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References: <20210517081601.1563193-1-yukuai3@huawei.com>
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From:   Robert Foss <robert.foss@linaro.org>
Date:   Mon, 17 May 2021 11:27:38 +0200
Message-ID: <CAG3jFyvjD+Gf5C+sWA8Qi9Hp-tJHeCjqbWX5Fds3m41nCLreyA@mail.gmail.com>
Subject: Re: [PATCH] drm: bridge: cdns-mhdp8546: Fix PM reference leak in cdns_mhdp_probe()
To:     Yu Kuai <yukuai3@huawei.com>
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
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Precedence: bulk

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");
>                 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