Re: [PATCH 2/4] PCI: Fix runtime PM usage count underflow

[Lukas Wunner <lukas@wunner.de>]

[cc += Rafael, Mika]

On Sun, Jun 08, 2025 at 08:58:02PM -0500, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@amd.com>
> 
> When a USB4 dock is unplugged the PCIe bridge it's connected to will
> remove issue a "Link Down" and "Card not detected event". The PCI core

Nit: s/remove//

> will treat this as a surprise hotplug event and unconfigure all downstream
> devices. This involves setting the device error state to
> `pci_channel_io_perm_failure`.
> 
> When PCI core gets to the point that the device is removed using
> pci_device_remove() the runtime count has already been decremented and
> so calling pm_runtime_put_sync() will cause an underflow.

Where has it been decremented?  I think this needs to be identified
and a Fixes tag added.

> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -479,7 +479,8 @@ static void pci_device_remove(struct device *dev)
>  	pci_iov_remove(pci_dev);
>  
>  	/* Undo the runtime PM settings in local_pci_probe() */
> -	pm_runtime_put_sync(dev);
> +	if (pci_dev->error_state != pci_channel_io_perm_failure)
> +		pm_runtime_put_sync(dev);

Usually pci_dev_is_disconnected() is used in lieu of checking for
the error_state directly.

Thanks,

Lukas