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Subject[BUGFIX][PATCH] memcg: get/put parents at create/free
This version works well in my test.

Andrew, please pick up this one.

===
From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

The lifetime of struct cgroup and struct mem_cgroup is different and
mem_cgroup has its own reference count for handling references from swap_cgroup.

This causes strange problem that the parent mem_cgroup dies while
child mem_cgroup alive, and this problem causes a bug in case of use_hierarchy==1
because res_counter_uncharge climbs up the tree.

This patch is for avoiding it by getting the parent at create, and
putting it at freeing.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reviewed-by; KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
mm/memcontrol.c | 23 ++++++++++++++++++++++-
1 files changed, 22 insertions(+), 1 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index fb62b43..45e1b51 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -202,6 +202,8 @@ pcg_default_flags[NR_CHARGE_TYPE] = {

static void mem_cgroup_get(struct mem_cgroup *mem);
static void mem_cgroup_put(struct mem_cgroup *mem);
+static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem);
+static void mem_cgroup_get_parent(struct mem_cgroup *mem);

static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
struct page_cgroup *pc,
@@ -2185,10 +2187,28 @@ static void mem_cgroup_get(struct mem_cgroup *mem)

static void mem_cgroup_put(struct mem_cgroup *mem)
{
- if (atomic_dec_and_test(&mem->refcnt))
+ if (atomic_dec_and_test(&mem->refcnt)) {
+ struct mem_cgroup *parent = parent_mem_cgroup(mem);
__mem_cgroup_free(mem);
+ if (parent)
+ mem_cgroup_put(parent);
+ }
+}
+
+static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem)
+{
+ if (!mem->res.parent)
+ return NULL;
+ return mem_cgroup_from_res_counter(mem->res.parent, res);
}

+static void mem_cgroup_get_parent(struct mem_cgroup *mem)
+{
+ struct mem_cgroup *parent = parent_mem_cgroup(mem);
+
+ if (parent)
+ mem_cgroup_get(parent);
+}

#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
static void __init enable_swap_cgroup(void)
@@ -2237,6 +2257,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
if (parent)
mem->swappiness = get_swappiness(parent);
atomic_set(&mem->refcnt, 1);
+ mem_cgroup_get_parent(mem);
return &mem->css;
free_out:
__mem_cgroup_free(mem);


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