There is an imbalance between when slab_pre_alloc_hook calls
memcg_kmem_get_cache and when slab_post_alloc_hook calls
memcg_kmem_put_cache.
This can cause a memcg kmem cache to be destroyed right as
an object from that cache is being allocated, which is probably
not good. It could lead to things like a memcg allocating new
kmalloc slabs instead of using freed space in old ones, maybe
memory leaks, and maybe oopses as a memcg kmalloc slab is getting
destroyed on one CPU while another CPU is trying to do an allocation
from that same memcg.
The obvious fix would be to use the same condition for calling
memcg_kmem_put_cache that we also use to decide whether to call
memcg_kmem_get_cache.
I am not sure how long this bug has been around, since the last
changeset to touch that code - 452647784b2f ("mm: memcontrol: cleanup
kmem charge functions") - merely moved the bug from one location to
another. I am still tagging that changeset, because the fix should
automatically apply that far back.
Signed-off-by: Rik van Riel <[email protected]>
Fixes: 452647784b2f ("mm: memcontrol: cleanup kmem charge functions")
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Alexey Dobriyan <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Tejun Heo <[email protected]>
---
mm/slab.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/slab.h b/mm/slab.h
index 4190c24ef0e9..ab3d95bef8a0 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -444,7 +444,8 @@ static inline void slab_post_alloc_hook(struct kmem_cache
*s, gfp_t flags,
p[i] = kasan_slab_alloc(s, object, flags);
}
- if (memcg_kmem_enabled())
+ if (memcg_kmem_enabled() &&
+ ((flags & __GFP_ACCOUNT) || (s->flags & SLAB_ACCOUNT)))
memcg_kmem_put_cache(s);
}
--
2.17.1
