From: Wang Jiang <[email protected]>
Commit 9eb00b5f5697b ("drm/radeon: delete radeon_fence_process in
is_signaled, no deadlock") removed the hardware status check from
radeon_fence_is_signaled() to fix a self-deadlock caused by
wake_up_all(&rdev->fence_queue) being called with the fence queue
lock held.
However, removing the hardware poll entirely causes significant
performance regression (e.g. glxgears FPS drop) because the signaled
check becomes purely passive — it only reads the cached last_seq
without probing the GPU, so completed GPU work is not detected in
time, causing unnecessary CPU stalls in sync-heavy workloads.
Fix this by calling radeon_fence_read() directly in
radeon_fence_is_signaled() to poll the hardware fence counter
without updating last_seq or calling wake_up_all(). This restores
timely fence detection while avoiding the original deadlock, since
last_seq update and waiter wakeup remain solely in the interrupt
handler's responsibility.
Fixes: 9eb00b5f5697b ("drm/radeon: delete radeon_fence_process in is_signaled,
no deadlock")
Signed-off-by: Wang Jiang <[email protected]>
---
drivers/gpu/drm/radeon/radeon_fence.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/drivers/gpu/drm/radeon/radeon_fence.c
b/drivers/gpu/drm/radeon/radeon_fence.c
index 02a40e4750c7..047ec5a1d194 100644
--- a/drivers/gpu/drm/radeon/radeon_fence.c
+++ b/drivers/gpu/drm/radeon/radeon_fence.c
@@ -360,6 +360,18 @@ static bool radeon_fence_is_signaled(struct dma_fence *f)
if (atomic64_read(&rdev->fence_drv[ring].last_seq) >= seq)
return true;
+ /*
+ * Poll hardware directly without updating last_seq.
+ * This allows immediate detection of signaled fences (performance)
+ * while leaving last_seq update and wake_up_all() to the interrupt
+ * handler, avoiding:
+ * 1. Deadlock from calling wake_up_all() with fence lock held
+ * 2. Wake event stealing by advancing last_seq without waking waiters
+ * 3. rw_semaphore usage in atomic/irq context (unsafe on PREEMPT_RT)
+ */
+ if (radeon_fence_read(rdev, ring) >= (u32)seq)
+ return true;
+
return false;
}
--
2.25.1
