I am sorry, I have overlooked this patch.
On Thu 07-11-13 19:14:37, Johannes Weiner wrote:
[...]
> From: Johannes Weiner <hannes@xxxxxxxxxxx>
> Subject: [patch] mm: memcg: reparent charges during css_free()
>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: stable@xxxxxxxxxx # 3.8+
Acked-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> mm/memcontrol.c | 29 ++++++++++++++++++++++++++++-
> 1 file changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index cc4f9cbe760e..3dce2b50891c 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -6341,7 +6341,34 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
> static void mem_cgroup_css_free(struct cgroup_subsys_state *css)
> {
> struct mem_cgroup *memcg = mem_cgroup_from_css(css);
> -
> + /*
> + * XXX: css_offline() would be where we should reparent all
> + * memory to prepare the cgroup for destruction. However,
> + * memcg does not do css_tryget() and res_counter charging
> + * under the same RCU lock region, which means that charging
> + * could race with offlining, potentially leaking charges and
> + * sending out pages with stale cgroup pointers:
> + *
> + * #0 #1
> + * rcu_read_lock()
> + * css_tryget()
> + * rcu_read_unlock()
> + * disable css_tryget()
> + * call_rcu()
> + * offline_css()
> + * reparent_charges()
> + * res_counter_charge()
> + * css_put()
> + * css_free()
> + * pc->mem_cgroup = dead memcg
> + * add page to lru
> + *
> + * We still reparent most charges in offline_css() simply
> + * because we don't want all these pages stuck if a long-term
> + * reference like a swap entry is holding on to the cgroup
> + * past offlining, but make sure we catch any raced charges:
> + */
> + mem_cgroup_reparent_charges(memcg);
> memcg_destroy_kmem(memcg);
> __mem_cgroup_free(memcg);
> }
> --
> 1.8.4.2
>
--
Michal Hocko
SUSE Labs
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