First, in memcg_create_kmem_cache() we should issue the write barrier
after the kmem_cache is initialized, but before storing the pointer to
it in its parent's memcg_params.
Second, we should always issue the read barrier after
cache_from_memcg_idx() to conform with the write barrier.
Third, its better to use smp_* versions of barriers, because we don't
need them on UP systems.
Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Glauber Costa <glommer@xxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 24 ++++++++++--------------
mm/slab.h | 6 +++++-
2 files changed, 15 insertions(+), 15 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e6ad6ff..e37fdb5 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3429,12 +3429,14 @@ static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
atomic_set(&new_cachep->memcg_params->nr_pages , 0);
- cachep->memcg_params->memcg_caches[idx] = new_cachep;
/*
- * 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();
+
+ cachep->memcg_params->memcg_caches[idx] = new_cachep;
out:
mutex_unlock(&memcg_cache_mutex);
return new_cachep;
@@ -3573,7 +3575,7 @@ 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);
@@ -3587,15 +3589,9 @@ 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;
}
diff --git a/mm/slab.h b/mm/slab.h
index 0859c42..1d8b53f 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -163,9 +163,13 @@ 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];
+ smp_read_barrier_depends(); /* see memcg_register_cache() */
+ return cachep;
}
static inline struct kmem_cache *memcg_root_cache(struct kmem_cache *s)
--
1.7.10.4
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