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 5B619C433E0 for ; Wed, 15 Jul 2020 15:14:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3028D20658 for ; Wed, 15 Jul 2020 15:14:01 +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="lXIVAkey" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726633AbgGOPN7 (ORCPT ); Wed, 15 Jul 2020 11:13:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58332 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725932AbgGOPN7 (ORCPT ); Wed, 15 Jul 2020 11:13:59 -0400 Received: from mail-pf1-x442.google.com (mail-pf1-x442.google.com [IPv6:2607:f8b0:4864:20::442]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 16F52C061755 for ; Wed, 15 Jul 2020 08:13:59 -0700 (PDT) Received: by mail-pf1-x442.google.com with SMTP id m9so2235729pfh.0 for ; Wed, 15 Jul 2020 08:13:59 -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=0r5bb0ZMWMeJxc6MpJgS1kjFqz/n/TBIUkKDAK8VCUM=; b=lXIVAkeyGU3/B9G+hN1tCKgp85EQHsHi8oOUtcSkVV9Z0LcFVkKyWbelTBYEI6TU1m bhOBvmTOrlemvaEshedkWQ9SfdcZGA//kuKxWWiJIKG0uQw0Ijfi/LZoVEGx1aK0Sj+d Sy8cyeK/K0QL9vQatJhzlSw4YxH4SIDq91ibsAZyc9BI3s8dzw7ubsByrvKmSmjnr2Uj 710q8G5KWB+2mFkHJ1dNQISBcekeHsukednXGe8l9KZnul1rnJJ92TXao6hLiGtAQeBE Zx+K5CPbG3lgsoY4TTkXF2tM7tsNqwcmjtw2n1+0yift8fEdwoqGsZXooTiShVTbH4ft CCXg== 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=0r5bb0ZMWMeJxc6MpJgS1kjFqz/n/TBIUkKDAK8VCUM=; b=Cx/NgD0Yn3uqgrnoeqWRvMibqd7Itlow1QlKigjvBc6oSc6Hx3SiPobOXfi0JX+eoG C/JnE5C+9qRokJBM3XoC/gbqdsogei3stIVFCuj4l5fdUYr9qDey5yVLXtVg/B3AHwJw 6/7XUkasEzc7OW7GVtA3DGCUXZm2Q8+nk00xexWJQgfu2jeVGy+zrJai32S7j1AB8+Dz RxggvORGcn8bVN5fq+9Q+1S3ttDxyRTR06uV2/8EFf0hPfa+IQ4nFD3nuv82nJRQOCLk pybv5hGeqjOzhX5BOCsFB0PH8W+4pt9z/JRUWSOJAp4AK1Br2ZJ4BiZXJp5NeH40IlHm gRiA== X-Gm-Message-State: AOAM533Ho+kPWZYt69+U0lHdmvuIaLr+oUQMwU1htuErY1jS3tBbLWcH xzB48oE4iHf6mw1745mbJSGVRQ1fF8pC20B9UQsOGQ== X-Google-Smtp-Source: ABdhPJwaqBwFm70w6USx9FK6Q52mOCQdGHjx14sdVsxuDJX8FDJYRZUjwKajpLIuZPmZUIxALRCJQ+Ps3mhkf19NyDA= X-Received: by 2002:aa7:858c:: with SMTP id w12mr9910141pfn.143.1594826038426; Wed, 15 Jul 2020 08:13:58 -0700 (PDT) MIME-Version: 1.0 References: <20200707062754.8383-1-songmuchun@bytedance.com> <3d06418e-e75c-e7b8-91cd-ba56283045be@suse.cz> In-Reply-To: <3d06418e-e75c-e7b8-91cd-ba56283045be@suse.cz> From: Muchun Song Date: Wed, 15 Jul 2020 23:13:22 +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: Vlastimil Babka Cc: Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Linux Memory Management List , LKML , Shakeel Butt , Roman Gushchin 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 Wed, Jul 15, 2020 at 7:32 PM 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. > > 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+ ? Because the memcg slab/slub is reworked by Roman since v5.8. Therefore, this problem exists in v5.7 and below. > > > --- > > 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