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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: Daisuke 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Daisuke Nishimura 2009-01-29 14:25:11 -08:00 committed by Linus Torvalds
parent baef99a08a
commit 7bcc1bb123
1 changed files with 22 additions and 1 deletions
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23
mm/memcontrol.c
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@ -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);