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

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Date:   Fri, 22 May 2020 14:06:51 +0800 (GMT+08:00)
From:   dinghao.liu@....edu.cn
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Bjorn Helgaas" <helgaas@...nel.org>, "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: 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()?.

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
> > >