linux-kernel - Re: [PATCH] drm: bridge: cdns-mhdp8546: Fix PM reference leak in cdns_mhdp

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Date:   Mon, 17 May 2021 20:34:20 +0800
From:   "yukuai (C)" <yukuai3@...wei.com>
To:     Robert Foss <robert.foss@...aro.org>
CC:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        <yi.zhang@...wei.com>
Subject: Re: [PATCH] drm: bridge: cdns-mhdp8546: Fix PM reference leak in
 cdns_mhdp_probe()

On 2021/05/17 17:27, Robert Foss wrote:
> Hey Yu,
> 
> On Mon, 17 May 2021 at 10:08, Yu Kuai <yukuai3@...wei.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@...wei.com>
>> Signed-off-by: Yu Kuai <yukuai3@...wei.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");
>>                  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].
> 
> [1] https://elixir.bootlin.com/linux/latest/source/include/linux/pm_runtime.h#L384
> [2] https://elixir.bootlin.com/linux/latest/source/drivers/base/power/runtime.c#L1383
> .
> 
Hi,

Thank you very much for your explanation

Yu Kuai