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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
parentf717eb3abb5ea38f60e671dbfdbf512c2c93d22e (diff)
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>
-rw-r--r--include/linux/slab.h9
-rw-r--r--mm/memcontrol.c15
-rw-r--r--mm/slab.h16
3 files changed, 30 insertions, 10 deletions
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 1e2f4fe12773..a060142aa5f5 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -513,7 +513,9 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
*
* Both the root cache and the child caches will have it. For the root cache,
* this will hold a dynamically allocated array large enough to hold
- * information about the currently limited memcgs in the system.
+ * information about the currently limited memcgs in the system. To allow the
+ * array to be accessed without taking any locks, on relocation we free the old
+ * version only after a grace period.
*
* Child caches will hold extra metadata needed for its operation. Fields are:
*
@@ -528,7 +530,10 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
struct memcg_cache_params {
bool is_root_cache;
union {
- struct kmem_cache *memcg_caches[0];
+ struct {
+ struct rcu_head rcu_head;
+ struct kmem_cache *memcg_caches[0];
+ };
struct {
struct mem_cgroup *memcg;
struct list_head list;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 80197e544764..216659d4441a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3178,18 +3178,17 @@ int memcg_update_cache_size(struct kmem_cache *s, int num_groups)
if (num_groups > memcg_limited_groups_array_size) {
int i;
+ struct memcg_cache_params *new_params;
ssize_t size = memcg_caches_array_size(num_groups);
size *= sizeof(void *);
size += offsetof(struct memcg_cache_params, memcg_caches);
- s->memcg_params = kzalloc(size, GFP_KERNEL);
- if (!s->memcg_params) {
- s->memcg_params = cur_params;
+ new_params = kzalloc(size, GFP_KERNEL);
+ if (!new_params)
return -ENOMEM;
- }
- s->memcg_params->is_root_cache = true;
+ new_params->is_root_cache = true;
/*
* There is the chance it will be bigger than
@@ -3203,7 +3202,7 @@ int memcg_update_cache_size(struct kmem_cache *s, int num_groups)
for (i = 0; i < memcg_limited_groups_array_size; i++) {
if (!cur_params->memcg_caches[i])
continue;
- s->memcg_params->memcg_caches[i] =
+ new_params->memcg_caches[i] =
cur_params->memcg_caches[i];
}
@@ -3216,7 +3215,9 @@ int memcg_update_cache_size(struct kmem_cache *s, int num_groups)
* bigger than the others. And all updates will reset this
* anyway.
*/
- kfree(cur_params);
+ rcu_assign_pointer(s->memcg_params, new_params);
+ if (cur_params)
+ kfree_rcu(cur_params, rcu_head);
}
return 0;
}
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