mm: memcg/slab: fix memory leak at non-root kmem_cache destroy
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 B. It leads to create a non-root kmem_cache for allocating memory. 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 <songmuchun@bytedance.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Shakeel Butt <shakeelb@google.com> Acked-by: Roman Gushchin <guro@fb.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Christoph Lameter <cl@linux.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/20200716165103.83462-1-songmuchun@bytedance.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -326,6 +326,14 @@ int slab_unmergeable(struct kmem_cache *s)
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if (s->refcount < 0)
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return 1;
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#ifdef CONFIG_MEMCG_KMEM
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/*
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* Skip the dying kmem_cache.
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*/
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if (s->memcg_params.dying)
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return 1;
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#endif
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return 0;
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}
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@ -886,12 +894,15 @@ static int shutdown_memcg_caches(struct kmem_cache *s)
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return 0;
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}
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static void flush_memcg_workqueue(struct kmem_cache *s)
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static void memcg_set_kmem_cache_dying(struct kmem_cache *s)
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{
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spin_lock_irq(&memcg_kmem_wq_lock);
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s->memcg_params.dying = true;
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spin_unlock_irq(&memcg_kmem_wq_lock);
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}
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static void flush_memcg_workqueue(struct kmem_cache *s)
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{
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/*
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* SLAB and SLUB deactivate the kmem_caches through call_rcu. Make
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* sure all registered rcu callbacks have been invoked.
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@ -923,10 +934,6 @@ static inline int shutdown_memcg_caches(struct kmem_cache *s)
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{
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return 0;
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}
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static inline void flush_memcg_workqueue(struct kmem_cache *s)
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{
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}
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#endif /* CONFIG_MEMCG_KMEM */
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void slab_kmem_cache_release(struct kmem_cache *s)
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@ -944,8 +951,6 @@ void kmem_cache_destroy(struct kmem_cache *s)
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if (unlikely(!s))
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return;
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flush_memcg_workqueue(s);
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get_online_cpus();
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get_online_mems();
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@ -955,6 +960,22 @@ void kmem_cache_destroy(struct kmem_cache *s)
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if (s->refcount)
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goto out_unlock;
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#ifdef CONFIG_MEMCG_KMEM
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memcg_set_kmem_cache_dying(s);
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mutex_unlock(&slab_mutex);
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put_online_mems();
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put_online_cpus();
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flush_memcg_workqueue(s);
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get_online_cpus();
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get_online_mems();
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mutex_lock(&slab_mutex);
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#endif
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err = shutdown_memcg_caches(s);
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if (!err)
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err = shutdown_cache(s);
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