[PATCH v2 2/2] drm/todo: Add entry for unlocked drm/sched rq readers

Philipp Stanner
2025-11-07T13:57:25Z

Runqueues are currently almost everywhere being read unlocked in
drm/sched. At XDC 2025, the assembled developers were unsure whether
that's legal and whether it can be fixed. Someone should find out.

Add a todo entry for the unlocked runqueue reader problem.

Signed-off-by: Philipp Stanner <phasta@kernel.org>
---
Documentation/gpu/todo.rst | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
index 084e148e78c1..fc8bafd593d8 100644
--- a/Documentation/gpu/todo.rst
+++ b/Documentation/gpu/todo.rst
@@ -909,6 +909,20 @@ Contact: Christian König <ckoenig.leichtzumerken@gmail.com>

Level: Advanced

+Add locking for runqueues
+-------------------------
+
+There is an old FIXME by Sima in include/drm/gpu_scheduler.h. It details that
+struct drm_sched_rq is read at many places without any locks, not even with a
+READ_ONCE. At XDC 2025 no one could really tell why that is the case, whether
+locks are needed and whether they could be added. (But for real, that should
+probably be locked!). Check whether it's possible to add locks everywhere, and
+do so if yes.
+
+Contact: Philipp Stanner <phasta@kernel.org>
+
+Level: Intermediate
+
Outside DRM
===========

--
2.49.0