linux-kernel - Re: [PATCH v12 07/15] PCI/ERR: Use "bridge" for clarity in pcie_do

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Message-ID: <20201202231859.GA1484005@bjorn-Precision-5520>
Date:   Wed, 2 Dec 2020 17:18:59 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sean V Kelley <sean.v.kelley@...el.com>
Cc:     bhelgaas@...gle.com, Jonathan.Cameron@...wei.com,
        xerces.zhao@...il.com, rafael.j.wysocki@...el.com,
        ashok.raj@...el.com, tony.luck@...el.com,
        sathyanarayanan.kuppuswamy@...el.com, qiuxu.zhuo@...el.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH v12 07/15] PCI/ERR: Use "bridge" for clarity in
 pcie_do_recovery()

On Fri, Nov 20, 2020 at 04:10:28PM -0800, Sean V Kelley wrote:
> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> index 7a5af873d8bc..46a5b84f8842 100644
> --- a/drivers/pci/pcie/err.c
> +++ b/drivers/pci/pcie/err.c
> @@ -151,24 +151,27 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>  		pci_ers_result_t (*reset_subordinates)(struct pci_dev *pdev))
>  {
>  	int type = pci_pcie_type(dev);
> -	pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
> +	struct pci_dev *bridge;
>  	struct pci_bus *bus;
> +	pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
>  
>  	/*
> -	 * Error recovery runs on all subordinates of the first downstream port.
> -	 * If the downstream port detected the error, it is cleared at the end.
> +	 * Error recovery runs on all subordinates of the bridge.  If the
> +	 * bridge detected the error, it is cleared at the end.
>  	 */
>  	if (!(type == PCI_EXP_TYPE_ROOT_PORT ||
>  	      type == PCI_EXP_TYPE_DOWNSTREAM))
> -		dev = pci_upstream_bridge(dev);
> -	bus = dev->subordinate;
> +		bridge = pci_upstream_bridge(dev);
> +	else
> +		bridge = dev;

I think there's a bug here even before your series.  We started with:

  pcie_do_recovery(struct pci_dev *dev, ..., pci_ers_result_t (*reset_link)())
  {
    if (!(pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
	  pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM))
      dev = dev->bus->self;
    ...
    reset_link(dev);

so if we called pcie_do_recovery() with an Endpoint, we set "dev" to
the upstream bridge, either a Root Port or a Switch Downstream Port,
which we then pass on to reset_link().  For native AER and APEI,
that's aer_root_reset(), which assumes it gets a Root Port.

If we pass a Switch Downstream Port, aer_root_reset() writes to the
*switch port's* PCI_ERR_ROOT_COMMAND and PCI_ERR_ROOT_STATUS, which
are reserved since it's not a Root Port or an RCEC.

The writes probably don't *break* anything since those registers are
reserved, but they also don't disable the interrupt or clear the Root
Error Status.

Bjorn