| Message ID | 20200523115426.19285-1-dinghao.liu@zju.edu.cn (mailing list archive) |
|---|---|
| State | New |
| Delegated to: | Kieran Bingham |
| Headers | show |
| Series | media: vsp1: Fix runtime PM imbalance in vsp1_probe | expand |
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);
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);
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
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.
> > 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
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
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 ?
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);
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(-)