diff options
| -rw-r--r-- | kernel/sched.c | 69 |
1 files changed, 60 insertions, 9 deletions
diff --git a/kernel/sched.c b/kernel/sched.c index 49be34e..a747591 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -1159,21 +1159,72 @@ void wait_task_inactive(struct task_struct *p) { unsigned long flags; struct rq *rq; - int preempted; + struct prio_array *array; + int running; repeat: + /* + * We do the initial early heuristics without holding + * any task-queue locks at all. We'll only try to get + * the runqueue lock when things look like they will + * work out! + */ + rq = task_rq(p); + + /* + * If the task is actively running on another CPU + * still, just relax and busy-wait without holding + * any locks. + * + * NOTE! Since we don't hold any locks, it's not + * even sure that "rq" stays as the right runqueue! + * But we don't care, since "task_running()" will + * return false if the runqueue has changed and p + * is actually now running somewhere else! + */ + while (task_running(rq, p)) + cpu_relax(); + + /* + * Ok, time to look more closely! We need the rq + * lock now, to be *sure*. If we're wrong, we'll + * just go back and repeat. + */ rq = task_rq_lock(p, &flags); - /* Must be off runqueue entirely, not preempted. */ - if (unlikely(p->array || task_running(rq, p))) { - /* If it's preempted, we yield. It could be a while. */ - preempted = !task_running(rq, p); - task_rq_unlock(rq, &flags); + running = task_running(rq, p); + array = p->array; + task_rq_unlock(rq, &flags); + + /* + * Was it really running after all now that we + * checked with the proper locks actually held? + * + * Oops. Go back and try again.. + */ + if (unlikely(running)) { cpu_relax(); - if (preempted) - yield(); goto repeat; } - task_rq_unlock(rq, &flags); + + /* + * It's not enough that it's not actively running, + * it must be off the runqueue _entirely_, and not + * preempted! + * + * So if it wa still runnable (but just not actively + * running right now), it's preempted, and we should + * yield - it could be a while. + */ + if (unlikely(array)) { + yield(); + goto repeat; + } + + /* + * Ahh, all good. It wasn't running, and it wasn't + * runnable, which means that it will never become + * running in the future either. We're all done! + */ } /*** |
