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authorVladimir Davydov <vdavydov@parallels.com>2014-01-23 15:53:06 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-01-23 16:36:51 -0800
commitf8570263ee16eb1d5038b8e20d7db3a68bbb2b49 (patch)
tree06d54d7f5f357622604d1e8338478b906729409d /mm/slab.h
parentf717eb3abb5ea38f60e671dbfdbf512c2c93d22e (diff)
downloadlinux-f8570263ee16eb1d5038b8e20d7db3a68bbb2b49.tar.bz2
memcg, slab: RCU protect memcg_params for root caches
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 <vdavydov@parallels.com> Cc: Michal Hocko <mhocko@suse.cz> Cc: Glauber Costa <glommer@gmail.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Balbir Singh <bsingharora@gmail.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: Christoph Lameter <cl@linux.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/slab.h')
-rw-r--r--mm/slab.h16
1 files changed, 15 insertions, 1 deletions
diff --git a/mm/slab.h b/mm/slab.h
index 72d1f9df71bd..8184a7cde272 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -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