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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 <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>
This commit is contained in:
Vladimir Davydov 2014-01-23 15:53:06 -08:00 committed by Linus Torvalds
parent f717eb3abb
commit f8570263ee
3 changed files with 30 additions and 10 deletions
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9
include/linux/slab.h
View File

@ -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;

15
mm/memcontrol.c
View File

@ -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;
}

16
mm/slab.h
View File

@ -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