!2067 memcg: add refcnt for pcpu stock to avoid UAF problem in drain_all_stock()

Merge Pull Request from: @ci-robot 
 
PR sync from: "GONG, Ruiqi" <gongruiqi1@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/3LOG57FTUWBYXBMHHOL567ST5V3SGPNZ/ 
 
https://gitee.com/openeuler/kernel/issues/I7Z1ZU 
 
Link:https://gitee.com/openeuler/kernel/pulls/2067

 

Reviewed-by: Liu YongQiang <liuyongqiang13@huawei.com>
Reviewed-by: zhao xiaoqiang <zhaoxiaoqiang11@jd.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>