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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=PoeyZrLh5bJ+dTlPUqXbkinGw1VjKLjid8QVnEJlxm/8hA0mlQ6FMLWgPpxDctPZ4g blBzCXPdHoAEj8WPvl/oEN9wJ6nPOQr+k+OSIk7/CqgujLQoXCvPlNfDvhUM0LeyU8u6 KOJ7stTzfJiDSwrsPOe8hYv9dwa6P12qZHwayytM0TB21uFYTDqu+iQuOX1a5ETFzMGe w07iaudv/CQ3pBG+X9pWQLsbohFT4jGoDSyofz7eFQt2xQK/LlHzK/GGEvVqTfsEdZ0X iwIHdvx7Ozhq4yAYrDYXdNFjR7NuA2D8Is60FOVWYVllqY2FQr5YENtaARMh55vdFTLp QugQ== X-Gm-Message-State: AOAM530DPqDBERqdXhYlXN8zAi6Lyi15ow0/WnzuDOY2BzjDXkzBYSU1 5V5adTzJ3mhR4WYXfIxjItPbAx73SELQnZnNNUEGAA== 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" X-Rspamd-Queue-Id: 43169100ED9D5 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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