[PATCH 2/2] drm/sched: document the RCU dependency

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Tvrkos patches added RCU protection to the returned strings from
get_timeline_name()/get_driver_name() callbacks of the dma_fence
backends.

This fixed use after free problems for a couple of drivers, but we never
documented the consequences for the drm_sched_fence.

Add a few words on the function documentation to note that we need an
RCU grace period between signaling the last scheduler fence and
scheduler teardown.

Signed-off-by: Christian König <christian.koenig@amd.com>
---
 drivers/gpu/drm/scheduler/sched_main.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 6cb6f9546493..22103cb07782 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -1203,6 +1203,10 @@ static void drm_sched_cancel_remaining_jobs(struct drm_gpu_scheduler *sched)
  * is implemented, all jobs will be canceled through it and afterwards cleaned
  * up through &struct drm_sched_backend_ops.free_job. If cancel_job is not
  * implemented, memory could leak.
+ *
+ * The scheduler fences timeline name is returned protected by the signaled
+ * status and RCU, so an RCU grace period is necessary between signaling the
+ * last scheduler fence and tearing down the scheduler who originated it.
  */
 void drm_sched_fini(struct drm_gpu_scheduler *sched)
 {
-- 
2.43.0