[PATCH] drm/mediatek: Fix device/node reference count leaks in mtk_drm_get_all_drm_priv

[Ma Ke]

Using device_find_child() and of_find_device_by_node() to locate
devices could cause an imbalance in the device's reference count.
device_find_child() and of_find_device_by_node() both call
get_device() to increment the reference count of the found device
before returning the pointer. In mtk_drm_get_all_drm_priv(), these
references are never released through put_device(), resulting in
permanent reference count increments. Additionally, the
for_each_child_of_node() iterator fails to release node references in
all code paths. This leaks device node references when loop
termination occurs before reaching MAX_CRTC. These reference count
leaks may prevent device/node resources from being properly released
during driver unbind operations.

As comment of device_find_child() says, 'NOTE: you will need to drop
the reference with put_device() after use'.

Found by code review.

Cc: stable at vger.kernel.org
Fixes: 1ef7ed48356c ("drm/mediatek: Modify mediatek-drm for mt8195 multi mmsys support")
Signed-off-by: Ma Ke <make24 at iscas.ac.cn>
---
 drivers/gpu/drm/mediatek/mtk_drm_drv.c | 27 +++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
index 7c0c12dde488..c78186debd3e 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
@@ -388,19 +388,24 @@ static bool mtk_drm_get_all_drm_priv(struct device *dev)
 
 		of_id = of_match_node(mtk_drm_of_ids, node);
 		if (!of_id)
-			continue;
+			goto next;
 
 		pdev = of_find_device_by_node(node);
 		if (!pdev)
-			continue;
+			goto next;
 
 		drm_dev = device_find_child(&pdev->dev, NULL, mtk_drm_match);
-		if (!drm_dev)
-			continue;
+		if (!drm_dev) {
+			put_device(&pdev->dev);
+			goto next;
+		}
 
 		temp_drm_priv = dev_get_drvdata(drm_dev);
-		if (!temp_drm_priv)
-			continue;
+		if (!temp_drm_priv) {
+			put_device(drm_dev);
+			put_device(&pdev->dev);
+			goto next;
+		}
 
 		if (temp_drm_priv->data->main_len)
 			all_drm_priv[CRTC_MAIN] = temp_drm_priv;
@@ -412,10 +417,14 @@ static bool mtk_drm_get_all_drm_priv(struct device *dev)
 		if (temp_drm_priv->mtk_drm_bound)
 			cnt++;
 
-		if (cnt == MAX_CRTC) {
-			of_node_put(node);
+		put_device(drm_dev);
+		put_device(&pdev->dev);
+
+next:
+		of_node_put(node);
+
+		if (cnt == MAX_CRTC)
 			break;
-		}
 	}
 
 	if (drm_priv->data->mmsys_dev_num == cnt) {
-- 
2.25.1