Revert "memcg: fix a UAF problem in drain_all_stock()"

hulk inclusion
category: bugfix
bugzilla: 189183, https://gitee.com/openeuler/kernel/issues/I7Z1ZU


CVE: NA

--------------------------------

This reverts commit 616e7082 ("memcg: fix a UAF problem in
drain_all_stock()"), which was produced based on in-house 3.10 and later
was found to be not suitable for in-house 4.18/4.19, as both of them use
async version of drain_all_stock() whose actual draining could be
delayed, and some of them even removed drain_all_stock() from memcg's
offline process. In these cases the commit doesn't fix the original
problem.

Fixes: 616e7082 ("memcg: fix a UAF problem in drain_all_stock()")
Signed-off-by: GONG, Ruiqi <gongruiqi1@huawei.com>