Commit 7bcc1bb1 authored by Daisuke Nishimura's avatar Daisuke Nishimura Committed by Linus Torvalds
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memcg: get/put parents at create/free 



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: default avatarDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reviewed-by; KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent baef99a0

mm/memcontrol.c

+22 −1
Original line number Diff line number Diff line
@@ -202,6 +202,7 @@ 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_charge_statistics(struct mem_cgroup *mem,

					 struct page_cgroup *pc,
@@ -2193,10 +2194,23 @@ 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);

	}

}



/*

 * Returns the parent mem_cgroup in memcgroup hierarchy with hierarchy enabled.

 */

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);

}



#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP

static void __init enable_swap_cgroup(void)
@@ -2235,6 +2249,13 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont) 
	if (parent && parent->use_hierarchy) {

		res_counter_init(&mem->res, &parent->res);

		res_counter_init(&mem->memsw, &parent->memsw);

		/*

		 * We increment refcnt of the parent to ensure that we can

		 * safely access it on res_counter_charge/uncharge.

		 * This refcnt will be decremented when freeing this

		 * mem_cgroup(see mem_cgroup_put).

		 */

		mem_cgroup_get(parent);

	} else {

		res_counter_init(&mem->res, NULL);

		res_counter_init(&mem->memsw, NULL);

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