[PATCH v2] drm/sched: Remove optimization that causes hang when killing dependent jobs

[Lin . Cao]

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: sta...@vger.kernel.org # v4.6+

Signed-off-by: Lin.Cao <linca...@amd.com>
Reviewed-by: Christian König <christian.koe...@amd.com>
---
 drivers/gpu/drm/scheduler/sched_entity.c | 21 ++-------------------
 1 file changed, 2 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c 
b/drivers/gpu/drm/scheduler/sched_entity.c
index e671aa241720..ac678de7fe5e 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -355,17 +355,6 @@ 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_wakeup - callback to clear the entity's dependency and
  * wake up the scheduler
@@ -376,7 +365,8 @@ 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);
 }
 
@@ -429,13 +419,6 @@ 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,
-- 
2.46.1