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-rw-r--r--kernel/sched.c69
1 files changed, 60 insertions, 9 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 49be34e1f0b..a7475913b00 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!
+ */
}
/***