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@vger.kernel.org Fixes: 1ef7ed48356c ("drm/mediatek: Modify mediatek-drm for mt8195 multi mmsys support") Signed-off-by: Ma Ke make24@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) {
On Fri, 2025-07-18 at 11:32 +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.
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
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;
I've define label next_put_device_pdev_dev below, so
goto next_put_device_pdev_dev;
} 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;
I've define label next_put_device_drm_dev below, so
goto next_put_device_drm_dev;
} 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);
next_put_device_drm_dev:
put_device(drm_dev);
next_put_device_pdev_dev:
put_device(&pdev->dev);
+next:
next_put_node:
Regards, CK
of_node_put(node);
if (cnt == MAX_CRTC) break;
} } if (drm_priv->data->mmsys_dev_num == cnt) {
-- 2.25.1
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