Revert "sched/fair: Make sure to try to detach at least one movable task"

In the Linux kernel, the following vulnerability has been resolved:

Revert "sched/fair: Make sure to try to detach at least one movable task"

This reverts commit b0defa7ae03ecf91b8bfd10ede430cff12fcbd06.

b0defa7ae03ec changed the load balancing logic to ignore env.max_loop if

all tasks examined to that point were pinned. The goal of the patch was

to make it more likely to be able to detach a task buried in a long list

of pinned tasks. However, this has the unfortunate side effect of

creating an O(n) iteration in detach_tasks(), as we now must fully

iterate every task on a cpu if all or most are pinned. Since this load

balance code is done with rq lock held, and often in softirq context, it

is very easy to trigger hard lockups. We observed such hard lockups with

a user who affined O(10k) threads to a single cpu.

When I discussed this with Vincent he initially suggested that we keep

the limit on the number of tasks to detach, but increase the number of

tasks we can search. However, after some back and forth on the mailing

list, he recommended we instead revert the original patch, as it seems

likely no one was actually getting hit by the original issue.