On Tue, Jun 4, 2019 at 7:45 PM Roman Gushchin <guro@xxxxxx> wrote: > > Johannes noticed that reading the memcg kmem_cache pointer in > cache_from_memcg_idx() is performed using READ_ONCE() macro, > which doesn't implement a SMP barrier, which is required > by the logic. > > Add a proper smp_rmb() to be paired with smp_wmb() in > memcg_create_kmem_cache(). > > The same applies to memcg_create_kmem_cache() itself, > which reads the same value without barriers and READ_ONCE(). > > Suggested-by: Johannes Weiner <hannes@xxxxxxxxxxx> > Signed-off-by: Roman Gushchin <guro@xxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> This seems like independent to the series. Shouldn't this be Cc'ed stable? > --- > mm/slab.h | 1 + > mm/slab_common.c | 3 ++- > 2 files changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/slab.h b/mm/slab.h > index 739099af6cbb..1176b61bb8fc 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -260,6 +260,7 @@ cache_from_memcg_idx(struct kmem_cache *s, int idx) > * memcg_caches issues a write barrier to match this (see > * memcg_create_kmem_cache()). > */ > + smp_rmb(); > cachep = READ_ONCE(arr->entries[idx]); > rcu_read_unlock(); > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 58251ba63e4a..8092bdfc05d5 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -652,7 +652,8 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg, > * allocation (see memcg_kmem_get_cache()), several threads can try to > * create the same cache, but only one of them may succeed. > */ > - if (arr->entries[idx]) > + smp_rmb(); > + if (READ_ONCE(arr->entries[idx])) > goto out_unlock; > > cgroup_name(css->cgroup, memcg_name_buf, sizeof(memcg_name_buf)); > -- > 2.20.1 >
