drm/scheduler: fix last_scheduled handling

Make sure we access last_scheduled only after checking that there are no
more jobs on the entity.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Nayan Deshmukh <nayan26deshmukh@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/scheduler/gpu_scheduler.c

@@ -565,20 +565,21 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job,
 			       struct drm_sched_entity *entity)
 {
 	struct drm_sched_rq *rq = entity->rq;
-	bool first, reschedule, idle;
+	bool first;
 
-	idle = entity->last_scheduled == NULL ||
-		dma_fence_is_signaled(entity->last_scheduled);
 	first = spsc_queue_count(&entity->job_queue) == 0;
-	reschedule = idle && first && (entity->num_rq_list > 1);
+	if (first && (entity->num_rq_list > 1)) {
+		struct dma_fence *fence;
 
-	if (reschedule) {
+		fence = READ_ONCE(entity->last_scheduled);
+		if (fence == NULL || dma_fence_is_signaled(fence)) {
 			rq = drm_sched_entity_get_free_sched(entity);
 			spin_lock(&entity->rq_lock);
 			drm_sched_rq_remove_entity(entity->rq, entity);
 			entity->rq = rq;
 			spin_unlock(&entity->rq_lock);
 		}
+	}
 
 	sched_job->sched = entity->rq->sched;
 	sched_job->s_fence->sched = entity->rq->sched;