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

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Date:   Tue, 14 Jun 2022 13:09:13 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Miaoqian Lin <linmq006@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Rob Clark <robdclark@...il.com>, 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 14/06/2022 13:07, Miaoqian Lin wrote:
> 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.

I have a plan to rework mdp4 lcdc support once I get my ifc6410 lvds 
cable. Thus I think we can land this patch now and fix the mdp4 
lcdc/lvds code leaking the reference in the due time.

> 
>> 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);
>>>            }
>>>    


-- 
With best wishes
Dmitry