Re: [PATCH v6 2/2] PCI/ERR: Split the fatal and non-fatal error recovery handling

Kuppuswamy, Sathyanarayanan
2020-10-15T20:12:34Z

On 10/15/20 6:55 AM, Ethan Zhao wrote:
> On Wed, Oct 14, 2020 at 5:00 PM Kuppuswamy Sathyanarayanan
> <sathyanarayanan.nkuppuswamy@gmail.com> wrote:
>>
>> Commit bdb5ac85777d ("PCI/ERR: Handle fatal error recovery")
>> merged fatal and non-fatal error recovery paths, and also made
>> recovery code depend on hotplug handler for "remove affected
>> device + rescan" support. But this change also complicated the
>> error recovery path and which in turn led to the following
>> issues.
>>
>> 1. We depend on hotplug handler for removing the affected
>> devices/drivers on DLLSC LINK down event (on DPC event
>> trigger) and DPC handler for handling the error recovery. Since
>> both handlers operate on same set of affected devices, it leads
>> to race condition, which in turn leads to NULL pointer
>> exceptions or error recovery failures.You can find more details
>> about this issue in following link.
>>
>> https://lore.kernel.org/linux-pci/20201007113158.48933-1-haifeng.zhao@intel.com/T/#t
>>
>> 2. For non-hotplug capable devices fatal (DPC) error recovery
>> is currently broken. Current fatal error recovery implementation
>> relies on PCIe hotplug (pciehp) handler for detaching and
>> re-enumerating the affected devices/drivers. So when dealing with
>> non-hotplug capable devices, recovery code does not restore the state
>> of the affected devices correctly. You can find more details about
>> this issue in the following links.
>>
>> https://lore.kernel.org/linux-pci/20200527083130.4137-1-Zhiqiang.Hou@nxp.com/
>> https://lore.kernel.org/linux-pci/12115.1588207324@famine/
>> https://lore.kernel.org/linux-pci/0e6f89cd6b9e4a72293cc90fafe93487d7c2d295.1585000084.git.sathyanarayanan.kuppuswamy@linux.intel.com/
>>
>> In order to fix the above two issues, we should stop relying on hotplug
>> handler for cleaning the affected devices/drivers and let error recovery
>> handler own this functionality. So this patch reverts Commit bdb5ac85777d
>> ("PCI/ERR: Handle fatal error recovery") and re-introduce the "remove
>> affected device + rescan" functionality in fatal error recovery handler.
>>
>> Also holding pci_lock_rescan_remove() will prevent the race between hotplug
>> and DPC handler.
>>
>> Fixes: bdb5ac85777d ("PCI/ERR: Handle fatal error recovery")
>> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
>> Reviewed-by: Sinan Kaya <okaya@kernel.org>
>> ---
>> Changes since v4:
>> * Added new interfaces for error recovery (pcie_do_fatal_recovery()
>> and pcie_do_nonfatal_recovery()).
>>
>> Changes since v5:
>> * Fixed static/non-static declartion issue.
>>
>> Documentation/PCI/pci-error-recovery.rst | 47 ++++++++++------
>> Documentation/PCI/pcieaer-howto.rst | 2 +-
>> drivers/pci/pci.h | 5 +-
>> drivers/pci/pcie/aer.c | 10 ++--
>> drivers/pci/pcie/dpc.c | 2 +-
>> drivers/pci/pcie/edr.c | 2 +-
>> drivers/pci/pcie/err.c | 70 ++++++++++++++++++------
>> 7 files changed, 94 insertions(+), 44 deletions(-)
>>
>> diff --git a/Documentation/PCI/pci-error-recovery.rst b/Documentation/PCI/pci-error-recovery.rst
>> index 84ceebb08cac..830c8af5838b 100644
>> --- a/Documentation/PCI/pci-error-recovery.rst
>> +++ b/Documentation/PCI/pci-error-recovery.rst
>> @@ -115,7 +115,7 @@ The actual steps taken by a platform to recover from a PCI error
>> event will be platform-dependent, but will follow the general
>> sequence described below.
>>
>> -STEP 0: Error Event
>> +STEP 0: Error Event: ERR_NONFATAL
>> -------------------
>> A PCI bus error is detected by the PCI hardware. On powerpc, the slot
>> is isolated, in that all I/O is blocked: all reads return 0xffffffff,
>> @@ -160,10 +160,10 @@ particular, if the platform doesn't isolate slots), and recovery
>> proceeds to STEP 2 (MMIO Enable).
>>
>> If any driver requested a slot reset (by returning PCI_ERS_RESULT_NEED_RESET),
>> -then recovery proceeds to STEP 4 (Slot Reset).
>> +then recovery proceeds to STEP 3 (Slot Reset).
>>
>> If the platform is unable to recover the slot, the next step
>> -is STEP 6 (Permanent Failure).
>> +is STEP 5 (Permanent Failure).
>>
>> .. note::
>>
>> @@ -198,7 +198,7 @@ reset or some such, but not restart operations. This callback is made if
>> all drivers on a segment agree that they can try to recover and if no automatic
>> link reset was performed by the HW. If the platform can't just re-enable IOs
>> without a slot reset or a link reset, it will not call this callback, and
>> -instead will have gone directly to STEP 3 (Link Reset) or STEP 4 (Slot Reset)
>> +instead will have gone directly to STEP 3 (Slot Reset)
>>
>> .. note::
>>
>> @@ -233,18 +233,12 @@ The driver should return one of the following result codes:
>>
>> The next step taken depends on the results returned by the drivers.
>> If all drivers returned PCI_ERS_RESULT_RECOVERED, then the platform
>> -proceeds to either STEP3 (Link Reset) or to STEP 5 (Resume Operations).
>> +proceeds to STEP 4 (Resume Operations).
>>
>> If any driver returned PCI_ERS_RESULT_NEED_RESET, then the platform
>> -proceeds to STEP 4 (Slot Reset)
>> +proceeds to STEP 3 (Slot Reset)
>>
>> -STEP 3: Link Reset
>> -------------------
>> -The platform resets the link. This is a PCI-Express specific step
>> -and is done whenever a fatal error has been detected that can be
>> -"solved" by resetting the link.
>> -
>> -STEP 4: Slot Reset
>> +STEP 3: Slot Reset
>> ------------------
>>
>> In response to a return value of PCI_ERS_RESULT_NEED_RESET, the
>> @@ -322,7 +316,7 @@ PCI card types::
>> + pdev->needs_freset = 1;
>> +
>>
>> -Platform proceeds either to STEP 5 (Resume Operations) or STEP 6 (Permanent
>> +Platform proceeds either to STEP 4 (Resume Operations) or STEP 5 (Permanent
>> Failure).
>>
>> .. note::
>> @@ -332,7 +326,7 @@ Failure).
>> However, it probably should.
>>
>>
>> -STEP 5: Resume Operations
>> +STEP 4: Resume Operations
>> -------------------------
>> The platform will call the resume() callback on all affected device
>> drivers if all drivers on the segment have returned
>> @@ -344,7 +338,7 @@ a result code.
>> At this point, if a new error happens, the platform will restart
>> a new error recovery sequence.
>>
>> -STEP 6: Permanent Failure
>> +STEP 5: Permanent Failure
>> -------------------------
>> A "permanent failure" has occurred, and the platform cannot recover
>> the device. The platform will call error_detected() with a
>> @@ -367,6 +361,27 @@ errors. See the discussion in powerpc/eeh-pci-error-recovery.txt
>> for additional detail on real-life experience of the causes of
>> software errors.
>>
>> +STEP 0: Error Event: ERR_FATAL
>> +--------------------
>> +PCI bus error is detected by the PCI hardware. On powerpc, the slot is
>> +isolated, in that all I/O is blocked: all reads return 0xffffffff, all
>> +writes are ignored.
>> +
>> +STEP 1: Remove devices
>> +---------------------
>> +Platform removes the devices depending on the error agent, it could be
>> +this port for all subordinates or upstream component (likely downstream
>> +port)
>> +
>> +STEP 2: Reset link
>> +---------------------
>> +The platform resets the link. This is a PCI-Express specific step and is
>> +done whenever a fatal error has been detected that can be "solved" by
>> +resetting the link.
>> +
>> +STEP 3: Re-enumerate the devices
>> +---------------------
>> +Initiates the re-enumeration.
>>
>> Conclusion; General Remarks
>> ---------------------------
>> diff --git a/Documentation/PCI/pcieaer-howto.rst b/Documentation/PCI/pcieaer-howto.rst
>> index 0b36b9ebfa4b..9528cfd9449b 100644
>> --- a/Documentation/PCI/pcieaer-howto.rst
>> +++ b/Documentation/PCI/pcieaer-howto.rst
>> @@ -206,7 +206,7 @@ error_detected(dev, pci_channel_io_frozen) to all drivers within
>> a hierarchy in question. Then, performing link reset at upstream is
>> necessary. As different kinds of devices might use different approaches
>> to reset link, AER port service driver is required to provide the
>> -function to reset link via callback parameter of pcie_do_recovery()
>> +function to reset link via callback parameter of pcie_do_fatal_recovery()
>> function. If reset_link is not NULL, recovery function will use it
>> to reset the link. If error_detected returns PCI_ERS_RESULT_CAN_RECOVER
>> and reset_link returns PCI_ERS_RESULT_RECOVERED, the error handling goes
>> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
>> index fa12f7cbc1a0..b3e1571107b5 100644
>> --- a/drivers/pci/pci.h
>> +++ b/drivers/pci/pci.h
>> @@ -555,8 +555,9 @@ static inline int pci_dev_specific_disable_acs_redir(struct pci_dev *dev)
>> #endif
>>
>> /* PCI error reporting and recovery */
>> -pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>> - pci_channel_state_t state,
>> +pci_ers_result_t pcie_do_nonfatal_recovery(struct pci_dev *dev);
>> +
>> +pci_ers_result_t pcie_do_fatal_recovery(struct pci_dev *dev,
>> pci_ers_result_t (*reset_link)(struct pci_dev *pdev));
>>
>> bool pcie_wait_for_link(struct pci_dev *pdev, bool active);
>> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
>> index 65dff5f3457a..f3e70bb9b30d 100644
>> --- a/drivers/pci/pcie/aer.c
>> +++ b/drivers/pci/pcie/aer.c
>> @@ -947,9 +947,9 @@ static void handle_error_source(struct pci_dev *dev, struct aer_err_info *info)
>> if (pcie_aer_is_native(dev))
>> pcie_clear_device_status(dev);
>> } else if (info->severity == AER_NONFATAL)
>> - pcie_do_recovery(dev, pci_channel_io_normal, aer_root_reset);
>> + pcie_do_nonfatal_recovery(dev);
>> else if (info->severity == AER_FATAL)
>> - pcie_do_recovery(dev, pci_channel_io_frozen, aer_root_reset);
>> + pcie_do_fatal_recovery(dev, aer_root_reset);
>> pci_dev_put(dev);
>> }
>>
>> @@ -985,11 +985,9 @@ static void aer_recover_work_func(struct work_struct *work)
>> }
>> cper_print_aer(pdev, entry.severity, entry.regs);
>> if (entry.severity == AER_NONFATAL)
>> - pcie_do_recovery(pdev, pci_channel_io_normal,
>> - aer_root_reset);
>> + pcie_do_nonfatal_recovery(pdev);
>> else if (entry.severity == AER_FATAL)
>> - pcie_do_recovery(pdev, pci_channel_io_frozen,
>> - aer_root_reset);
>> + pcie_do_fatal_recovery(pdev, aer_root_reset);
>> pci_dev_put(pdev);
>> }
>> }
>> diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
>> index daa9a4153776..74e7d1da3cf0 100644
>> --- a/drivers/pci/pcie/dpc.c
>> +++ b/drivers/pci/pcie/dpc.c
>> @@ -233,7 +233,7 @@ static irqreturn_t dpc_handler(int irq, void *context)
>> dpc_process_error(pdev);
>>
>> /* We configure DPC so it only triggers on ERR_FATAL */
>> - pcie_do_recovery(pdev, pci_channel_io_frozen, dpc_reset_link);
>> + pcie_do_fatal_recovery(pdev, dpc_reset_link);
>>
>> return IRQ_HANDLED;
>> }
>> diff --git a/drivers/pci/pcie/edr.c b/drivers/pci/pcie/edr.c
>> index a6b9b479b97a..87379bc566f6 100644
>> --- a/drivers/pci/pcie/edr.c
>> +++ b/drivers/pci/pcie/edr.c
>> @@ -183,7 +183,7 @@ static void edr_handle_event(acpi_handle handle, u32 event, void *data)
>> * or ERR_NONFATAL, since the link is already down, use the FATAL
>> * error recovery path for both cases.
>> */
>> - estate = pcie_do_recovery(edev, pci_channel_io_frozen, dpc_reset_link);
>> + estate = pcie_do_fatal_recovery(edev, dpc_reset_link);
>>
>> send_ost:
>>
>> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
>> index 315a4d559c4c..fa50366a9632 100644
>> --- a/drivers/pci/pcie/err.c
>> +++ b/drivers/pci/pcie/err.c
>> @@ -79,11 +79,6 @@ static int report_error_detected(struct pci_dev *dev,
>> return 0;
>> }
>>
>> -static int report_frozen_detected(struct pci_dev *dev, void *data)
>> -{
>> - return report_error_detected(dev, pci_channel_io_frozen, data);
>> -}
>> -
>> static int report_normal_detected(struct pci_dev *dev, void *data)
>> {
>> return report_error_detected(dev, pci_channel_io_normal, data);
>> @@ -146,9 +141,59 @@ static int report_resume(struct pci_dev *dev, void *data)
>> return 0;
>> }
>>
>> -pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>> - pci_channel_state_t state,
>> +pci_ers_result_t pcie_do_fatal_recovery(struct pci_dev *dev,
>> pci_ers_result_t (*reset_link)(struct pci_dev *pdev))
>> +{
>> + struct pci_dev *udev;
>> + struct pci_bus *parent;
>> + struct pci_dev *pdev, *temp;
>> + pci_ers_result_t result;
>> +
>> + if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE)
>> + udev = dev;
>> + else
>> + udev = dev->bus->self;
>> +
>> + parent = udev->subordinate;
>> + pci_walk_bus(parent, pci_dev_set_disconnected, NULL);
>> +
>> + pci_lock_rescan_remove();
>> + pci_dev_get(dev);
>> + list_for_each_entry_safe_reverse(pdev, temp, &parent->devices,
>> + bus_list) {
>> + pci_stop_and_remove_bus_device(pdev);
>
> Again , pciehp driver wouldn't naturally ignore the DLLSC/PDC event,
> or because you do
> pci_stop_and_remove_bus_device(pdev) here, pciehp driver wouldn't do
> pcie_disable_slot()
> anymore, when DPC driver get its interrupt and run into here, pciehp
> driver also gets DLLSC
> /PDC and may run into SUPPRISE_REMOVAL first. so there would be duplicated
> pci_stop_and_remove_bus_device(pdev);

If you check the implementation of pci_stop_and_remove_bus_device(), all it
does is to go over the list of sub-devices and bus device, and then do pci_stop_dev() and
pci_destroy_dev() operations. My point is, once the device is stopped or removed then
in other thread which executes pci_stop_and_remove_bus_device(), the same device will
not be present. And hence we are not repeating the core operation. Ofcourse there are
still some duplication (like DLLSC/PDC event handling). But I am not trying to solve
that problem here.

I am just making error recovery handler own this functionality to solve,

1. recovery problem of non-hotplug capapble devices.
2. remove dependency on hotplug handler for handline remove and rescan functionality.
3. Make pcie_do_recovery() less complex.

>
> Don't say it would naturally be okay. check it.
>
>> + }
>> +
>> + result = reset_link(udev);
>> +
>> + if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
>> + /*
>> + * If the error is reported by a bridge, we think this error
>> + * is related to the downstream link of the bridge, so we
>> + * do error recovery on all subordinates of the bridge instead
>> + * of the bridge and clear the error status of the bridge.
>> + */
>> + pci_aer_clear_fatal_status(dev);
>> + if (pcie_aer_is_native(dev))
>> + pcie_clear_device_status(dev);
>> + }
>> +
>> + if (result == PCI_ERS_RESULT_RECOVERED) {
>> + if (pcie_wait_for_link(udev, true))
>> + pci_rescan_bus(udev->bus);
> So does to this pci_rescan_bus(udev->bus);
> You said you won't rely on pciehp handler, but how do you eliminate the
> handler's duplicated actions.
>
> Thanks,
> Ethan
>> + pci_info(dev, "Device recovery from fatal error successful\n");
>> + } else {
>> + pci_uevent_ers(dev, PCI_ERS_RESULT_DISCONNECT);
>> + pci_info(dev, "Device recovery from fatal error failed\n");
>> + }
>> +
>> + pci_dev_put(dev);
>> + pci_unlock_rescan_remove();
>> +
>> + return result;
>> +}
>> +
>> +pci_ers_result_t pcie_do_nonfatal_recovery(struct pci_dev *dev)
>> {
>> pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
>> struct pci_bus *bus;
>> @@ -164,16 +209,7 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>> bus = dev->subordinate;
>>
>> 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) {
>> - pci_warn(dev, "link reset failed\n");
>> - goto failed;
>> - }
>> - } else {
>> - pci_walk_bus(bus, report_normal_detected, &status);
>> - }
>> + pci_walk_bus(bus, report_normal_detected, &status);
>>
>> if (status == PCI_ERS_RESULT_CAN_RECOVER) {
>> status = PCI_ERS_RESULT_RECOVERED;
>> --
>> 2.17.1
>>

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer