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=-11.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, 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 3DE41C433E0 for ; Wed, 15 Jul 2020 11:32:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 238592063A for ; Wed, 15 Jul 2020 11:32:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728873AbgGOLcD (ORCPT ); Wed, 15 Jul 2020 07:32:03 -0400 Received: from [195.135.220.15] ([195.135.220.15]:41842 "EHLO mx2.suse.de" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1726212AbgGOLcD (ORCPT ); Wed, 15 Jul 2020 07:32:03 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id BA70BB5A3; Wed, 15 Jul 2020 11:32:04 +0000 (UTC) Subject: Re: [PATCH v5.4.y, v4.19.y] mm: memcg/slab: fix memory leak at non-root kmem_cache destroy To: Muchun Song , cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, shakeelb@google.com, Roman Gushchin References: <20200707062754.8383-1-songmuchun@bytedance.com> From: Vlastimil Babka Message-ID: <3d06418e-e75c-e7b8-91cd-ba56283045be@suse.cz> Date: Wed, 15 Jul 2020 13:32:00 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200707062754.8383-1-songmuchun@bytedance.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/7/20 8:27 AM, Muchun Song wrote: > If the kmem_cache refcount is greater than one, we should not > mark the root kmem_cache as dying. If we mark the root kmem_cache > dying incorrectly, the non-root kmem_cache can never be destroyed. > It resulted in memory leak when memcg was destroyed. We can use the > following steps to reproduce. > > 1) Use kmem_cache_create() to create a new kmem_cache named A. > 2) Coincidentally, the kmem_cache A is an alias for kmem_cache B, > so the refcount of B is just increased. > 3) Use kmem_cache_destroy() to destroy the kmem_cache A, just > decrease the B's refcount but mark the B as dying. > 4) Create a new memory cgroup and alloc memory from the kmem_cache > A. It leads to create a non-root kmem_cache for allocating. > 5) When destroy the memory cgroup created in the step 4), the > non-root kmem_cache can never be destroyed. > > If we repeat steps 4) and 5), this will cause a lot of memory leak. > So only when refcount reach zero, we mark the root kmem_cache as dying. > > Fixes: 92ee383f6daa ("mm: fix race between kmem_cache destroy, create and deactivate") > Signed-off-by: Muchun Song CC Roman, who worked in this area recently. Also why is this marked "[PATCH v5.4.y, v4.19.y]"? Has it been fixed otherwise in 5.5+ ? > --- > mm/slab_common.c | 43 +++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 41 insertions(+), 2 deletions(-) > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 8c1ffbf7de45..83ee6211aec7 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -258,6 +258,11 @@ static void memcg_unlink_cache(struct kmem_cache *s) > list_del(&s->memcg_params.kmem_caches_node); > } > } > + > +static inline bool memcg_kmem_cache_dying(struct kmem_cache *s) > +{ > + return is_root_cache(s) && s->memcg_params.dying; > +} > #else > static inline int init_memcg_params(struct kmem_cache *s, > struct kmem_cache *root_cache) > @@ -272,6 +277,11 @@ static inline void destroy_memcg_params(struct kmem_cache *s) > static inline void memcg_unlink_cache(struct kmem_cache *s) > { > } > + > +static inline bool memcg_kmem_cache_dying(struct kmem_cache *s) > +{ > + return false; > +} > #endif /* CONFIG_MEMCG_KMEM */ > > /* > @@ -326,6 +336,13 @@ int slab_unmergeable(struct kmem_cache *s) > if (s->refcount < 0) > return 1; > > + /* > + * If the kmem_cache is dying. We should also skip this > + * kmem_cache. > + */ > + if (memcg_kmem_cache_dying(s)) > + return 1; > + > return 0; > } > > @@ -944,8 +961,6 @@ void kmem_cache_destroy(struct kmem_cache *s) > if (unlikely(!s)) > return; > > - flush_memcg_workqueue(s); > - > get_online_cpus(); > get_online_mems(); > > @@ -955,6 +970,30 @@ void kmem_cache_destroy(struct kmem_cache *s) > if (s->refcount) > goto out_unlock; > > +#ifdef CONFIG_MEMCG_KMEM > + mutex_unlock(&slab_mutex); > + > + put_online_mems(); > + put_online_cpus(); > + > + flush_memcg_workqueue(s); > + > + get_online_cpus(); > + get_online_mems(); > + > + mutex_lock(&slab_mutex); > + > + if (WARN(s->refcount, > + "kmem_cache_destroy %s: Slab cache is still referenced\n", > + s->name)) { > + /* > + * Reset the dying flag setted by flush_memcg_workqueue(). > + */ > + s->memcg_params.dying = false; > + goto out_unlock; > + } > +#endif > + > err = shutdown_memcg_caches(s); > if (!err) > err = shutdown_cache(s); >