linux-kernel - Re: [PATCH] drm/msm/mdp4: Fix refcount leak in mdp4_modeset_init

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Date:   Fri, 10 Jun 2022 16:20:07 -0700
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Miaoqian Lin <linmq006@...il.com>, Rob Clark <robdclark@...il.com>,
        "Dmitry Baryshkov" <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, "David Airlie" <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Stephen Boyd <swboyd@...omium.org>,
        David Heidelberg <david@...t.cz>,
        Guo Zhengkui <guozhengkui@...o.com>,
        Xu Wang <vulab@...as.ac.cn>,
        Neil Armstrong <narmstrong@...libre.com>,
        Rob Herring <robh@...nel.org>, <linux-arm-msm@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm/mdp4: Fix refcount leak in mdp4_modeset_init_intf



On 6/7/2022 4:08 AM, Miaoqian Lin wrote:
> of_graph_get_remote_node() returns remote device node pointer with
> refcount incremented, we should use of_node_put() on it
> when not need anymore.
> Add missing of_node_put() to avoid refcount leak.
> 
> Fixes: 86418f90a4c1 ("drm: convert drivers to use of_graph_get_remote_node")
> Signed-off-by: Miaoqian Lin <linmq006@...il.com>
> ---
>   drivers/gpu/drm/msm/disp/mdp4/mdp4_kms.c | 2 ++
>   1 file changed, 2 insertions(+)
> 

This patch itself looks fine and will cover the cases when there was an 
error and we did not release the refcount.

But, even in the normal cases I am not finding where we are releasing 
the refcount for the panel_node.

I dont see a of_node_put() on mdp4_lcdc_encoder->panel_node.

Am i missing something?

> diff --git a/drivers/gpu/drm/msm/disp/mdp4/mdp4_kms.c b/drivers/gpu/drm/msm/disp/mdp4/mdp4_kms.c
> index fb48c8c19ec3..17cb1fc78379 100644
> --- a/drivers/gpu/drm/msm/disp/mdp4/mdp4_kms.c
> +++ b/drivers/gpu/drm/msm/disp/mdp4/mdp4_kms.c
> @@ -216,6 +216,7 @@ static int mdp4_modeset_init_intf(struct mdp4_kms *mdp4_kms,
>   		encoder = mdp4_lcdc_encoder_init(dev, panel_node);
>   		if (IS_ERR(encoder)) {
>   			DRM_DEV_ERROR(dev->dev, "failed to construct LCDC encoder\n");
> +			of_node_put(panel_node);
>   			return PTR_ERR(encoder);
>   		}
>   
> @@ -225,6 +226,7 @@ static int mdp4_modeset_init_intf(struct mdp4_kms *mdp4_kms,
>   		connector = mdp4_lvds_connector_init(dev, panel_node, encoder);
>   		if (IS_ERR(connector)) {
>   			DRM_DEV_ERROR(dev->dev, "failed to initialize LVDS connector\n");
> +			of_node_put(panel_node);
>   			return PTR_ERR(connector);
>   		}
>