Re: [PATCH] memcg: don't do cleanup manually if mem_cgroup_css_online() fails

Michal Hocko
2013-04-02T12:16:00Z

On Tue 02-04-13 15:35:28, Li Zefan wrote:
[...]
> @@ -6247,16 +6247,7 @@ mem_cgroup_css_online(struct cgroup *cont)
>
> error = memcg_init_kmem(memcg, &mem_cgroup_subsys);
> mutex_unlock(&memcg_create_mutex);
> - if (error) {
> - /*
> - * We call put now because our (and parent's) refcnts
> - * are already in place. mem_cgroup_put() will internally
> - * call __mem_cgroup_free, so return directly
> - */
> - mem_cgroup_put(memcg);
> - if (parent->use_hierarchy)
> - mem_cgroup_put(parent);
> - }
> +
> return error;
> }

The mem_cgroup_put(parent) part is incorrect because mem_cgroup_put goes
up the hierarchy already but I do not think mem_cgroup_put(memcg) should
go away as well. Who is going to free the last reference then?

Maybe I am missing something but we have:
cgroup_create
css = ss->css_alloc(cgrp)
mem_cgroup_css_alloc
atomic_set(&memcg->refcnt, 1)
online_css(ss, cgrp)
mem_cgroup_css_online
error = memcg_init_kmem # fails
goto err_destroy
err_destroy:
cgroup_destroy_locked(cgrp)
offline_css
mem_cgroup_css_offline

no mem_cgroup_put on the way.

--
Michal Hocko
SUSE Labs