Until a task's state has been seen as interruptible/uninterruptible
and it is no longer on_cpu, it is possible that the task may move
to another CPU (load balancing may cause this). Here is an example
where the race condition results in incorrect operation:
- cpu 0 calls put_prev_task on task A, task A's state is TASK_RUNNING
- cpu 0 runs task B, which attempts to wake up A
- cpu 0 begins try_to_wake_up(), recording src_cpu for task A as cpu 0
- cpu 1 then pulls task A (perhaps due to idle balance)
- cpu 1 runs task A, which then sleeps, becoming INTERRUPTIBLE
- cpu 0 continues in try_to_wake_up(), thinking task A's previous
cpu is 0, where it is actually 1
- if select_task_rq returns cpu 0, task A will be woken up on cpu 0
without properly updating its cpu to 0 in set_task_cpu()
CRs-Fixed: 665958
Change-Id: Icee004cb320bd8edfc772d9f74e670a9d4978a99
Signed-off-by: Steve Muckle <smuckle@codeaurora.org>
Steve Muckle
39414b4b9a