[PATCH v2] drm/scheduler: Fix hang when sched_entity released

[Andrey Grodzovsky]

Problem: If scheduler is already stopped by the time sched_entity
is released and entity's job_queue not empty I encountred
a hang in drm_sched_entity_flush. This is because drm_sched_entity_is_idle
never becomes false.

Fix: In drm_sched_fini detach all sched_entities from the
scheduler's run queues. This will satisfy drm_sched_entity_is_idle.
Also wakeup all those processes stuck in sched_entity flushing
as the scheduler main thread which wakes them up is stopped by now.

v2:
Reverse order of drm_sched_rq_remove_entity and marking
s_entity as stopped to prevent reinserion back to rq due
to race.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
---
 drivers/gpu/drm/scheduler/sched_main.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 908b0b5..c6b7947 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -897,9 +897,40 @@ EXPORT_SYMBOL(drm_sched_init);
  */
 void drm_sched_fini(struct drm_gpu_scheduler *sched)
 {
+	int i;
+	struct drm_sched_entity *s_entity;
 	if (sched->thread)
 		kthread_stop(sched->thread);
 
+	/* Detach all sched_entites from this scheduler once it's stopped */
+	for (i = DRM_SCHED_PRIORITY_COUNT - 1; i >= DRM_SCHED_PRIORITY_MIN; i--) {
+		struct drm_sched_rq *rq = &sched->sched_rq[i];
+
+		if (!rq)
+			continue;
+
+		/* Loop this way because rq->lock is taken in drm_sched_rq_remove_entity */
+		spin_lock(&rq->lock);
+		while ((s_entity = list_first_entry_or_null(&rq->entities,
+							    struct drm_sched_entity,
+							    list))) {
+			spin_unlock(&rq->lock);
+
+			/* Prevent reinsertion and remove */
+			spin_lock(&s_entity->rq_lock);
+			s_entity->stopped = true;
+			drm_sched_rq_remove_entity(rq, s_entity);
+			spin_unlock(&s_entity->rq_lock);
+
+			spin_lock(&rq->lock);
+		}
+		spin_unlock(&rq->lock);
+
+	}
+
+	/* Wakeup everyone stuck in drm_sched_entity_flush for this scheduler */
+	wake_up_all(&sched->job_scheduled);
+
 	/* Confirm no work left behind accessing device structures */
 	cancel_delayed_work_sync(&sched->work_tdr);
 
-- 
2.7.4