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SubjectRe: [PATCH v2 1/6] PCI/AER: Take severity mask into account while clearing error bits
On 2018-07-18 03:06, Bjorn Helgaas wrote:
> On Tue, Jul 17, 2018 at 02:03:29PM -0500, Bjorn Helgaas wrote:
>> Hi Oza,
>>
>> Thanks for doing this!
>>
>> On Fri, Jun 22, 2018 at 05:58:09AM -0400, Oza Pawandeep wrote:
>> > pci_cleanup_aer_uncorrect_error_status() is called by different slot_reset
>> > callbacks in case of ERR_NONFATAL.
>>
>> IIRC, the current strategy is:
>>
>> ERR_COR: log only
>> ERR_NONFATAL: call driver callbacks (pci_error_handlers)
>> ERR_FATAL: remove device and re-enumerate
>>
>> So these slot_reset callbacks are only used for ERR_NONFATAL, which
>> are all uncorrectable errors, of course.
>>
>> This patch makes it so that when the slot_reset callbacks call
>> pci_cleanup_aer_uncorrect_error_status(), we only clear the
>> bits set by ERR_NONFATAL events (this is determined by
>> PCI_ERR_UNCOR_SEVER).
>>
>> That makes good sense to me. All these status bits are RW1CS, so they
>> will be preserved across a reset but will be cleared when we
>> re-enumerate, in this path:
>>
>> pci_init_capabilities
>> pci_aer_init
>> pci_cleanup_aer_error_status_regs
>> # clear all PCI_ERR_UNCOR_STATUS and PCI_ERR_COR_STATUS bits
>>
>> > AER uncorrectable error status should take severity into account in order
>> > to clear the bits, so that ERR_NONFATAL path does not clear the bit which
>> > are marked with severity fatal.
>>
>> Two comments:
>>
>> 1) Can you split this into two patches, one that changes
>> pci_cleanup_aer_uncorrect_error_status() so it looks like the error
>> clearing code in aer_error_resume(), and a second that factors out the
>> duplicate code?
>>
>> 2) Maybe use "sev" or "sever" instead of "mask" for the local
>> variable, since there is also a separate PCI_ERR_UNCOR_MASK register,
>> which is not involved here.
>
> Let me back up a little here: I'm not asking you to do the things
> below here. They're just possible future things, so we can think
> about them after this series. And the things above are things I can
> easily do myself. So no action required from you, unless you think
> I'm on the wrong track :)

I agree with your points, and have taken them into account for future
series reference as well.

what about PATCH-2 of this series ?
that clears ERR_FATAL bits, but as you said, during re-enumeration
pci_init_capabilities
pci_aer_init
pci_cleanup_aer_error_status_regs
# clear all PCI_ERR_UNCOR_STATUS and PCI_ERR_COR_STATUS bits

but that should clear the ERR_FATAL of the devices beneath.

PATCH2: we are doing it for BRIDGE where we think where ERR_FATAL was
reported by bridge and the problem is with downstream link.
if ((service == PCIE_PORT_SERVICE_AER) &&
(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_cleanup_aer_uncorrect_error_status(dev);
}


so overall, I think all the patches are required, if you have comments
please let me know.
so far I see that, no action is required from me.

>
>> 3) The "pci_cleanup_aer_uncorrect_error_status()" name no longer
>> really describes what this does. Something like
>> "pci_aer_clear_nonfatal_status()" would be more descriptive. But I
>> see you have a subsequent patch (which I haven't looked at yet) that
>> is related to this.
>>
>> 4) I don't think the driver slot_reset callbacks should be responsible
>> for clearing these AER status bits. Can we clear them somewhere in
>> the pcie_do_nonfatal_recovery() path and remove these calls from the
>> drivers?
>>
>> 5) In principle, we should only read PCI_ERR_UNCOR_STATUS *once* per
>> device when handling an error. We currently read it three times:
>>
>> aer_isr
>> aer_isr_one_error
>> find_source_device
>> find_device_iter
>> is_error_source
>> read PCI_ERR_UNCOR_STATUS # 1
>> aer_process_err_devices
>> get_device_error_info(e_info->dev[i])
>> read PCI_ERR_UNCOR_STATUS # 2
>> handle_error_source
>> pcie_do_nonfatal_recovery
>> ...
>> report_slot_reset
>> driver->err_handler->slot_reset
>> pci_cleanup_aer_uncorrect_error_status
>> read PCI_ERR_UNCOR_STATUS # 3
>>
>> OK, that was more than two comments :)

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