linux-kernel - [PATCH 3/3] drm/sched: Add TODO entry for missing runqueue locks

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Message-ID: <20251017134716.187723-4-phasta@kernel.org>
Date: Fri, 17 Oct 2025 15:47:03 +0200
From: Philipp Stanner <phasta@...nel.org>
To: Matthew Brost <matthew.brost@...el.com>,
	Danilo Krummrich <dakr@...nel.org>,
	Philipp Stanner <phasta@...nel.org>,
	Christian König <ckoenig.leichtzumerken@...il.com>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Sumit Semwal <sumit.semwal@...aro.org>
Cc: dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org
Subject: [PATCH 3/3] drm/sched: Add TODO entry for missing runqueue locks

struct drm_sched_rq is not being locked at many places throughout the
scheduler, at least for readers. This was documented in a FIXME added
in:

commit 981b04d96856 ("drm/sched: improve docs around drm_sched_entity")

Add a TODO entry for that problem.

Signed-off-by: Philipp Stanner <phasta@...nel.org>
---
 drivers/gpu/drm/scheduler/TODO | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/gpu/drm/scheduler/TODO b/drivers/gpu/drm/scheduler/TODO
index 6a06e2858dd6..f4b5bee8e3eb 100644
--- a/drivers/gpu/drm/scheduler/TODO
+++ b/drivers/gpu/drm/scheduler/TODO
@@ -25,3 +25,16 @@
 	3. Port a driver as first user.
 	3. Document the new alternative in the docu of deprecated
 	   drm_sched_resubmit_jobs().
+
+* Unlocked readers for runqueues
+  - Difficulty: medium
+  - Contact: Philipp Stanner <phasta@...nel.org>
+  - Description:
+    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!).
+  - Tasks:
+	1. Check whether locks for runqueue readers can be added.
+	2. If yes, add the locks.
-- 
2.49.0