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

[Christian König]

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 at amd.com>
> ---
>   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 at amd.com>. Going to push it to drm-misc-next.

Christian.

>   	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);
>