[PATCH 1/2] drm/sched: Do not restore unsaved virtual runtime

Prevent pushing a new job to an entity seeing it being the first in the
queue, and hence entering the drm_sched_rq_add_entity() path, if the pop
side in drm_sched_entity_pop_job() has de-queued the job but not yet
updated the saved virtual time.

We do this by pulling the locked sections out to encompass both the queue
push/pop and corresponding rbtree management.

Signed-off-by: Tvrtko Ursulin <[email protected]>
Fixes: 2fa4d8e2c109 ("drm/sched: Add fair scheduling policy")
Suggested-by: [email protected] # via Claude Opus
Tested-by: [email protected]
Cc: Christian König <[email protected]>
Cc: Danilo Krummrich <[email protected]>
Cc: Philipp Stanner <[email protected]>
Cc: Pierre-Eric Pelloux-Prayer <[email protected]>
Cc: Matthew Brost <[email protected]>
Cc: Vitaly Prosyak <[email protected]>
---
 drivers/gpu/drm/scheduler/sched_entity.c |  8 +++++++-
 drivers/gpu/drm/scheduler/sched_rq.c     | 20 +++++++++-----------
 2 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index a4a7efdbf229..673ca9cbf362 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -559,9 +559,10 @@ struct drm_sched_job *drm_sched_entity_pop_job(struct drm_sched_entity *entity)
 	 */
 	smp_wmb();
 
+	spin_lock(&entity->lock);
 	spsc_queue_pop(&entity->job_queue);
-
 	drm_sched_rq_pop_entity(entity);
+	spin_unlock(&entity->lock);
 
 	/* Jobs and entities might have different lifecycles. Since we're
 	 * removing the job from the entities queue, set the jobs entity pointer
@@ -647,6 +648,9 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
 	 * Make sure to set the submit_ts first, to avoid a race.
 	 */
 	sched_job->submit_ts = submit_ts = ktime_get();
+
+	spin_lock(&entity->lock);
+
 	first = spsc_queue_push(&entity->job_queue, &sched_job->queue_node);
 
 	/* first job wakes up scheduler */
@@ -657,5 +661,7 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
 		if (sched)
 			drm_sched_wakeup(sched);
 	}
+
+	spin_unlock(&entity->lock);
 }
 EXPORT_SYMBOL(drm_sched_entity_push_job);
diff --git a/drivers/gpu/drm/scheduler/sched_rq.c b/drivers/gpu/drm/scheduler/sched_rq.c
index 0464d324d98d..23f46ec610e7 100644
--- a/drivers/gpu/drm/scheduler/sched_rq.c
+++ b/drivers/gpu/drm/scheduler/sched_rq.c
@@ -257,19 +257,17 @@ static ktime_t drm_sched_entity_get_job_ts(struct drm_sched_entity *entity)
 struct drm_gpu_scheduler *
 drm_sched_rq_add_entity(struct drm_sched_entity *entity, ktime_t ts)
 {
+	struct drm_sched_rq *rq = entity->rq;
 	struct drm_gpu_scheduler *sched;
-	struct drm_sched_rq *rq;
 
 	/* Add the entity to the run queue */
-	spin_lock(&entity->lock);
+	lockdep_assert_held(&entity->lock);
+
 	if (entity->stopped) {
-		spin_unlock(&entity->lock);
-
 		DRM_ERROR("Trying to push to a killed entity\n");
 		return NULL;
 	}
 
-	rq = entity->rq;
 	spin_lock(&rq->lock);
 	sched = rq->sched;
 
@@ -289,7 +287,6 @@ drm_sched_rq_add_entity(struct drm_sched_entity *entity, ktime_t ts)
 	drm_sched_rq_update_fifo_locked(entity, rq, ts);
 
 	spin_unlock(&rq->lock);
-	spin_unlock(&entity->lock);
 
 	return sched;
 }
@@ -343,16 +340,17 @@ drm_sched_rq_next_rr_ts(struct drm_sched_rq *rq,
  */
 void drm_sched_rq_pop_entity(struct drm_sched_entity *entity)
 {
+	struct drm_sched_rq *rq = entity->rq;
 	struct drm_sched_job *next_job;
-	struct drm_sched_rq *rq;
+
+	lockdep_assert_held(&entity->lock);
+
+	spin_lock(&rq->lock);
 
 	/*
 	 * Update the entity's location in the min heap according to
 	 * the timestamp of the next job, if any.
 	 */
-	spin_lock(&entity->lock);
-	rq = entity->rq;
-	spin_lock(&rq->lock);
 	next_job = drm_sched_entity_queue_peek(entity);
 	if (next_job) {
 		ktime_t ts;
@@ -375,8 +373,8 @@ void drm_sched_rq_pop_entity(struct drm_sched_entity *entity)
 			drm_sched_entity_save_vruntime(entity, min_vruntime);
 		}
 	}
+
 	spin_unlock(&rq->lock);
-	spin_unlock(&entity->lock);
 }
 
 /**
-- 
2.54.0