From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	=?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@amd.com>,
	Wang Jiang <jiangwang@kylinos.cn>,
	Alex Deucher <alexander.deucher@amd.com>
Subject: [PATCH 7.1 031/228] drm/radeon: restore hardware polling in fence_is_signaled to fix performance regression
Date: Thu, 20 Aug 2026 16:52:53 +0200
Message-ID: <20260820145245.406990482@linuxfoundation.org>
In-Reply-To: <20260820145244.450574346@linuxfoundation.org>
References: <20260820145244.450574346@linuxfoundation.org>
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7.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Wang Jiang <jiangwang@kylinos.cn>

commit 5f08eee9c3fb1a5a70966612e0ff249900f8e77b upstream.

Commit 527ba26e50ec ("drm/radeon: delete radeon_fence_process in
is_signaled, no deadlock") removed the hardware polling 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 polling entirely causes significant performance
regression (e.g. glxgears FPS drop) because the fence 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_activity() directly instead of
radeon_fence_process(). radeon_fence_activity() reads the hardware
fence counter and updates last_seq via atomic ops without calling
wake_up_all(), thus avoiding the deadlock while restoring timely
fence detection.

Fixes: 527ba26e50ec ("drm/radeon: delete radeon_fence_process in is_signaled, no deadlock")
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Wang Jiang <jiangwang@kylinos.cn>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit f59ad4cca219c7fdf934f712c5860ec5f5900fd7)
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/gpu/drm/radeon/radeon_fence.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/gpu/drm/radeon/radeon_fence.c
+++ b/drivers/gpu/drm/radeon/radeon_fence.c
@@ -360,6 +360,13 @@ static bool radeon_fence_is_signaled(str
 	if (atomic64_read(&rdev->fence_drv[ring].last_seq) >= seq)
 		return true;
 
+	if (down_read_trylock(&rdev->exclusive_lock)) {
+		radeon_fence_activity(rdev, ring);
+		up_read(&rdev->exclusive_lock);
+
+		if (atomic64_read(&rdev->fence_drv[ring].last_seq) >= seq)
+			return true;
+	}
 	return false;
 }