linux-kernel - Re: [PATCH] PCI/AER: don't call recovery process for correctable errors

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Message-ID: <f1e80ad1-8e08-c96c-db03-64efd4a6f245@codeaurora.org>
Date:   Tue, 7 Nov 2017 18:27:03 -0500
From:   Tyler Baicar <tbaicar@...eaurora.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     bhelgaas@...gle.com, jonathan.derrick@...el.com,
        keith.busch@...el.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI/AER: don't call recovery process for correctable
 errors

On 10/11/2017 1:09 PM, Bjorn Helgaas wrote:
> On Wed, Oct 11, 2017 at 10:37:47AM -0400, Tyler Baicar wrote:
>> On 10/2/2017 7:19 PM, Bjorn Helgaas wrote:
>>> On Mon, Aug 28, 2017 at 11:09:44AM -0600, Tyler Baicar wrote:
>>>> Correctable errors do not need any software intervention, so
>>>> avoid calling into the software recovery process for correctable
>>>> errors.
>>>>
>>>> Signed-off-by: Tyler Baicar <tbaicar@...eaurora.org>
>>>> ---
>>>>   drivers/pci/pcie/aer/aerdrv_core.c | 3 ++-
>>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/pci/pcie/aer/aerdrv_core.c b/drivers/pci/pcie/aer/aerdrv_core.c
>>>> index b1303b3..4765c11 100644
>>>> --- a/drivers/pci/pcie/aer/aerdrv_core.c
>>>> +++ b/drivers/pci/pcie/aer/aerdrv_core.c
>>>> @@ -626,7 +626,8 @@ static void aer_recover_work_func(struct work_struct *work)
>>>>   			continue;
>>>>   		}
>>>>   		cper_print_aer(pdev, entry.severity, entry.regs);
>>>> -		do_recovery(pdev, entry.severity);
>>>> +		if (entry.severity != AER_CORRECTABLE)
>>>> +			do_recovery(pdev, entry.severity);
>>> I think this is fine, and it mirrors what is done in
>>> handle_error_source().
>>>
>>> But I want to converge the APEI path and the "native" AER path, so as
>>> one tiny step in that direction, can you look into doing this test
>>> once, e.g., move the test from handle_error_source() into
>>> do_recovery(), where one test will handle both paths?
>> I've looked into this and it seems there is still going to need to
>> be two versions of this check. The native AER path goes through
>> handle_error_source() and for correctable errors requires the write
>> to PCI_ERR_COR_STATUS, but the APEI path does not require this
>> write. I could move this check to the beginning of do_recovery() so
>> it returns right away for correctable errors and remove the else
>> line in handle_error_source() so it always calls into do_recovery().
>> That doesn't seem like a very clean solution though since then there
>> are still two checks for correctable errors and now we're calling
>> into do_recovery() in both cases for nothing :)
> The PCI_ERR_COR_STATUS thing is part of what I see as the problem
> here.  IMHO, the native AER path should collect up the log registers
> (and do any acknowledgement, e.g., writing PCI_ERR_COR_STATUS)
> *before* entering the common path.
>
> In other words, the Linux code in the native part of AER should be
> functionally the same as the BIOS code that implements the APEI path.
>
> This is a bit of restructuring in the Linux AER code.  I haven't
> looked enough to know how much.  If it's impractical, it's
> impractical.  I thought this might be an opportunity for a tiny step
> in that direction, but if it's not, I guess that's OK.
Hello Bjorn,

That restructuring doesn't look trivial to do in this patch, so do you think 
this patch is
good for 4.15?

Thanks,
Tyler

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