cgroup: Fix task_css_check rcu warnings

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4OF4N



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task_css() should be protected by rcu. In my environment
if not protected by rcu qemu may fail to start.

Fixes: a885e3f9 ("psi: support psi under cgroup v1")
Reported-by: Yang Yingliang <yangyingliang@huawei.com>
Acked-by: Michael Wang <yun.wany@linux.alibaba.com>
Signed-off-by: Xunlei Pang <xlpang@linux.alibaba.com>
Signed-off-by: Yihao Wu <wuyihao@linux.alibaba.com>
Acked-by: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: Chen Wandun <chenwandun@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>