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memcg, slab: RCU protect memcg_params for root caches

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We relocate root cache's memcg_params whenever we need to grow the
memcg_caches array to accommodate all kmem-active memory cgroups.
Currently on relocation we free the old version immediately, which can
lead to use-after-free, because the memcg_caches array is accessed
lock-free (see cache_from_memcg_idx()).  This patch fixes this by making
memcg_params RCU-protected for root caches.

Signed-off-by: Vladimir Davydov <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Glauber Costa <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Christoph Lameter <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Vladimir Davydov 2014-01-23 15:53:06 -08:00 • committed by Linus Torvalds
commit f8570263ee
3 changed files with 30 additions and 10 deletions
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16
mm/slab.h
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@ -160,14 +160,28 @@ static inline const char *cache_name(struct kmem_cache *s)
return s->name;
}
/*
* Note, we protect with RCU only the memcg_caches array, not per-memcg caches.
* That said the caller must assure the memcg's cache won't go away. Since once
* created a memcg's cache is destroyed only along with the root cache, it is
* true if we are going to allocate from the cache or hold a reference to the
* root cache by other means. Otherwise, we should hold either the slab_mutex
* or the memcg's slab_caches_mutex while calling this function and accessing
* the returned value.
*/
static inline struct kmem_cache *
cache_from_memcg_idx(struct kmem_cache *s, int idx)
{
struct kmem_cache *cachep;
struct memcg_cache_params *params;
if (!s->memcg_params)
return NULL;
cachep = s->memcg_params->memcg_caches[idx];
rcu_read_lock();
params = rcu_dereference(s->memcg_params);
cachep = params->memcg_caches[idx];
rcu_read_unlock();
/*
* Make sure we will access the up-to-date value. The code updating