linux-kernel - Re: [PATCH] PCI/sysfs: Ensure devices are powered for config reads

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Message-ID: <CAPAsAGx6C4PdODuTVxc2un=wpDC1azcO5GUa5cH7KwC=bHF-7w@mail.gmail.com>
Date: Tue, 23 Sep 2025 19:56:12 +0200
From: Andrey Ryabinin <ryabinin.a.a@...il.com>
To: Brian Norris <briannorris@...omium.org>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, linux-kernel@...r.kernel.org, 
	linux-pci@...r.kernel.org, Brian Norris <briannorris@...gle.com>, stable@...r.kernel.org
Subject: Re: [PATCH] PCI/sysfs: Ensure devices are powered for config reads

On Fri, Aug 22, 2025 at 10:10 PM Brian Norris <briannorris@...omium.org> wrote:
>
> From: Brian Norris <briannorris@...gle.com>
>
> max_link_speed, max_link_width, current_link_speed, current_link_width,
> secondary_bus_number, and subordinate_bus_number all access config
> registers, but they don't check the runtime PM state. If the device is
> in D3cold, we may see -EINVAL or even bogus values.

I've hit this bug as well, except in my case the device was behind a
suspended PCI
bridge, which seems to block config space accesses.

>
> Wrap these access in pci_config_pm_runtime_{get,put}() like most of the
                       accesses

> rest of the similar sysfs attributes.
>
> Fixes: 56c1af4606f0 ("PCI: Add sysfs max_link_speed/width, current_link_speed/width, etc")
> Cc: stable@...r.kernel.org
> Signed-off-by: Brian Norris <briannorris@...gle.com>
> Signed-off-by: Brian Norris <briannorris@...omium.org>
> ---
>
>  drivers/pci/pci-sysfs.c | 32 +++++++++++++++++++++++++++++---
>  1 file changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 5eea14c1f7f5..160df897dc5e 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -191,9 +191,16 @@ static ssize_t max_link_speed_show(struct device *dev,
>                                    struct device_attribute *attr, char *buf)
>  {
>         struct pci_dev *pdev = to_pci_dev(dev);
> +       ssize_t ret;
> +
> +       pci_config_pm_runtime_get(pdev);
>
> -       return sysfs_emit(buf, "%s\n",
> -                         pci_speed_string(pcie_get_speed_cap(pdev)));
> +       ret = sysfs_emit(buf, "%s\n",
> +                        pci_speed_string(pcie_get_speed_cap(pdev)));

pci_speed_string() & pcie_get_speed_cap() don't access config space,
so no need to change this one.

> +
> +       pci_config_pm_runtime_put(pdev);
> +
> +       return ret;