sched: Fix offline task can't be killed in a timely

hulk inclusion
category: bugfix
bugzilla: 51828, https://gitee.com/openeuler/kernel/issues/I4K96G


CVE: NA

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

If online tasks occupy 100% CPU resources, offline tasks can't be scheduled
since offline tasks are throttled, as a result, offline task can't timely
respond after receiving SIGKILL signal.

Signed-off-by: Zheng Zucheng <zhengzucheng@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: Chen Hui <judy.chenhui@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>