linux-kernel - Re: [PATCH v1 1/1] PCI/ERR: Handle fatal error recovery for non-hotplug capable devices

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Date:   Wed, 20 May 2020 16:28:18 +0800
From:   Yicong Yang <yangyicong@...ilicon.com>
To:     <sathyanarayanan.kuppuswamy@...ux.intel.com>, <bhelgaas@...gle.com>
CC:     <jay.vosburgh@...onical.com>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <ashok.raj@...el.com>
Subject: Re: [PATCH v1 1/1] PCI/ERR: Handle fatal error recovery for
 non-hotplug capable devices

On 2020/5/7 11:32, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
>
> If there are non-hotplug capable devices connected to a given
> port, then during the fatal error recovery(triggered by DPC or
> AER), after calling reset_link() function, we cannot rely on
> hotplug handler to detach and re-enumerate the device drivers
> in the affected bus. Instead, we will have to let the error
> recovery handler call report_slot_reset() for all devices in
> the bus to notify about the reset operation. Although this is
> only required for non hot-plug capable devices, doing it for
> hotplug capable devices should not affect the functionality.
>
> Along with above issue, this fix also applicable to following
> issue.
>
> Commit 6d2c89441571 ("PCI/ERR: Update error status after
> reset_link()") added support to store status of reset_link()
> call. Although this fixed the error recovery issue observed if
> the initial value of error status is PCI_ERS_RESULT_DISCONNECT
> or PCI_ERS_RESULT_NO_AER_DRIVER, it also discarded the status
> result from report_frozen_detected. This can cause a failure to
> recover if _NEED_RESET is returned by report_frozen_detected and
> report_slot_reset is not invoked.
>
> Such an event can be induced for testing purposes by reducing the
> Max_Payload_Size of a PCIe bridge to less than that of a device
> downstream from the bridge, and then initiating I/O through the
> device, resulting in oversize transactions.  In the presence of DPC,
> this results in a containment event and attempted reset and recovery
> via pcie_do_recovery.  After 6d2c89441571 report_slot_reset is not
> invoked, and the device does not recover.
>
> [original patch is from jay.vosburgh@...onical.com]
> [original patch link https://lore.kernel.org/linux-pci/18609.1588812972@famine/]
> Fixes: 6d2c89441571 ("PCI/ERR: Update error status after reset_link()")
> Signed-off-by: Jay Vosburgh <jay.vosburgh@...onical.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> ---
>  drivers/pci/pcie/err.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> index 14bb8f54723e..db80e1ecb2dc 100644
> --- a/drivers/pci/pcie/err.c
> +++ b/drivers/pci/pcie/err.c
> @@ -165,13 +165,24 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>  	pci_dbg(dev, "broadcast error_detected message\n");
>  	if (state == pci_channel_io_frozen) {
>  		pci_walk_bus(bus, report_frozen_detected, &status);
> -		status = reset_link(dev);
> -		if (status != PCI_ERS_RESULT_RECOVERED) {
> +		status = PCI_ERS_RESULT_NEED_RESET;
> +	} else {
> +		pci_walk_bus(bus, report_normal_detected, &status);
> +	}
> +
> +	if (status == PCI_ERS_RESULT_NEED_RESET) {
> +		if (reset_link) {
> +			if (reset_link(dev) != PCI_ERS_RESULT_RECOVERED)

we'll call reset_link() only if link is frozen. so it may have problem here.

Thanks,
Yicong


> +				status = PCI_ERS_RESULT_DISCONNECT;
> +		} else {
> +			if (pci_bus_error_reset(dev))
> +				status = PCI_ERS_RESULT_DISCONNECT;
> +		}
> +
> +		if (status == PCI_ERS_RESULT_DISCONNECT) {
>  			pci_warn(dev, "link reset failed\n");
>  			goto failed;
>  		}
> -	} else {
> -		pci_walk_bus(bus, report_normal_detected, &status);
>  	}
>  
>  	if (status == PCI_ERS_RESULT_CAN_RECOVER) {