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Commit d9c10ddd authored by Michal Hocko's avatar Michal Hocko Committed by Tejun Heo
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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: default avatarLi Zefan <lizefan@huawei.com>
Signed-off-by: default avatarMichal Hocko <mhocko@suse.cz>
Acked-by: default avatarGlauber Costa <glommer@parallels.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 1e2ccd1c

mm/memcontrol.c

+32 −31
Original line number Diff line number Diff line
@@ -3214,52 +3214,53 @@ void mem_cgroup_destroy_cache(struct kmem_cache *cachep) 
	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;

}

/*

 * 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

 * allow them to see NULL, in which case the root memcg will be selected.

 *

 * We need this lock because multiple allocations to the same cache from a non

 * 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)

{

	char *name;

	struct kmem_cache *new;

	static char *tmp_name = NULL;



	lockdep_assert_held(&memcg_cache_mutex);



	name = memcg_cache_name(memcg, s);

	if (!name)

	/*

	 * 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;

	}



	new = kmem_cache_create_memcg(memcg, name, s->object_size, s->align,

	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;



	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

 * allow them to see NULL, in which case the root memcg will be selected.

 *

 * We need this lock because multiple allocations to the same cache from a non

 * will span more than one worker. Only one of them can create the cache.

 */

static DEFINE_MUTEX(memcg_cache_mutex);

static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,

						  struct kmem_cache *cachep)

{