From f8570263ee16eb1d5038b8e20d7db3a68bbb2b49 Mon Sep 17 00:00:00 2001 From: Vladimir Davydov Date: Thu, 23 Jan 2014 15:53:06 -0800 Subject: 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 Cc: Michal Hocko Cc: Glauber Costa Cc: Johannes Weiner Cc: Balbir Singh Cc: KAMEZAWA Hiroyuki Cc: Pekka Enberg Cc: Christoph Lameter Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memcontrol.c | 15 ++++++++------- mm/slab.h | 16 +++++++++++++++- 2 files changed, 23 insertions(+), 8 deletions(-) (limited to 'mm') diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 80197e54476..216659d4441 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 72d1f9df71b..8184a7cde27 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 -- cgit v1.2.3-70-g09d2