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-rw-r--r--kernel/sched.c29
1 files changed, 27 insertions, 2 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index fde1a10..0236958 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1867,16 +1867,24 @@ migrate_task(struct task_struct *p, int dest_cpu, struct migration_req *req)
/*
* wait_task_inactive - wait for a thread to unschedule.
*
+ * If @match_state is nonzero, it's the @p->state value just checked and
+ * not expected to change. If it changes, i.e. @p might have woken up,
+ * then return zero. When we succeed in waiting for @p to be off its CPU,
+ * we return a positive number (its total switch count). If a second call
+ * a short while later returns the same number, the caller can be sure that
+ * @p has remained unscheduled the whole time.
+ *
* The caller must ensure that the task *will* unschedule sometime soon,
* else this function might spin for a *long* time. This function can't
* be called with interrupts off, or it may introduce deadlock with
* smp_call_function() if an IPI is sent by the same process we are
* waiting to become inactive.
*/
-void wait_task_inactive(struct task_struct *p)
+unsigned long wait_task_inactive(struct task_struct *p, long match_state)
{
unsigned long flags;
int running, on_rq;
+ unsigned long ncsw;
struct rq *rq;
for (;;) {
@@ -1899,8 +1907,11 @@ void wait_task_inactive(struct task_struct *p)
* return false if the runqueue has changed and p
* is actually now running somewhere else!
*/
- while (task_running(rq, p))
+ while (task_running(rq, p)) {
+ if (match_state && unlikely(p->state != match_state))
+ return 0;
cpu_relax();
+ }
/*
* Ok, time to look more closely! We need the rq
@@ -1910,9 +1921,21 @@ void wait_task_inactive(struct task_struct *p)
rq = task_rq_lock(p, &flags);
running = task_running(rq, p);
on_rq = p->se.on_rq;
+ ncsw = 0;
+ if (!match_state || p->state == match_state) {
+ ncsw = p->nivcsw + p->nvcsw;
+ if (unlikely(!ncsw))
+ ncsw = 1;
+ }
task_rq_unlock(rq, &flags);
/*
+ * If it changed from the expected state, bail out now.
+ */
+ if (unlikely(!ncsw))
+ break;
+
+ /*
* Was it really running after all now that we
* checked with the proper locks actually held?
*
@@ -1944,6 +1967,8 @@ void wait_task_inactive(struct task_struct *p)
*/
break;
}
+
+ return ncsw;
}
/***
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