Re: [PATCH v3] drm/scheduler: Fix hang when sched_entity released

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On 2021-02-26 3:04 a.m., Christian König wrote:


Am 25.02.21 um 22:37 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>
---
  drivers/gpu/drm/scheduler/sched_entity.c |  3 ++-
  drivers/gpu/drm/scheduler/sched_main.c   | 23 +++++++++++++++++++++++
  2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index 92d965b629c6..68b10813129a 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..b50fab472734 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -897,9 +897,32 @@ EXPORT_SYMBOL(drm_sched_init);
   */
  void drm_sched_fini(struct drm_gpu_scheduler *sched)
  {
+    int i;
+    struct drm_sched_entity *s_entity;

Please declare i last and have an empty line between declaration and code.

With that nit pick fixed the patch is Reviewed-by: Christian König <christian.koenig@xxxxxxx>. Going to push it to drm-misc-next.

Christian.


Done. Since you are pushing attaching the patch here.

Andrey



      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);

>From 7f0a1f4ee6d5fa24b50fee199e5d7ea316d2f08e Mon Sep 17 00:00:00 2001
From: Andrey Grodzovsky <andrey.grodzovsky@xxxxxxx>
Date: Fri, 12 Feb 2021 01:45:51 -0500
Subject: drm/scheduler: Fix hang when sched_entity released
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

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 92d965b629c6..68b10813129a 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);
 
-- 
2.25.1

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