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

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Date:   Fri, 22 May 2020 12:36:51 +0800 (GMT+08:00)
From:   dinghao.liu@....edu.cn
To:     "Bjorn Helgaas" <helgaas@...nel.org>
Cc:     kjlu@....edu, "Lorenzo Pieralisi" <lorenzo.pieralisi@....com>,
        "Rob Herring" <robh@...nel.org>,
        "Bjorn Helgaas" <bhelgaas@...gle.com>,
        "Thierry Reding" <thierry.reding@...il.com>,
        "Jonathan Hunter" <jonathanh@...dia.com>,
        "Vidya Sagar" <vidyas@...dia.com>,
        "Andrew Murray" <amurray@...goodpenguin.co.uk>,
        linux-pci@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org
Subject: Re: Re: [PATCH] [v2] PCI: tegra194: Fix runtime PM imbalance on
 error

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@....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
> >