linux-kernel - Re: [PATCH v2] PCI/PM: Avoid suspending the device with errors

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Message-ID: <20250422194537.GA380850@bhelgaas>
Date: Tue, 22 Apr 2025 14:45:37 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Raag Jadav <raag.jadav@...el.com>
Cc: rafael@...nel.org, mahesh@...ux.ibm.com, oohall@...il.com,
	bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, ilpo.jarvinen@...ux.intel.com,
	lukas@...ner.de, aravind.iddamsetty@...ux.intel.com
Subject: Re: [PATCH v2] PCI/PM: Avoid suspending the device with errors

On Tue, Apr 22, 2025 at 07:23:41PM +0530, Raag Jadav wrote:
> If an error is triggered before or during system suspend, any bus level
> power state transition will result in unpredictable behaviour by the
> device with failed recovery. Avoid suspending such a device and leave
> it in its existing power state.
> 
> This only covers the devices that rely on PCI core PM for their power
> state transition.
> 
> Signed-off-by: Raag Jadav <raag.jadav@...el.com>
> ---
> 
> v2: Synchronize AER handling with PCI PM (Rafael)
> 
> More discussion on [1].
> [1] https://lore.kernel.org/all/CAJZ5v0g-aJXfVH+Uc=9eRPuW08t-6PwzdyMXsC6FZRKYJtY03Q@mail.gmail.com/

Thanks for the pointer, but the commit log for this patch needs to be
complete in itself.  "Unpredictable behavior" is kind of hand-wavy and
doesn't really help understand the problem.

>  drivers/pci/pci-driver.c |  3 ++-
>  drivers/pci/pcie/aer.c   | 11 +++++++++++
>  include/linux/aer.h      |  2 ++
>  3 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index f57ea36d125d..289a1fa7cb2d 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -884,7 +884,8 @@ static int pci_pm_suspend_noirq(struct device *dev)
>  		}
>  	}
>  
> -	if (!pci_dev->state_saved) {
> +	/* Avoid suspending the device with errors */
> +	if (!pci_aer_in_progress(pci_dev) && !pci_dev->state_saved) {

This looks potentially racy, since hardware can set bits in
PCI_EXP_DEVSTA at any time.

The comment restates the C code, but doesn't say *why*.  The "why" is
important for ongoing maintenance.

>  		pci_save_state(pci_dev);
>  
>  		/*
> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
> index 508474e17183..b70f5011d4f5 100644
> --- a/drivers/pci/pcie/aer.c
> +++ b/drivers/pci/pcie/aer.c
> @@ -233,6 +233,17 @@ int pcie_aer_is_native(struct pci_dev *dev)
>  }
>  EXPORT_SYMBOL_NS_GPL(pcie_aer_is_native, "CXL");
>  
> +bool pci_aer_in_progress(struct pci_dev *dev)
> +{
> +	u16 reg16;
> +
> +	if (!pcie_aer_is_native(dev))
> +		return false;
> +
> +	pcie_capability_read_word(dev, PCI_EXP_DEVSTA, &reg16);
> +	return !!(reg16 & PCI_EXP_AER_FLAGS);
> +}
> +
>  static int pci_enable_pcie_error_reporting(struct pci_dev *dev)
>  {
>  	int rc;
> diff --git a/include/linux/aer.h b/include/linux/aer.h
> index 947b63091902..68ae5378256e 100644
> --- a/include/linux/aer.h
> +++ b/include/linux/aer.h
> @@ -48,12 +48,14 @@ struct aer_capability_regs {
>  #if defined(CONFIG_PCIEAER)
>  int pci_aer_clear_nonfatal_status(struct pci_dev *dev);
>  int pcie_aer_is_native(struct pci_dev *dev);
> +bool pci_aer_in_progress(struct pci_dev *dev);
>  #else
>  static inline int pci_aer_clear_nonfatal_status(struct pci_dev *dev)
>  {
>  	return -EINVAL;
>  }
>  static inline int pcie_aer_is_native(struct pci_dev *dev) { return 0; }
> +static inline bool pci_aer_in_progress(struct pci_dev *dev) { return false; }
>  #endif
>  
>  void pci_print_aer(struct pci_dev *dev, int aer_severity,
> -- 
> 2.34.1
>