Re: Re: [PATCH] media: staging: tegra-vde: fix runtime pm imbalance on error

From: dinghao . liu
Date: Wed May 20 2020 - 23:43:35 EST


Hi, Dan,

I agree the best solution is to fix __pm_runtime_resume(). But there are also
many cases that assume pm_runtime_get_sync() will change PM usage
counter on error. According to my static analysis results, the number of these
"right" cases are larger. Adjusting __pm_runtime_resume() directly will introduce
more new bugs. Therefore I think we should resolve the "bug" cases individually.

I think that Dmitry's patch is more reasonable than mine.

Dinghao

"Dan Carpenter" <dan.carpenter@xxxxxxxxxx>åéï
> On Wed, May 20, 2020 at 01:15:44PM +0300, Dmitry Osipenko wrote:
> > 20.05.2020 12:51, Dinghao Liu ÐÐÑÐÑ:
> > > pm_runtime_get_sync() increments the runtime PM usage counter even
> > > 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@xxxxxxxxxx>
> > > ---
> > > drivers/staging/media/tegra-vde/vde.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/staging/media/tegra-vde/vde.c b/drivers/staging/media/tegra-vde/vde.c
> > > index d3e63512a765..dd134a3a15c7 100644
> > > --- a/drivers/staging/media/tegra-vde/vde.c
> > > +++ b/drivers/staging/media/tegra-vde/vde.c
> > > @@ -777,7 +777,7 @@ static int tegra_vde_ioctl_decode_h264(struct tegra_vde *vde,
> > >
> > > ret = pm_runtime_get_sync(dev);
> > > if (ret < 0)
> > > - goto unlock;
> > > + goto put_runtime_pm;
> > >
> > > /*
> > > * We rely on the VDE registers reset value, otherwise VDE
> > >
> >
> > Hello Dinghao,
> >
> > Thank you for the patch. I sent out a similar patch a week ago [1].
> >
> > [1]
> > https://patchwork.ozlabs.org/project/linux-tegra/patch/20200514210847.9269-2-digetx@xxxxxxxxx/
> >
> > The pm_runtime_put_noidle() should have the same effect as yours
> > variant, although my variant won't change the last_busy RPM time, which
> > I think is a bit more appropriate behavior.
>
> I don't think either patch is correct. The right thing to do is to fix
> __pm_runtime_resume() so it doesn't leak a reference count on error.
>
> The problem is that a lot of functions don't check the return so
> possibly we are relying on that behavior. We may need to introduce a
> new function which cleans up properly instead of leaking reference
> counts?
>
> Also it's not documented that pm_runtime_get_sync() returns 1 sometimes
> on success so it leads to a few bugs.
>
> drivers/gpu/drm/stm/ltdc.c: ret = pm_runtime_get_sync(ddev->dev);
> drivers/gpu/drm/stm/ltdc.c- if (ret) {
> --
> drivers/gpu/drm/stm/ltdc.c: ret = pm_runtime_get_sync(ddev->dev);
> drivers/gpu/drm/stm/ltdc.c- if (ret) {
>
> drivers/media/platform/mtk-vcodec/mtk_vcodec_dec_pm.c: ret = pm_runtime_get_sync(pm->dev);
> drivers/media/platform/mtk-vcodec/mtk_vcodec_dec_pm.c- if (ret)
>
> drivers/media/platform/ti-vpe/cal.c: ret = pm_runtime_get_sync(&pdev->dev);
> drivers/media/platform/ti-vpe/cal.c- if (ret)
>
> drivers/mfd/arizona-core.c: ret = pm_runtime_get_sync(arizona->dev);
> drivers/mfd/arizona-core.c- if (ret != 0)
>
> drivers/remoteproc/qcom_q6v5_adsp.c: ret = pm_runtime_get_sync(adsp->dev);
> drivers/remoteproc/qcom_q6v5_adsp.c- if (ret)
>
> drivers/spi/spi-img-spfi.c: ret = pm_runtime_get_sync(dev);
> drivers/spi/spi-img-spfi.c- if (ret)
>
> drivers/usb/dwc3/dwc3-pci.c: ret = pm_runtime_get_sync(&dwc3->dev);
> drivers/usb/dwc3/dwc3-pci.c- if (ret)
>
> drivers/watchdog/rti_wdt.c: ret = pm_runtime_get_sync(dev);
> drivers/watchdog/rti_wdt.c- if (ret) {
>
> regards,
> dan carpenter
>
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 99c7da112c95..e280991a977d 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -1082,6 +1082,9 @@ int __pm_runtime_resume(struct device *dev, int rpmflags)
> retval = rpm_resume(dev, rpmflags);
> spin_unlock_irqrestore(&dev->power.lock, flags);
>
> + if (retval < 0 && rpmflags & RPM_GET_PUT)
> + atomic_dec(&dev->power.usage_count);
> +
> return retval;
> }
> EXPORT_SYMBOL_GPL(__pm_runtime_resume);