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

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Message-ID: <c258b072-82cf-71a8-fdfb-79df52c5d480@quicinc.com>
Date:   Tue, 14 Jun 2022 09:31:15 -0700
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Miaoqian Lin <linmq006@...il.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 6/14/2022 3:09 AM, Dmitry Baryshkov wrote:
> 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.
> 

Alright, with that assurance,

Reviewed-by: Abhinav Kumar <quic_abhinavk@...cinc.com>

Will pick it up for -fixes.
>>
>>> 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);
>>>>            }
> 
>