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 <[email protected]>
Reviewed-by: Boris Brezillon <[email protected]>
Reviewed-by: Liviu Dudau <[email protected]>
Reviewed-by: Steven Price <[email protected]>

---
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

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