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Date:   Thu, 21 May 2020 17:25:14 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Dinghao Liu <dinghao.liu@....edu.cn>
Cc:     Kangjie Lu <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 <linux-pci@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] [v2] PCI: tegra194: Fix runtime PM imbalance on error

On Thu, May 21, 2020 at 5:16 PM Bjorn Helgaas <helgaas@...nel.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@....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
> >

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