diff options
author | Vladimir Davydov <vdavydov@parallels.com> | 2014-01-23 15:52:59 -0800 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-01-23 16:36:51 -0800 |
commit | 959c8963fc6c8c9b97e80c55ce77105247040e7d (patch) | |
tree | 4f2bcf3e4a69f4a655fabf0fc178498f3d0c367f | |
parent | 1aa13254259bdef0bca723849ab3bab308d2f0c3 (diff) | |
download | op-kernel-dev-959c8963fc6c8c9b97e80c55ce77105247040e7d.zip op-kernel-dev-959c8963fc6c8c9b97e80c55ce77105247040e7d.tar.gz |
memcg, slab: fix barrier usage when accessing memcg_caches
Each root kmem_cache has pointers to per-memcg caches stored in its
memcg_params::memcg_caches array. Whenever we want to allocate a slab
for a memcg, we access this array to get per-memcg cache to allocate
from (see memcg_kmem_get_cache()). The access must be lock-free for
performance reasons, so we should use barriers to assert the kmem_cache
is up-to-date.
First, we should place a write barrier immediately before setting the
pointer to it in the memcg_caches array in order to make sure nobody
will see a partially initialized object. Second, we should issue a read
barrier before dereferencing the pointer to conform to the write
barrier.
However, currently the barrier usage looks rather strange. We have a
write barrier *after* setting the pointer and a read barrier *before*
reading the pointer, which is incorrect. This patch fixes this.
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-- | mm/memcontrol.c | 24 | ||||
-rw-r--r-- | mm/slab.h | 12 |
2 files changed, 21 insertions, 15 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 739383c..322d18d 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3274,12 +3274,14 @@ void memcg_register_cache(struct kmem_cache *s) list_add(&s->memcg_params->list, &memcg->memcg_slab_caches); mutex_unlock(&memcg->slab_caches_mutex); - root->memcg_params->memcg_caches[id] = s; /* - * the readers won't lock, make sure everybody sees the updated value, - * so they won't put stuff in the queue again for no reason + * Since readers won't lock (see cache_from_memcg_idx()), we need a + * barrier here to ensure nobody will see the kmem_cache partially + * initialized. */ - wmb(); + smp_wmb(); + + root->memcg_params->memcg_caches[id] = s; } void memcg_unregister_cache(struct kmem_cache *s) @@ -3605,7 +3607,7 @@ struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp) { struct mem_cgroup *memcg; - int idx; + struct kmem_cache *memcg_cachep; VM_BUG_ON(!cachep->memcg_params); VM_BUG_ON(!cachep->memcg_params->is_root_cache); @@ -3619,15 +3621,9 @@ struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep, if (!memcg_can_account_kmem(memcg)) goto out; - idx = memcg_cache_id(memcg); - - /* - * barrier to mare sure we're always seeing the up to date value. The - * code updating memcg_caches will issue a write barrier to match this. - */ - read_barrier_depends(); - if (likely(cache_from_memcg_idx(cachep, idx))) { - cachep = cache_from_memcg_idx(cachep, idx); + memcg_cachep = cache_from_memcg_idx(cachep, memcg_cache_id(memcg)); + if (likely(memcg_cachep)) { + cachep = memcg_cachep; goto out; } @@ -163,9 +163,19 @@ static inline const char *cache_name(struct kmem_cache *s) static inline struct kmem_cache * cache_from_memcg_idx(struct kmem_cache *s, int idx) { + struct kmem_cache *cachep; + if (!s->memcg_params) return NULL; - return s->memcg_params->memcg_caches[idx]; + cachep = s->memcg_params->memcg_caches[idx]; + + /* + * Make sure we will access the up-to-date value. The code updating + * memcg_caches issues a write barrier to match this (see + * memcg_register_cache()). + */ + smp_read_barrier_depends(); + return cachep; } static inline struct kmem_cache *memcg_root_cache(struct kmem_cache *s) |