memcg: fix memcg_cache_name() to use cgroup_name()
As cgroup supports rename, it's unsafe to dereference dentry->d_name
without proper vfs locks. Fix this by using cgroup_name() rather than
dentry directly.
Also open code memcg_cache_name because it is called only from
kmem_cache_dup which frees the returned name right after
kmem_cache_create_memcg makes a copy of it. Such a short-lived
allocation doesn't make too much sense. So replace it by a static
buffer as kmem_cache_dup is called with memcg_cache_mutex.
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Glauber Costa <glommer@parallels.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 53b8201..9715c0c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3214,43 +3214,6 @@
schedule_work(&cachep->memcg_params->destroy);
}
-static char *memcg_cache_name(struct mem_cgroup *memcg, struct kmem_cache *s)
-{
- char *name;
- struct dentry *dentry;
-
- rcu_read_lock();
- dentry = rcu_dereference(memcg->css.cgroup->dentry);
- rcu_read_unlock();
-
- BUG_ON(dentry == NULL);
-
- name = kasprintf(GFP_KERNEL, "%s(%d:%s)", s->name,
- memcg_cache_id(memcg), dentry->d_name.name);
-
- return name;
-}
-
-static struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
- struct kmem_cache *s)
-{
- char *name;
- struct kmem_cache *new;
-
- name = memcg_cache_name(memcg, s);
- if (!name)
- return NULL;
-
- new = kmem_cache_create_memcg(memcg, name, s->object_size, s->align,
- (s->flags & ~SLAB_PANIC), s->ctor, s);
-
- if (new)
- new->allocflags |= __GFP_KMEMCG;
-
- kfree(name);
- return new;
-}
-
/*
* This lock protects updaters, not readers. We want readers to be as fast as
* they can, and they will either see NULL or a valid cache value. Our model
@@ -3260,6 +3223,44 @@
* will span more than one worker. Only one of them can create the cache.
*/
static DEFINE_MUTEX(memcg_cache_mutex);
+
+/*
+ * Called with memcg_cache_mutex held
+ */
+static struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
+ struct kmem_cache *s)
+{
+ struct kmem_cache *new;
+ static char *tmp_name = NULL;
+
+ lockdep_assert_held(&memcg_cache_mutex);
+
+ /*
+ * kmem_cache_create_memcg duplicates the given name and
+ * cgroup_name for this name requires RCU context.
+ * This static temporary buffer is used to prevent from
+ * pointless shortliving allocation.
+ */
+ if (!tmp_name) {
+ tmp_name = kmalloc(PATH_MAX, GFP_KERNEL);
+ if (!tmp_name)
+ return NULL;
+ }
+
+ rcu_read_lock();
+ snprintf(tmp_name, PATH_MAX, "%s(%d:%s)", s->name,
+ memcg_cache_id(memcg), cgroup_name(memcg->css.cgroup));
+ rcu_read_unlock();
+
+ new = kmem_cache_create_memcg(memcg, tmp_name, s->object_size, s->align,
+ (s->flags & ~SLAB_PANIC), s->ctor, s);
+
+ if (new)
+ new->allocflags |= __GFP_KMEMCG;
+
+ return new;
+}
+
static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
struct kmem_cache *cachep)
{