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Subject: Re: [PATCH v1 1/1] PCI/ERR: Handle fatal error recovery for
 non-hotplug capable devices
To:     Yicong Yang <yangyicong@hisilicon.com>, bhelgaas@google.com
Cc:     jay.vosburgh@canonical.com, linux-pci@vger.kernel.org,
        linux-kernel@vger.kernel.org, ashok.raj@intel.com
References: <18609.1588812972@famine>
 <f4bbacd3af453285271c8fc733652969e11b84f8.1588821160.git.sathyanarayanan.kuppuswamy@linux.intel.com>
 <dbb211ba-a5f1-0e4f-64c9-6eb28cd1fb7f@hisilicon.com>
 <2569c75c-41a6-d0f3-ee34-0d288c4e0b61@linux.intel.com>
 <8dd2233c-a636-59fa-4c6e-5da08556d09e@hisilicon.com>
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>
Message-ID: <d59e5312-9f0b-f6b2-042a-363022989b8f@linux.intel.com>
Date:   Thu, 21 May 2020 12:31:33 -0700
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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) {
>>>
>> .
>>
>