[PATCH] media: vsp1: Fix runtime PM imbalance in vsp1_probe

[PATCH] media: vsp1: Fix runtime PM imbalance in vsp1_probe

[Dinghao Liu]

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.

Signed-off-by: Dinghao Liu <dinghao.liu@zju.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;
+	}
 
 	vsp1->version = vsp1_read(vsp1, VI6_IP_VERSION);
 	pm_runtime_put_sync(&pdev->dev);
-- 
2.17.1

Re: [PATCH] media: vsp1: Fix runtime PM imbalance in vsp1_probe

[Laurent Pinchart]

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@zju.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 ?

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

-- 
Regards,

Laurent Pinchart

Re: [PATCH] media: vsp1: Fix runtime PM imbalance in vsp1_probe

[Laurent Pinchart]

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@zju.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

Re: Re: [PATCH] media: vsp1: Fix runtime PM imbalance in vsp1_probe

[dinghao.liu]

Hi Laurent,

> > 
> > I wonder how many bugs we have today, and how many bugs will keep
> > appearing in the future, due to this historical design mistake :-( 
> > 

Good question. It's hard to say if this is a design mistake (some use
of this API does not check its return value and expects it always to
increment the usage counter). But it does make developers misuse it easier.

> > 
> > 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 ?
> 

Thank you for your advice! I think you are right and I will fix this in the
next version of 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.
> 

The parameter type of vsp1_device_get() and vsp1_device_put() is "struct 
vsp1_device". If we want to use these two wrappers, we need to adjust their 
parameter type to "struct platform_device" or "struct device", which may 
lead to errors in other callers. Maybe we should leave it as it is.

Regards,
Dinghao

Re: Re: [PATCH] media: vsp1: Fix runtime PM imbalance in vsp1_probe

[Laurent Pinchart]

Hi Dianghao,

On Mon, Jun 08, 2020 at 11:03:26AM +0800, dinghao.liu@zju.edu.cn wrote:
> Hi Laurent,
> 
> > > I wonder how many bugs we have today, and how many bugs will keep
> > > appearing in the future, due to this historical design mistake :-( 
> 
> Good question. It's hard to say if this is a design mistake (some use
> of this API does not check its return value and expects it always to
> increment the usage counter). But it does make developers misuse it easier.
> 
> > > 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 ?
> 
> Thank you for your advice! I think you are right and I will fix this in the
> next version of 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.
> 
> The parameter type of vsp1_device_get() and vsp1_device_put() is "struct 
> vsp1_device". If we want to use these two wrappers, we need to adjust their 
> parameter type to "struct platform_device" or "struct device", which may 
> lead to errors in other callers. Maybe we should leave it as it is.

The vsp1_probe() function has a struct vsp1_device whose dev field is
populated by the time it needs to call pm_runtime_get_sync() and
pm_runtime_get_put(), so I think you can use vsp1_device_get() and
vsp1_device_put() as drop-in replacements without changing the
parameters to these two functions.

-- 
Regards,

Laurent Pinchart

Re: Re: Re: [PATCH] media: vsp1: Fix runtime PM imbalance in vsp1_probe

[dinghao.liu]

> 
> The vsp1_probe() function has a struct vsp1_device whose dev field is
> populated by the time it needs to call pm_runtime_get_sync() and
> pm_runtime_get_put(), so I think you can use vsp1_device_get() and
> vsp1_device_put() as drop-in replacements without changing the
> parameters to these two functions.
> 

It's clear to me, thanks!

Regards,
Dinghao

Re: Re: [PATCH] media: vsp1: Fix runtime PM imbalance in vsp1_probe

[Geert Uytterhoeven]

Hi Dinghao,

On Mon, Jun 8, 2020 at 5:03 AM <dinghao.liu@zju.edu.cn> wrote:
> > > I wonder how many bugs we have today, and how many bugs will keep
> > > appearing in the future, due to this historical design mistake :-(
>
> Good question. It's hard to say if this is a design mistake (some use
> of this API does not check its return value and expects it always to
> increment the usage counter). But it does make developers misuse it easier.

On Renesas SoCs, I believe these can only fail if there's something
seriously wrong, which means the system could never have gotten this far
in the boot sequence anyway.  That's why I tend not to check the result
of pm_runtime_get_sync() at all (on drivers for Renesas SoCs).

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: Re: [PATCH] media: vsp1: Fix runtime PM imbalance in vsp1_probe

[Laurent Pinchart]

Hi Geert,

On Mon, Jun 08, 2020 at 09:39:51AM +0200, Geert Uytterhoeven wrote:
> Hi Dinghao,
> 
> On Mon, Jun 8, 2020 at 5:03 AM <dinghao.liu@zju.edu.cn> wrote:
> > > > I wonder how many bugs we have today, and how many bugs will keep
> > > > appearing in the future, due to this historical design mistake :-(
> >
> > Good question. It's hard to say if this is a design mistake (some use
> > of this API does not check its return value and expects it always to
> > increment the usage counter). But it does make developers misuse it easier.
> 
> On Renesas SoCs, I believe these can only fail if there's something
> seriously wrong, which means the system could never have gotten this far
> in the boot sequence anyway.  That's why I tend not to check the result
> of pm_runtime_get_sync() at all (on drivers for Renesas SoCs).

There are lots of return paths from rpm_resume() that return an error,
more than just rpm_callback(). Do you consider that none of them are
valid errors that drivers need to handle ?

-- 
Regards,

Laurent Pinchart