linux-kernel - [PATCH v2] drm/panthor: fix for dma-fence safe access rules

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Message-ID: <20251204174545.399059-1-olvaffe@gmail.com>
Date: Thu,  4 Dec 2025 09:45:45 -0800
From: Chia-I Wu <olvaffe@...il.com>
To: Boris Brezillon <boris.brezillon@...labora.com>,
	Steven Price <steven.price@....com>,
	Liviu Dudau <liviu.dudau@....com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Grant Likely <grant.likely@...aro.org>,
	Heiko Stuebner <heiko@...ech.de>,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	tvrtko.ursulin@...lia.com
Subject: [PATCH v2] drm/panthor: fix for dma-fence safe access rules

Commit 506aa8b02a8d6 ("dma-fence: Add safe access helpers and document
the rules") details the dma-fence safe access rules. The most common
culprit is that drm_sched_fence_get_timeline_name may race with
group_free_queue.

Signed-off-by: Chia-I Wu <olvaffe@...il.com>
Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>
Reviewed-by: Liviu Dudau <liviu.dudau@....com>
Reviewed-by: Steven Price <steven.price@....com>

---
v2: collect R-bs and drop misleading Fixes: tag
---
 drivers/gpu/drm/panthor/panthor_sched.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
index 33b9ef537e359..a8b1347e4da71 100644
--- a/drivers/gpu/drm/panthor/panthor_sched.c
+++ b/drivers/gpu/drm/panthor/panthor_sched.c
@@ -23,6 +23,7 @@
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
+#include <linux/rcupdate.h>
 
 #include "panthor_devfreq.h"
 #include "panthor_device.h"
@@ -923,6 +924,9 @@ static void group_release_work(struct work_struct *work)
 						   release_work);
 	u32 i;
 
+	/* dma-fences may still be accessing group->queues under rcu lock. */
+	synchronize_rcu();
+
 	for (i = 0; i < group->queue_count; i++)
 		group_free_queue(group, group->queues[i]);
 
-- 
2.52.0.223.gf5cc29aaa4-goog