[PATCH 5.15.y] drm/sched: Remove optimization that causes hang when killing dependent jobs

[Sasha Levin <sashal@kernel.org>]

From: "Lin.Cao" <lincao12@amd.com>

[ Upstream commit 15f77764e90a713ee3916ca424757688e4f565b9 ]

When application A submits jobs and application B submits a job with a
dependency on A's fence, the normal flow wakes up the scheduler after
processing each job. However, the optimization in
drm_sched_entity_add_dependency_cb() uses a callback that only clears
dependencies without waking up the scheduler.

When application A is killed before its jobs can run, the callback gets
triggered but only clears the dependency without waking up the scheduler,
causing the scheduler to enter sleep state and application B to hang.

Remove the optimization by deleting drm_sched_entity_clear_dep() and its
usage, ensuring the scheduler is always woken up when dependencies are
cleared.

Fixes: 777dbd458c89 ("drm/amdgpu: drop a dummy wakeup scheduler")
Cc: stable@vger.kernel.org # v4.6+
Signed-off-by: Lin.Cao <lincao12@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://lore.kernel.org/r/20250717084453.921097-1-lincao12@amd.com
[ Changed drm_sched_wakeup_if_can_queue() calls to drm_sched_wakeup() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/scheduler/sched_entity.c | 27 ++++--------------------
 1 file changed, 4 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index 049d520226b1..9343b5a74c71 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -317,21 +317,8 @@ void drm_sched_entity_destroy(struct drm_sched_entity *entity)
 EXPORT_SYMBOL(drm_sched_entity_destroy);
 
 /*
- * drm_sched_entity_clear_dep - callback to clear the entities dependency
- */
-static void drm_sched_entity_clear_dep(struct dma_fence *f,
-				       struct dma_fence_cb *cb)
-{
-	struct drm_sched_entity *entity =
-		container_of(cb, struct drm_sched_entity, cb);
-
-	entity->dependency = NULL;
-	dma_fence_put(f);
-}
-
-/*
- * drm_sched_entity_clear_dep - callback to clear the entities dependency and
- * wake up scheduler
+ * drm_sched_entity_wakeup - callback to clear the entity's dependency and
+ * wake up the scheduler
  */
 static void drm_sched_entity_wakeup(struct dma_fence *f,
 				    struct dma_fence_cb *cb)
@@ -339,7 +326,8 @@ static void drm_sched_entity_wakeup(struct dma_fence *f,
 	struct drm_sched_entity *entity =
 		container_of(cb, struct drm_sched_entity, cb);
 
-	drm_sched_entity_clear_dep(f, cb);
+	entity->dependency = NULL;
+	dma_fence_put(f);
 	drm_sched_wakeup(entity->rq->sched);
 }
 
@@ -395,13 +383,6 @@ static bool drm_sched_entity_add_dependency_cb(struct drm_sched_entity *entity)
 		fence = dma_fence_get(&s_fence->scheduled);
 		dma_fence_put(entity->dependency);
 		entity->dependency = fence;
-		if (!dma_fence_add_callback(fence, &entity->cb,
-					    drm_sched_entity_clear_dep))
-			return true;
-
-		/* Ignore it when it is already scheduled */
-		dma_fence_put(fence);
-		return false;
 	}
 
 	if (!dma_fence_add_callback(entity->dependency, &entity->cb,
-- 
2.39.5