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

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Message-ID: <2a46539d.b977f.1723553aa81.Coremail.dinghao.liu@zju.edu.cn>
Date:   Thu, 21 May 2020 11:42:55 +0800 (GMT+08:00)
From:   dinghao.liu@....edu.cn
To:     "Dan Carpenter" <dan.carpenter@...cle.com>
Cc:     "Dmitry Osipenko" <digetx@...il.com>, kjlu@....edu,
        devel@...verdev.osuosl.org,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        "Jonathan Hunter" <jonathanh@...dia.com>,
        "Thierry Reding" <thierry.reding@...il.com>,
        linux-tegra@...r.kernel.org,
        "Mauro Carvalho Chehab" <mchehab@...nel.org>,
        linux-media@...r.kernel.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Pavel Machek" <pavel@....cz>, "Len Brown" <len.brown@...el.com>,
        linux-pm@...r.kernel.org
Subject: Re: Re: [PATCH] media: staging: tegra-vde: fix runtime pm imbalance
 on error

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

&quot;Dan Carpenter&quot; &lt;dan.carpenter@...cle.com&gt;写道：
> On Wed, May 20, 2020 at 01:15:44PM +0300, Dmitry Osipenko wrote:
> > 20.05.2020 12:51, Dinghao Liu пишет:
> > > 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@....edu.cn>
> > > ---
> > >  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@gmail.com/
> > 
> > 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);