sched/fair: Avoid offline tasks starve to death for priority load balance

euleros inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I60S5R


CVE: NA

Reference: NA

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When priority load balance enabled for online/offline tasks co-location,
offline tasks maybe starve to death by load balance detach_tasks()
if env->loop exceed env->loop_max and can not be migrate to idle cpus.

So we should set env->loop to 0 and detach offline tasks again.

Fixes: fbfd4454 ("sched: Introduce priority load balance for CFS")

Signed-off-by: Song Zhang <zhangsong34@huawei.com>