wait+0x58/0x128 > 349.361681¨ (Ý<0000000000103634>¨ enabled_wait+0x44/0x128) > 349.361688¨ Ý<0000000000103b00>¨ arch_cpu_idle+0x40/0x58 > 349.361695¨ Ý<0000000000ca0544>¨ default_idle_call+0x3c/0x68 > 349.361704¨ Ý<000000000018eaa4>¨ do_idle+0xec/0x1c0 > 349.361748¨ Ý<000000000018ee0e>¨ cpu_startup_entry+0x36/0x40 > 349.361756¨ Ý<000000000122df34>¨ arch_call_rest_init+0x5c/0x88 > 349.361761¨ Ý<0000000000000000>¨ 0x0 > 349.361765¨ INFO: lockdep is turned off. > 349.361769¨ Last Breaking-Event-Address: > 349.361774¨ Ý<00000000003ca8f4>¨ __free_slab+0x1c4/0x6b0 > 349.361781¨ Kernel panic - not syncing: Fatal exception in interrupt > > The kernel panics on an attempt to dereference the NULL memcg pointer. > When shutdown_cache() is called from the kmem_cache_destroy() context, > a memcg kmem_cache might have empty slab pages in a partial list, > which are still charged to the memory cgroup. These pages are released > by free_partial() at the beginning of shutdown_cache(): either > directly or by scheduling a RCU-delayed work (if the kmem_cache has > the SLAB_TYPESAFE_BY_RCU flag). The latter case is when the reported > panic can happen: memcg_unlink_cache() is called immediately after > shrinking partial lists, without waiting for scheduled RCU works. > It sets the kmem_cache->memcg_params.memcg pointer to NULL, > and the following attempt to dereference it by __free_slab() > from the RCU work context causes the panic. > > To fix the issue, let's postpone the release of the memcg pointer > to destroy_memcg_params(). It's called from a separate work context > by slab_caches_to_rcu_destroy_workfn(), which contains a full RCU > barrier. This guarantees that all scheduled page release RCU works > will complete before the memcg pointer will be zeroed. > > Big thanks for Karsten for the perfect report containing all necessary > information, his help with the analysis of the problem and testing > of the fix. > > Fixes: fb2f2b0adb98 ("mm: memcg/slab: reparent memcg kmem_caches on cgroup removal") > Reported-by: Karsten Graul > Tested-by: Karsten Graul > Signed-off-by: Roman Gushchin > Cc: Karsten Graul > Cc: Shakeel Butt > Cc: Vladimir Davydov > Cc: David Rientjes > Cc: stable@vger.kernel.org Acked-by: Vlastimil Babka > --- > mm/slab_common.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 0b94a37da531..8afa188f6e20 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -178,10 +178,13 @@ static int init_memcg_params(struct kmem_cache *s, > > static void destroy_memcg_params(struct kmem_cache *s) > { > - if (is_root_cache(s)) > + if (is_root_cache(s)) { > kvfree(rcu_access_pointer(s->memcg_params.memcg_caches)); > - else > + } else { > + mem_cgroup_put(s->memcg_params.memcg); > + WRITE_ONCE(s->memcg_params.memcg, NULL); > percpu_ref_exit(&s->memcg_params.refcnt); > + } > } > > static void free_memcg_params(struct rcu_head *rcu) > @@ -253,8 +256,6 @@ static void memcg_unlink_cache(struct kmem_cache *s) > } else { > list_del(&s->memcg_params.children_node); > list_del(&s->memcg_params.kmem_caches_node); > - mem_cgroup_put(s->memcg_params.memcg); > - WRITE_ONCE(s->memcg_params.memcg, NULL); > } > } > #else >