mm/memcg_memfs_info: fix potential oom_lock recursion deadlock

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6ADCF
CVE: NA

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

syzbot is reporting GFP_KERNEL allocation with oom_lock held when
reporting memcg OOM [1]. If this allocation triggers the global OOM
situation then the system can livelock because the GFP_KERNEL
allocation with oom_lock held cannot trigger the global OOM killer
because __alloc_pages_may_oom() fails to hold oom_lock.

The problem mentioned above has been fixed by patch[2]. The is the same
problem in memcg_memfs_info feature too. Refer to the patch[2], fix it by
removing the allocation from mem_cgroup_print_memfs_info() completely,
and pass static buffer when calling from memcg OOM path.

Link: https://syzkaller.appspot.com/bug?extid=2d2aeadc6ce1e1f11d45 [1]
Link: https://lkml.kernel.org/r/86afb39f-8c65-bec2-6cfc-c5e3cd600c0b@I-love.SAKURA.ne.jp

 [2]
Fixes: 6b1d4d3a ("mm/memcg_memfs_info: show files that having pages charged in mem_cgroup")
Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Cai Xinchen <caixinchen1@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>