Re: [PATCH v5 15/27] drm/scheduler: Fix hang when sched_entity released

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I need to take another look at this part when I don't have a massive headache any more.

Maybe split the patch set up into different parts, something like:
1. Adding general infrastructure.
2. Making sure all memory is unpolated.
3. Job and fence handling

Christian.

Am 28.04.21 um 17:11 schrieb 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.

v3:
Drop drm_sched_rq_remove_entity, only modify entity->stopped
and check for it in drm_sched_entity_is_idle

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@xxxxxxx>
Reviewed-by: Christian König <christian.koenig@xxxxxxx>
---
  drivers/gpu/drm/scheduler/sched_entity.c |  3 ++-
  drivers/gpu/drm/scheduler/sched_main.c   | 24 ++++++++++++++++++++++++
  2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index f0790e9471d1..cb58f692dad9 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -116,7 +116,8 @@ static bool drm_sched_entity_is_idle(struct drm_sched_entity *entity)
  	rmb(); /* for list_empty to work without lock */
if (list_empty(&entity->list) ||
-	    spsc_queue_count(&entity->job_queue) == 0)
+	    spsc_queue_count(&entity->job_queue) == 0 ||
+	    entity->stopped)
  		return true;
return false;
diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 908b0b56032d..ba087354d0a8 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -897,9 +897,33 @@ EXPORT_SYMBOL(drm_sched_init);
   */
  void drm_sched_fini(struct drm_gpu_scheduler *sched)
  {
+	struct drm_sched_entity *s_entity;
+	int i;
+
  	if (sched->thread)
  		kthread_stop(sched->thread);
+ 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;
+
+		spin_lock(&rq->lock);
+		list_for_each_entry(s_entity, &rq->entities, list)
+			/*
+			 * Prevents reinsertion and marks job_queue as idle,
+			 * it will removed from rq in drm_sched_entity_fini
+			 * eventually
+			 */
+			s_entity->stopped = true;
+		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);

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