On Tue, Jul 28, 2020 at 08:56:41PM +0800, Muchun Song wrote:
On Mon, Jul 27, 2020 at 10:12 PM Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
From: Muchun Song <songmuchun@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Acked-by: Roman Gushchin <guro@xxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20200716165103.83462-1-songmuchun@xxxxxxxxxxxxx
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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);
We should remove mutex_lock/unlock(&slab_mutex) here, because
we already hold the slab_mutex from kmem_cache_destroy().
Good catch! I backported 63b02ef7dc4e ("mm: memcg/slab: synchronize
access to kmem_cache dying flag using a spinlock") instead of changing
this patch.
--
Thanks,
Sasha
