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

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Message-ID: <CAG3jFyu9x0NERFQ78GAX_6TUimB_PmBXkcVJZ9i+HXbK=N0dmQ@mail.gmail.com>
Date:   Tue, 18 May 2021 14:58:32 +0200
From:   Robert Foss <robert.foss@...aro.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Yu Kuai <yukuai3@...wei.com>, 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 Tue, 18 May 2021 at 09:42, Johan Hovold <johan@...nel.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@...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");

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@...aro.org>