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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: 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>
This commit is contained in:
Michal Hocko 2013-03-28 08:48:14 +01:00 committed by Tejun Heo
parent 1e2ccd1c0f
commit d9c10ddddc
1 changed files with 38 additions and 37 deletions
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75
mm/memcontrol.c
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@ -3214,43 +3214,6 @@ 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;
}
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 @@ static struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
* 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)
{