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SubjectRe: [PATCH v1 1/1] PCI/ERR: Handle fatal error recovery for non-hotplug capable devices
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On 5/21/20 3:58 AM, Yicong Yang wrote:
> On 2020/5/21 1:04, Kuppuswamy, Sathyanarayanan wrote:
>>
>>
>> On 5/20/20 1:28 AM, Yicong Yang wrote:
>>> On 2020/5/7 11:32, sathyanarayanan.kuppuswamy@linux.intel.com wrote:
>>>> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.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@canonical.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@canonical.com>
>>>> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.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.
>> you mean before this change right?
>> After this change, reset_link() will be called as long as status is
>> PCI_ERS_RESULT_NEED_RESET.
>
> Yes. I think we should reset the link only if the io is blocked as before. There's
> no reason to reset a normal link.
Currently, only AER and DPC driver uses pcie_do_recovery() call. So the
possible reset_link options are dpc_reset_link() and aer_root_reset().

In dpc_reset_link() case, the link is already disabled and hence we
don't need to do another reset. In case of aer_root_reset() it
uses pci_bus_error_reset() to reset the slot.
>
> Furthermore, PCI_ERS_RESULT_NEED_RESET means device driver requires a slot reset rather
> than a link reset, so it maybe improper to use it to judge whether a link reset is needed.
> We decide whether to do a link reset only by the io state.
>
> Thanks,
> Yicong
>
>
>>>
>>> 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) {
>>>
>> .
>>
>

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