[PATCH v3] drm/sched: Wake up scheduler when killing jobs to prevent hang

[Lin.Cao]

When application A submits jobs (a1, a2, a3) and application B submits
job b1 with a dependency on a2's scheduler fence, the normal execution
flow is:
1. a1 gets popped from the entity by the scheduler
2. run_job(a1) executes
3. a1's scheduled fence gets signaled
4. drm_sched_run_job_work() calls drm_sched_run_job_queue() at the end
5. The scheduler wakes up and re-selects entities to pop jobs
6. Since b1's dependency is cleared, scheduler can select b1 and continue

However, if application A is killed before a1 gets popped by the scheduler,
then a1, a2, a3 are killed sequentially by drm_sched_entity_kill_jobs_cb().
During the kill process, their scheduled fences are still signaled, but
the kill process itself lacks the work_run_job that would normally be
scheduled by drm_sched_run_job_work(). This means b1's dependency gets
cleared, but there's no work_run_job to drive the scheduler to continue
running, causing the scheduler to enter sleep state and application B to hang.

Add drm_sched_wakeup() in entity_kill_job_work() to prevent scheduler
sleep and subsequent application hangs.

v2:
- Move drm_sched_wakeup() to after drm_sched_fence_scheduled()

v3:
- Clarify the normal flow vs kill process comparison

Signed-off-by: Lin.Cao <lincao12 at amd.com>
---
 drivers/gpu/drm/scheduler/sched_entity.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index e671aa241720..66f2a43c58fd 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -177,6 +177,7 @@ static void drm_sched_entity_kill_jobs_work(struct work_struct *wrk)
 	struct drm_sched_job *job = container_of(wrk, typeof(*job), work);
 
 	drm_sched_fence_scheduled(job->s_fence, NULL);
+	drm_sched_wakeup(job->sched);
 	drm_sched_fence_finished(job->s_fence, -ESRCH);
 	WARN_ON(job->s_fence->parent);
 	job->sched->ops->free_job(job);
-- 
2.46.1