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=-10.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 78F4FC433E1 for ; Wed, 15 Jul 2020 16:31:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5349C2065E for ; Wed, 15 Jul 2020 16:31:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=bytedance-com.20150623.gappssmtp.com header.i=@bytedance-com.20150623.gappssmtp.com header.b="uyXgsFd5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726843AbgGOQbo (ORCPT ); Wed, 15 Jul 2020 12:31:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42174 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725792AbgGOQbj (ORCPT ); Wed, 15 Jul 2020 12:31:39 -0400 Received: from mail-pf1-x443.google.com (mail-pf1-x443.google.com [IPv6:2607:f8b0:4864:20::443]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 25CD9C061755 for ; Wed, 15 Jul 2020 09:31:39 -0700 (PDT) Received: by mail-pf1-x443.google.com with SMTP id x72so2321983pfc.6 for ; Wed, 15 Jul 2020 09:31:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=53xi7g3puotGB363xy2OEXt6uuc0PRweN+NzFYccYkk=; b=uyXgsFd5yE0F3yTWoENRGh6XofWx6qEDC5ysullQoFZ4TlZApXCAZUsSkQJcKJSLpc tCaa1RS8UIbn8qmG39/lmXTGJAsqMK9V+gqdtH36JfsHjelGHd5nRvDrHB7cLerbmsgt uWp3W/RR1JSDRU9DV0VK1gILcgX0Ia+lybe3xV3anqWkaNdvudr7uhcDgmRG30HchXOs X3KfHMRbUj8qhEhhpv0fcLTGzds6B3Erxh0RDvCNf2AkPE9GhPtS7CflJWIMi2oC02LL 2Ztott/QVRz50ZqOTqld80XF1JCKg58bpPWOr5NkRNO5ZqFL639FKYdYtMau2UNxcQFN r2OQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=53xi7g3puotGB363xy2OEXt6uuc0PRweN+NzFYccYkk=; b=JxlnE7oZjFXFP9H+jklLAnPMaANc3TfSRs0Swnlco7SzvOn3jlNS/grHEXmA/fxW/E tj2Li+zAM4IMc2HqLUzrHArfdY8UDrshTZi0YsHPGmPbKzKJqoOuDopJyLJjJZ3HGSDf ZmzGyZ5pAzKt6ottSQRQIdn+QRYVxA2Z16TnID6aA04bOSzB0wBNlKDHXucag/pOMo+V fjwAZlyN0cMvmaBhoDbxPrgPj6U1kKrNAGqxCmoq/iVpU2uCSXh6Kt35aJ2qDVSzWdVI a1JufRtDu3NLpGXu+YR7RO8U+za4nRDD796bIjksTnUGsk1rh8oJcwGpXkCKhsv+chDe 3U4A== X-Gm-Message-State: AOAM533w7YLmpvU7iKRbPEOMQI26QZXSR1cBpJaJJVEX2KbuoU1k9Rvf v9DNLMtuIUHoUf0MenXNj3grW7JFGvxw14FOaBB0HA== X-Google-Smtp-Source: ABdhPJxUGp93WoplWQdqdBEzPCf01zWLhU2TGTWuQ1UTb/Kp9Zv/8T5yRUuQSVR/t1KT3ObYn2nEDfUFQWaP6ZKlbuc= X-Received: by 2002:a63:cf49:: with SMTP id b9mr446382pgj.31.1594830698604; Wed, 15 Jul 2020 09:31:38 -0700 (PDT) MIME-Version: 1.0 References: <20200707062754.8383-1-songmuchun@bytedance.com> <3d06418e-e75c-e7b8-91cd-ba56283045be@suse.cz> <20200715162445.GA4003@carbon.lan> In-Reply-To: <20200715162445.GA4003@carbon.lan> From: Muchun Song Date: Thu, 16 Jul 2020 00:31:02 +0800 Message-ID: Subject: Re: [External] Re: [PATCH v5.4.y, v4.19.y] mm: memcg/slab: fix memory leak at non-root kmem_cache destroy To: Roman Gushchin Cc: Vlastimil Babka , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Linux Memory Management List , LKML , Shakeel Butt Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 16, 2020 at 12:24 AM Roman Gushchin wrote: > > On Wed, Jul 15, 2020 at 01:32:00PM +0200, Vlastimil Babka wrote: > > 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. Hi Roman, I am sorry, here is a typo. I mean the step 4) allocates memory from the kmem_cache B instead of A. > > > 5) When destroy the memory cgroup created in the step 4), the > > > non-root kmem_cache can never be destroyed. > > Hello, Muchun! > > If the scenario above is accurate, it means that somebody is allocating > from the kmem_cache A (or it's memcg counterparts, doesn't matter) after > calling kmem_cache_destroy()? If so, it's an API violation, and the following > memory leak is a non-issue on the slab side. No one should allocate memory > after calling kmem_cache_destroy(). It has to be called after all outstanding > allocations are freed, and it should be literally the last operation > with the kmem_cache. > > Kmem_cache aliasing/sharing, as well as memcg accounting implementation are > implementation details and should not affect the picture. > > I wonder, did you see the problem in the wild? How does it look like? > Which kmem_cache is involved? Etc. > > BTW, Vlastimil is absolutely right about stable backports and rework planned > for 5.9, but let's figure out the problem first. > > Thank you! > > > > > > > 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); > > > > > -- Yours, Muchun