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Subject: Re: [PATCH] drm: bridge: cdns-mhdp8546: Fix PM reference leak in
 cdns_mhdp_probe()
To:     Robert Foss <robert.foss@linaro.org>,
        Johan Hovold <johan@kernel.org>
CC:     Andrzej Hajda <a.hajda@samsung.com>,
        Neil Armstrong <narmstrong@baylibre.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        <yi.zhang@huawei.com>
References: <20210517081601.1563193-1-yukuai3@huawei.com>
 <CAG3jFyvjD+Gf5C+sWA8Qi9Hp-tJHeCjqbWX5Fds3m41nCLreyA@mail.gmail.com>
 <YKNv5fsVaTrslJZw@hovoldconsulting.com>
 <CAG3jFyu9x0NERFQ78GAX_6TUimB_PmBXkcVJZ9i+HXbK=N0dmQ@mail.gmail.com>
From:   "yukuai (C)" <yukuai3@huawei.com>
Message-ID: <da560b11-4ee0-c534-6dd0-4e080a1e10f3@huawei.com>
Date:   Sat, 29 May 2021 17:15:20 +0800
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ping ...

On 2021/05/18 20:58, Robert Foss wrote:
> On Tue, 18 May 2021 at 09:42, Johan Hovold <johan@kernel.org> wrote:
>>
>> On Mon, May 17, 2021 at 11:27:38AM +0200, Robert Foss wrote:
>>> Hey Yu,
>>>
>>> On Mon, 17 May 2021 at 10:08, Yu Kuai <yukuai3@huawei.com> wrote:
>>>>
>>>> pm_runtime_get_sync will increment pm usage counter even it failed.
>>>> Forgetting to putting operation will result in reference leak here.
>>>> Fix it by replacing it with pm_runtime_resume_and_get to keep usage
>>>> counter balanced.
>>>>
>>>> Reported-by: Hulk Robot <hulkci@huawei.com>
>>>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>>>> ---
>>>>   drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c | 2 +-
>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
>>>> index 0cd8f40fb690..305489d48c16 100644
>>>> --- a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
>>>> +++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
>>>> @@ -2478,7 +2478,7 @@ static int cdns_mhdp_probe(struct platform_device *pdev)
>>>>          clk_prepare_enable(clk);
>>>>
>>>>          pm_runtime_enable(dev);
>>>> -       ret = pm_runtime_get_sync(dev);
>>>> +       ret = pm_runtime_resume_and_get(dev);
>>>>          if (ret < 0) {
>>>>                  dev_err(dev, "pm_runtime_get_sync failed\n");
> 
> This error message is a bit confusing now, could you update it.
> 
>>>>                  pm_runtime_disable(dev);
>>>
>>> The code is correct as it is. If pm_runtime_get_sync() fails and
>>> increments[1] the pm.usage_count variable, that isn't a problem since
>>> pm_runtime_disable() disables pm, and resets pm.usage_count variable
>>> to zero[2].
>>
>> No it doesn't; pm_runtime_disable() does not reset the counter and you
>> still need to decrement the usage count when pm_runtime_get_sync()
>> fails.
> 
> Thanks for chiming in Johan, you're absolutely right and I must have
> misread something.
> 
> With the above fix, feel free to add my r-b.
> 
> Reviewed-by: Robert Foss <robert.foss@linaro.org>
> .
>