linux-kernel - [PATCH] drm/mediatek: Fix refcounting in mtk_drm_get_all_drm

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Message-Id: <20251003-mtk-drm-refcount-v1-1-3b3f2813b0db@collabora.com>
Date: Fri, 03 Oct 2025 10:08:28 +0200
From: Sjoerd Simons <sjoerd@...labora.com>
To: Chun-Kuang Hu <chunkuang.hu@...nel.org>, 
 Philipp Zabel <p.zabel@...gutronix.de>, David Airlie <airlied@...il.com>, 
 Simona Vetter <simona@...ll.ch>, Matthias Brugger <matthias.bgg@...il.com>, 
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
 CK Hu <ck.hu@...iatek.com>, Johan Hovold <johan@...nel.org>
Cc: dri-devel@...ts.freedesktop.org, linux-mediatek@...ts.infradead.org, 
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
 kernel@...labora.com, stable@...r.kernel.org, 
 Sjoerd Simons <sjoerd@...labora.com>
Subject: [PATCH] drm/mediatek: Fix refcounting in mtk_drm_get_all_drm_priv

dev_get_drvdata simply returns the driver data part of drm_dev, which
has its lifetime bound to the drm_dev. So only drop the reference in the
error paths, on success they will get dropped later.

Cc: stable@...r.kernel.org
Fixes: 9ba2556cef1df ("drm/mediatek: clean up driver data initialisation")
Signed-off-by: Sjoerd Simons <sjoerd@...labora.com>
---
 drivers/gpu/drm/mediatek/mtk_drm_drv.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
index 7841f59c52ee772dba3de416f410604f5f13eef2..c85fbecce9d6f0ade700e047e067ee7f9250f037 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
@@ -373,7 +373,7 @@ static int mtk_drm_match(struct device *dev, const void *data)
 static bool mtk_drm_get_all_drm_priv(struct device *dev)
 {
 	struct mtk_drm_private *drm_priv = dev_get_drvdata(dev);
-	struct mtk_drm_private *all_drm_priv[MAX_CRTC];
+	struct mtk_drm_private *all_drm_priv[MAX_CRTC] = { NULL, };
 	struct mtk_drm_private *temp_drm_priv;
 	struct device_node *phandle = dev->parent->of_node;
 	const struct of_device_id *of_id;
@@ -399,16 +399,22 @@ static bool mtk_drm_get_all_drm_priv(struct device *dev)
 			continue;
 
 		temp_drm_priv = dev_get_drvdata(drm_dev);
-		put_device(drm_dev);
-		if (!temp_drm_priv)
+		if (!temp_drm_priv) {
+			put_device(drm_dev);
 			continue;
+		}
 
-		if (temp_drm_priv->data->main_len)
+		if (temp_drm_priv->data->main_len) {
 			all_drm_priv[CRTC_MAIN] = temp_drm_priv;
-		else if (temp_drm_priv->data->ext_len)
+		} else if (temp_drm_priv->data->ext_len) {
 			all_drm_priv[CRTC_EXT] = temp_drm_priv;
-		else if (temp_drm_priv->data->third_len)
+		} else if (temp_drm_priv->data->third_len) {
 			all_drm_priv[CRTC_THIRD] = temp_drm_priv;
+		} else {
+			dev_warn(drm_dev, "Could not determine crtc type");
+			put_device(drm_dev);
+			continue;
+		}
 
 		if (temp_drm_priv->mtk_drm_bound)
 			cnt++;
@@ -427,6 +433,10 @@ static bool mtk_drm_get_all_drm_priv(struct device *dev)
 		return true;
 	}
 
+	for (i = 0; i < MAX_CRTC; i++)
+		if (all_drm_priv[i])
+			put_device(all_drm_priv[i]->dev);
+
 	return false;
 }
 

---
base-commit: 22b5e8cde1db67c64b83fc0e4e1ab166cacff246
change-id: 20251002-mtk-drm-refcount-e0f718d9364a

Best regards,
-- 
Sjoerd Simons <sjoerd@...labora.com>