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

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Message-ID: <0bdb3a64-e795-4aa0-86c9-efd7fc3d5a19@gmail.com>
Date:   Tue, 14 Jun 2022 18:07:05 +0800
From:   Miaoqian Lin <linmq006@...il.com>
To:     Abhinav Kumar <quic_abhinavk@...cinc.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

Hi, Abhinav

On 2022/6/11 7:20, Abhinav Kumar wrote:
>
>
> 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.
>
Thanks for your review.

I don't see it either. It's a bit messy because the reference assigned to mdp4_lcdc_encoder->panel_node and mdp4_lvds_connector->panel_node both.

> 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);
>>           }
>>