cgroup: Add missing cpus_read_lock() to cgroup_attach_task_all()

mainline inclusion
from mainline-v6.0-rc3
commit 43626dad
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6L46J
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=43626dade36fa74d3329046f4ae2d7fdefe401c6

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

syzbot is hitting percpu_rwsem_assert_held(&cpu_hotplug_lock) warning at
cpuset_attach() [1], for commit 4f7e7236 ("cgroup: Fix
threadgroup_rwsem <-> cpus_read_lock() deadlock") missed that
cpuset_attach() is also called from cgroup_attach_task_all().
Add cpus_read_lock() like what cgroup_procs_write_start() does.

Link: https://syzkaller.appspot.com/bug?extid=29d3a3b4d86c8136ad9e

 [1]
Reported-by: syzbot <syzbot+29d3a3b4d86c8136ad9e@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Fixes: 4f7e7236 ("cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock")
Signed-off-by: Tejun Heo <tj@kernel.org>

conflicts:
	kernel/cgroup/cgroup-internal.h
	kernel/cgroup/cgroup-v1.c
	kernel/cgroup/cgroup.c

Signed-off-by: Cai Xinchen <caixinchen1@huawei.com>
Reviewed-by: Wang Weiyang <wangweiyang2@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: Wang Weiyang <wangweiyang2@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>