On Tue, 2025-08-12 at 15:19 +0800, Ma Ke wrote:

External email : Please do not click links or open attachments until you have verified the sender or the content.

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.

Reviewed-by: CK Hu ck.hu@mediatek.com

Cc: stable@vger.kernel.org Fixes: 1ef7ed48356c ("drm/mediatek: Modify mediatek-drm for mt8195 multi mmsys support") Signed-off-by: Ma Ke make24@iscas.ac.cn

---

Changes in v2:

• added goto labels as suggestions.

---

drivers/gpu/drm/mediatek/mtk_drm_drv.c | 21 ++++++++++++++------- 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c index d5e6bab36414..f8a817689e16 100644 --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c @@ -387,19 +387,19 @@ 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_put_node;
  
            pdev = of_find_device_by_node(node);
            if (!pdev)
  

•                   continue;
  

•                   goto next_put_node;
  
            drm_dev = device_find_child(&pdev->dev, NULL, mtk_drm_match);
            if (!drm_dev)
  

•                   continue;
  

•                   goto next_put_device_pdev_dev;
  
            temp_drm_priv = dev_get_drvdata(drm_dev);
            if (!temp_drm_priv)
  

•                   continue;
  

•                   goto next_put_device_drm_dev;
  
            if (temp_drm_priv->data->main_len)
                    all_drm_priv[CRTC_MAIN] = temp_drm_priv;
  

@@ -411,10 +411,17 @@ 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);
  

+next_put_device_drm_dev:

•           put_device(drm_dev);
  

+next_put_device_pdev_dev:

•           put_device(&pdev->dev);
  

+next_put_node:

•           of_node_put(node);
  

•           if (cnt == MAX_CRTC)
                    break;
  

•           }
    }
  
    if (drm_priv->data->mmsys_dev_num == cnt) {
  

-- 2.25.1