On Thu 21-03-13 10:08:49, Michal Hocko wrote: > On Thu 21-03-13 09:22:21, Li Zefan wrote: > > As cgroup supports rename, it's unsafe to dereference dentry->d_name > > without proper vfs locks. Fix this by using cgroup_name(). > > > > Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx> > > --- > > > > This patch depends on "cgroup: fix cgroup_path() vs rename() race", > > which has been queued for 3.10. > > > > --- > > mm/memcontrol.c | 15 +++++++-------- > > 1 file changed, 7 insertions(+), 8 deletions(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index 53b8201..72be5c9 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -3217,17 +3217,16 @@ void mem_cgroup_destroy_cache(struct kmem_cache *cachep) > > static char *memcg_cache_name(struct mem_cgroup *memcg, struct kmem_cache *s) > > { > > char *name; > > - struct dentry *dentry; > > + > > + name = (char *)__get_free_page(GFP_TEMPORARY); > > Ouch. Can we use a static temporary buffer instead? > This is called from workqueue context so we do not have to be afraid > of the deep call chain. Bahh, I was thinking about two things at the same time and that is how it ends... I meant a temporary buffer on the stack. But a separate allocation sounds even easier. > It is also not a hot path AFAICS. > > Even GFP_ATOMIC for kasprintf would be an improvement IMO. What about the following (not even compile tested because I do not have cgroup_name in my tree yet): --- diff --git a/mm/memcontrol.c b/mm/memcontrol.c index f608546..ede0382 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3370,13 +3370,18 @@ static char *memcg_cache_name(struct mem_cgroup *memcg, struct kmem_cache *s) struct dentry *dentry; rcu_read_lock(); - dentry = rcu_dereference(memcg->css.cgroup->dentry); + name = kasprintf(GFP_ATOMIC, "%s(%d:%s)", s->name, + memcg_cache_id(memcg), cgroup_name(memcg->css.cgroup)); rcu_read_unlock(); - BUG_ON(dentry == NULL); - - name = kasprintf(GFP_KERNEL, "%s(%d:%s)", s->name, - memcg_cache_id(memcg), dentry->d_name.name); + if (!name) { + name = kmalloc(PAGE_SIZE, GFP_KERNEL); + rcu_read_lock(); + name = snprintf(name, PAGE_SIZE, "%s(%d:%s)", s->name, + memcg_cache_id(memcg), + cgroup_name(memcg->css.cgroup)); + rcu_read_unlock(); + } return name; } -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>