The patch titled Subject: mm: memcg/slab: fix memory leak at non-root kmem_cache destroy has been added to the -mm tree. Its filename is mm-memcg-slab-fix-memory-leak-at-non-root-kmem_cache-destroy.patch

This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-memcg-slab-fix-memory-leak-at-no... and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-memcg-slab-fix-memory-leak-at-no...

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------------------------------------------------------ From: Muchun Song songmuchun@bytedance.com Subject: 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.

Link: http://lkml.kernel.org/r/20200716165103.83462-1-songmuchun@bytedance.com Fixes: 92ee383f6daa ("mm: fix race between kmem_cache destroy, create and deactivate") Signed-off-by: Muchun Song songmuchun@bytedance.com 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 Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/slab_common.c | 35 ++++++++++++++++++++++++++++------- 1 file changed, 28 insertions(+), 7 deletions(-)

--- a/mm/slab_common.c~mm-memcg-slab-fix-memory-leak-at-non-root-kmem_cache-destroy +++ a/mm/slab_common.c @@ -326,6 +326,14 @@ int slab_unmergeable(struct kmem_cache * if (s->refcount < 0) return 1;

+#ifdef CONFIG_MEMCG_KMEM + /* + * Skip the dying kmem_cache. + */ + if (s->memcg_params.dying) + return 1; +#endif + return 0; }

@@ -886,12 +894,15 @@ static int shutdown_memcg_caches(struct return 0; }

-static void flush_memcg_workqueue(struct kmem_cache *s) +static void memcg_set_kmem_cache_dying(struct kmem_cache *s) { spin_lock_irq(&memcg_kmem_wq_lock); s->memcg_params.dying = true; spin_unlock_irq(&memcg_kmem_wq_lock); +}

+static void flush_memcg_workqueue(struct kmem_cache *s) +{ /* * SLAB and SLUB deactivate the kmem_caches through call_rcu. Make * sure all registered rcu callbacks have been invoked. @@ -923,10 +934,6 @@ static inline int shutdown_memcg_caches( { return 0; } - -static inline void flush_memcg_workqueue(struct kmem_cache *s) -{ -} #endif /* CONFIG_MEMCG_KMEM */

void slab_kmem_cache_release(struct kmem_cache *s) @@ -944,8 +951,6 @@ void kmem_cache_destroy(struct kmem_cach if (unlikely(!s)) return;

- flush_memcg_workqueue(s); - get_online_cpus(); get_online_mems();

@@ -955,6 +960,22 @@ void kmem_cache_destroy(struct kmem_cach if (s->refcount) goto out_unlock;

+#ifdef CONFIG_MEMCG_KMEM + memcg_set_kmem_cache_dying(s); + + mutex_unlock(&slab_mutex); + + put_online_mems(); + put_online_cpus(); + + flush_memcg_workqueue(s); + + get_online_cpus(); + get_online_mems(); + + mutex_lock(&slab_mutex); +#endif + err = shutdown_memcg_caches(s); if (!err) err = shutdown_cache(s); _

Patches currently in -mm which might be from songmuchun@bytedance.com are

mm-memcg-slab-fix-memory-leak-at-non-root-kmem_cache-destroy.patch mm-page_alloc-skip-setting-nodemask-when-we-are-in-interrupt.patch