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

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Date:   Thu, 21 May 2020 10:16:20 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Dinghao Liu <dinghao.liu@....edu.cn>
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: [PATCH] [v2] PCI: tegra194: Fix runtime PM imbalance on error

[+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
>