This reverts commit 96f1c58d853497a757463e0b57fed140d6858f3a
because it is no longer needed after "memcg: make sure that memcg is not
offline when charging" which makes sure that no charges will be accepted
after mem_cgroup_reparent_charges has started.
Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
---
mm/memcontrol.c | 36 ------------------------------------
1 file changed, 36 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 46b9f461cedf..6226977d53d0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6623,42 +6623,6 @@ 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. Offlining only happens to
- * cgroups with no tasks in them but charges can show up
- * without any tasks from the swapin path when the target
- * memcg is looked up from the swapout record and not from the
- * current task as it usually is. A race like this can leak
- * charges and put pages with stale cgroup pointers into
- * circulation:
- *
- * #0 #1
- * lookup_swap_cgroup_id()
- * rcu_read_lock()
- * mem_cgroup_lookup()
- * 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
- *
- * The bulk of the charges are still moved in offline_css() to
- * avoid pinning a lot of pages in case a long-term reference
- * like a swapout record is deferring the css_free() to long
- * after offlining. But this makes sure we catch any charges
- * made after offlining:
- */
- mem_cgroup_reparent_charges(memcg);
memcg_destroy_kmem(memcg);
__mem_cgroup_free(memcg);
--
1.9.rc1
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