[PATCH 4.19 76/86] mm: memcg/slab: fix memory leak at non-root kmem_cache destroy

Greg Kroah-Hartman
2020-07-27T14:37:48Z

From: Muchun Song <songmuchun@bytedance.com>

commit d38a2b7a9c939e6d7329ab92b96559ccebf7b135 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -310,6 +310,14 @@ 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;
}

@@ -832,12 +840,15 @@ 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)
{
mutex_lock(&slab_mutex);
s->memcg_params.dying = true;
mutex_unlock(&slab_mutex);
+}

+static void flush_memcg_workqueue(struct kmem_cache *s)
+{
/*
* SLUB deactivates the kmem_caches through call_rcu_sched. Make
* sure all registered rcu callbacks have been invoked.
@@ -858,10 +869,6 @@ 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)
@@ -879,8 +886,6 @@ void kmem_cache_destroy(struct kmem_cach
if (unlikely(!s))
return;

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

@@ -890,6 +895,22 @@ 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);