linux-kernel - Re: [PATCH] media: vsp1: Fix runtime PM imbalance in vsp1

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Message-ID: <20200608015753.GK22208@pendragon.ideasonboard.com>
Date:   Mon, 8 Jun 2020 04:57:53 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Dinghao Liu <dinghao.liu@....edu.cn>
Cc:     kjlu@....edu,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: vsp1: Fix runtime PM imbalance in vsp1_probe

On Mon, Jun 08, 2020 at 04:54:57AM +0300, Laurent Pinchart wrote:
> Hi Dinghao,
> 
> Thank you for the patch.
> 
> On Sat, May 23, 2020 at 07:54:26PM +0800, Dinghao Liu wrote:
> > pm_runtime_get_sync() increments the runtime PM usage counter even
> > when it returns an error code. Thus a pairing decrement is needed on
> > the error handling path to keep the counter balanced.
> 
> I wonder how many bugs we have today, and how many bugs will keep
> appearing in the future, due to this historical design mistake :-( 
> 
> > Signed-off-by: Dinghao Liu <dinghao.liu@....edu.cn>
> > ---
> >  drivers/media/platform/vsp1/vsp1_drv.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/media/platform/vsp1/vsp1_drv.c b/drivers/media/platform/vsp1/vsp1_drv.c
> > index c650e45bb0ad..017a54f2fdd8 100644
> > --- a/drivers/media/platform/vsp1/vsp1_drv.c
> > +++ b/drivers/media/platform/vsp1/vsp1_drv.c
> > @@ -846,8 +846,10 @@ static int vsp1_probe(struct platform_device *pdev)
> >  	pm_runtime_enable(&pdev->dev);
> >  
> >  	ret = pm_runtime_get_sync(&pdev->dev);
> > -	if (ret < 0)
> > +	if (ret < 0) {
> > +		pm_runtime_put_sync(&pdev->dev);
> >  		goto done;
> > +	}
> 
> This change looks good to me, but we also need a similar change in the
> vsp1_device_get() function if I'm not mistaken. Could you combine both
> in the same patch ?

And actually, after fixing vsp1_device_get(), we should replace the
pm_runtime_get_sync() call here with vsp1_device_get(), and the
pm_runtime_put_sync() below with vsp1_device_put(), so there would be no
need to call pm_runtime_put_sync() manually in the error path here.

> >  
> >  	vsp1->version = vsp1_read(vsp1, VI6_IP_VERSION);
> >  	pm_runtime_put_sync(&pdev->dev);

-- 
Regards,

Laurent Pinchart