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mm: memcg/slab: fix memory leak at non-root kmem_cache destroy 

commit d38a2b7a9c 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: 92ee383f6d ("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>
5.4-rM2-2.2.x-imx-squashed
Muchun Song 2020-07-23 21:15:27 -07:00 committed by Greg Kroah-Hartman
parent db949f60d9
commit 95750e1edb
1 changed files with 28 additions and 7 deletions
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35
mm/slab_common.c
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@ -326,6 +326,14 @@ int slab_unmergeable(struct kmem_cache *s)
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 kmem_cache *s)
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(struct kmem_cache *s)
{
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_cache *s)
if (unlikely(!s))
return;
flush_memcg_workqueue(s);
get_online_cpus();
get_online_mems();
@ -955,6 +960,22 @@ void kmem_cache_destroy(struct kmem_cache *s)
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);