linux-kernel - [PATCH 2/2] drm/todo: Add entry for unlocked drm/sched rq readers

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Message-ID: <20251031120014.248416-4-phasta@kernel.org>
Date: Fri, 31 Oct 2025 13:00:15 +0100
From: Philipp Stanner <phasta@...nel.org>
To: David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Jonathan Corbet <corbet@....net>
Cc: dri-devel@...ts.freedesktop.org,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Philipp Stanner <phasta@...nel.org>
Subject: [PATCH 2/2] drm/todo: Add entry for unlocked drm/sched rq readers

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@...nel.org>
---
 Documentation/gpu/todo.rst | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
index 835e799ddfe2..7d7e9e3741e9 100644
--- a/Documentation/gpu/todo.rst
+++ b/Documentation/gpu/todo.rst
@@ -909,6 +909,20 @@ Contact: Christian König <ckoenig.leichtzumerken@...il.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@...nel.org>
+
+Level: Intermediate
+
 Outside DRM
 ===========
 
-- 
2.49.0