Re: [PATCH] [v2] PCI: tegra194: Fix runtime PM imbalance on error

Re: [PATCH] [v2] PCI: tegra194: Fix runtime PM imbalance on error

[Bjorn Helgaas]

[+cc Rafael, linux-pm]

On Thu, May 21, 2020 at 11:13:49AM +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 didn't realize there were so many drivers with the exact same issue.
Can we just squash these all into a single patch so we can see them
all together?

Hmm.  There are over 1300 callers of pm_runtime_get_sync(), and it
looks like many of them have similar issues, i.e., they have a pattern
like this

  ret = pm_runtime_get_sync(dev);
  if (ret < 0)
    return;

  pm_runtime_put(dev);

where there is not a pm_runtime_put() to match every
pm_runtime_get_sync().  Random sample:

  nds32_pmu_reserve_hardware
  sata_rcar_probe
  exynos_trng_probe
  ks_sa_rng_probe
  omap_aes_probe
  sun8i_ss_probe
  omap_aes_probe
  zynq_gpio_probe
  amdgpu_hwmon_show_power_avg
  mtk_crtc_ddp_hw_init
  ...

Surely I'm missing something and these aren't all broken, right?

Maybe we could put together a coccinelle script to scan the tree for
this issue?

> Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
> ---
>  drivers/pci/controller/dwc/pcie-tegra194.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> index ae30a2fd3716..2c0d2ce16b47 100644
> --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> @@ -1623,7 +1623,7 @@ static int tegra_pcie_config_rp(struct tegra_pcie_dw *pcie)
>  	ret = pinctrl_pm_select_default_state(dev);
>  	if (ret < 0) {
>  		dev_err(dev, "Failed to configure sideband pins: %d\n", ret);
> -		goto fail_pinctrl;
> +		goto fail_pm_get_sync;
>  	}
>  
>  	tegra_pcie_init_controller(pcie);
> @@ -1650,9 +1650,8 @@ static int tegra_pcie_config_rp(struct tegra_pcie_dw *pcie)
>  
>  fail_host_init:
>  	tegra_pcie_deinit_controller(pcie);
> -fail_pinctrl:
> -	pm_runtime_put_sync(dev);
>  fail_pm_get_sync:
> +	pm_runtime_put_sync(dev);
>  	pm_runtime_disable(dev);
>  	return ret;
>  }
> -- 
> 2.17.1
> 

Re: [PATCH] [v2] PCI: tegra194: Fix runtime PM imbalance on error

[Rafael J. Wysocki]

On Thu, May 21, 2020 at 5:16 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> [+cc Rafael, linux-pm]
>
> On Thu, May 21, 2020 at 11:13:49AM +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 didn't realize there were so many drivers with the exact same issue.
> Can we just squash these all into a single patch so we can see them
> all together?
>
> Hmm.  There are over 1300 callers of pm_runtime_get_sync(), and it
> looks like many of them have similar issues, i.e., they have a pattern
> like this
>
>   ret = pm_runtime_get_sync(dev);
>   if (ret < 0)
>     return;
>
>   pm_runtime_put(dev);
>
> where there is not a pm_runtime_put() to match every
> pm_runtime_get_sync().  Random sample:
>
>   nds32_pmu_reserve_hardware
>   sata_rcar_probe
>   exynos_trng_probe
>   ks_sa_rng_probe
>   omap_aes_probe
>   sun8i_ss_probe
>   omap_aes_probe
>   zynq_gpio_probe
>   amdgpu_hwmon_show_power_avg
>   mtk_crtc_ddp_hw_init
>   ...
>
> Surely I'm missing something and these aren't all broken, right?

If they do what you've said, they are all broken I'm afraid.

They should all be doing something like

    ret = pm_runtime_get_sync(dev);
    if (ret < 0)
        goto out;

    ...

out:
    pm_runtime_put(dev);

> Maybe we could put together a coccinelle script to scan the tree for
> this issue?
>
> > Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
> > ---
> >  drivers/pci/controller/dwc/pcie-tegra194.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> > index ae30a2fd3716..2c0d2ce16b47 100644
> > --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> > +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> > @@ -1623,7 +1623,7 @@ static int tegra_pcie_config_rp(struct tegra_pcie_dw *pcie)
> >       ret = pinctrl_pm_select_default_state(dev);
> >       if (ret < 0) {
> >               dev_err(dev, "Failed to configure sideband pins: %d\n", ret);
> > -             goto fail_pinctrl;
> > +             goto fail_pm_get_sync;
> >       }
> >
> >       tegra_pcie_init_controller(pcie);
> > @@ -1650,9 +1650,8 @@ static int tegra_pcie_config_rp(struct tegra_pcie_dw *pcie)
> >
> >  fail_host_init:
> >       tegra_pcie_deinit_controller(pcie);
> > -fail_pinctrl:
> > -     pm_runtime_put_sync(dev);
> >  fail_pm_get_sync:
> > +     pm_runtime_put_sync(dev);

Why not pm_runtime_put()?

> >       pm_runtime_disable(dev);
> >       return ret;
> >  }
> > --
> > 2.17.1
> >

Re: Re: [PATCH] [v2] PCI: tegra194: Fix runtime PM imbalance on error

[dinghao.liu]

> On Thu, May 21, 2020 at 5:16 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
> >
> > [+cc Rafael, linux-pm]
> >
> > On Thu, May 21, 2020 at 11:13:49AM +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 didn't realize there were so many drivers with the exact same issue.
> > Can we just squash these all into a single patch so we can see them
> > all together?
> >
> > Hmm.  There are over 1300 callers of pm_runtime_get_sync(), and it
> > looks like many of them have similar issues, i.e., they have a pattern
> > like this
> >
> >   ret = pm_runtime_get_sync(dev);
> >   if (ret < 0)
> >     return;
> >
> >   pm_runtime_put(dev);
> >
> > where there is not a pm_runtime_put() to match every
> > pm_runtime_get_sync().  Random sample:
> >
> >   nds32_pmu_reserve_hardware
> >   sata_rcar_probe
> >   exynos_trng_probe
> >   ks_sa_rng_probe
> >   omap_aes_probe
> >   sun8i_ss_probe
> >   omap_aes_probe
> >   zynq_gpio_probe
> >   amdgpu_hwmon_show_power_avg
> >   mtk_crtc_ddp_hw_init
> >   ...
> >
> > Surely I'm missing something and these aren't all broken, right?
> 
> If they do what you've said, they are all broken I'm afraid.
> 
> They should all be doing something like
> 
>     ret = pm_runtime_get_sync(dev);
>     if (ret < 0)
>         goto out;
> 
>     ...
> 
> out:
>     pm_runtime_put(dev);
> 
> > Maybe we could put together a coccinelle script to scan the tree for
> > this issue?
> >
> > > Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
> > > ---
> > >  drivers/pci/controller/dwc/pcie-tegra194.c | 5 ++---
> > >  1 file changed, 2 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> > > index ae30a2fd3716..2c0d2ce16b47 100644
> > > --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> > > +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> > > @@ -1623,7 +1623,7 @@ static int tegra_pcie_config_rp(struct tegra_pcie_dw *pcie)
> > >       ret = pinctrl_pm_select_default_state(dev);
> > >       if (ret < 0) {
> > >               dev_err(dev, "Failed to configure sideband pins: %d\n", ret);
> > > -             goto fail_pinctrl;
> > > +             goto fail_pm_get_sync;
> > >       }
> > >
> > >       tegra_pcie_init_controller(pcie);
> > > @@ -1650,9 +1650,8 @@ static int tegra_pcie_config_rp(struct tegra_pcie_dw *pcie)
> > >
> > >  fail_host_init:
> > >       tegra_pcie_deinit_controller(pcie);
> > > -fail_pinctrl:
> > > -     pm_runtime_put_sync(dev);
> > >  fail_pm_get_sync:
> > > +     pm_runtime_put_sync(dev);
> 
> Why not pm_runtime_put()?\x10

Good question. For functions with PM decrement API somewhere, I 
will adopt it. If this API is not suitable here, please tell me.

> 
> > >       pm_runtime_disable(dev);
> > >       return ret;
> > >  }
> > > --
> > > 2.17.1
> > >

Re: Re: [PATCH] [v2] PCI: tegra194: Fix runtime PM imbalance on error

[dinghao.liu]

Hi Bjorn,

In fact, most usage of pm_runtime_get_sync() is correct. I made 
a static analysis tool to check this imbalance in kernel and 
found about 80 bugs in dirvers. Some of my patches have been 
accepted and I'm trying to patch the rest as soon as possible.

Regards,
Dinghao 

> [+cc Rafael, linux-pm]
> 
> On Thu, May 21, 2020 at 11:13:49AM +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 didn't realize there were so many drivers with the exact same issue.
> Can we just squash these all into a single patch so we can see them
> all together?
> 
> Hmm.  There are over 1300 callers of pm_runtime_get_sync(), and it
> looks like many of them have similar issues, i.e., they have a pattern
> like this
> 
>   ret = pm_runtime_get_sync(dev);
>   if (ret < 0)
>     return;
> 
>   pm_runtime_put(dev);
> 
> where there is not a pm_runtime_put() to match every
> pm_runtime_get_sync().  Random sample:
> 
>   nds32_pmu_reserve_hardware
>   sata_rcar_probe
>   exynos_trng_probe
>   ks_sa_rng_probe
>   omap_aes_probe
>   sun8i_ss_probe
>   omap_aes_probe
>   zynq_gpio_probe
>   amdgpu_hwmon_show_power_avg
>   mtk_crtc_ddp_hw_init
>   ...
> 
> Surely I'm missing something and these aren't all broken, right?
> 
> Maybe we could put together a coccinelle script to scan the tree for
> this issue?
> 
> > Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
> > ---
> >  drivers/pci/controller/dwc/pcie-tegra194.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> > index ae30a2fd3716..2c0d2ce16b47 100644
> > --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> > +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> > @@ -1623,7 +1623,7 @@ static int tegra_pcie_config_rp(struct tegra_pcie_dw *pcie)
> >  	ret = pinctrl_pm_select_default_state(dev);
> >  	if (ret < 0) {
> >  		dev_err(dev, "Failed to configure sideband pins: %d\n", ret);
> > -		goto fail_pinctrl;
> > +		goto fail_pm_get_sync;
> >  	}
> >  
> >  	tegra_pcie_init_controller(pcie);
> > @@ -1650,9 +1650,8 @@ static int tegra_pcie_config_rp(struct tegra_pcie_dw *pcie)
> >  
> >  fail_host_init:
> >  	tegra_pcie_deinit_controller(pcie);
> > -fail_pinctrl:
> > -	pm_runtime_put_sync(dev);
> >  fail_pm_get_sync:
> > +	pm_runtime_put_sync(dev);
> >  	pm_runtime_disable(dev);
> >  	return ret;
> >  }
> > -- 
> > 2.17.1
> >