linux-kernel - Re: [PATCH v11 1/8] PCI/ERR: Update error status after reset

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Date:   Wed, 8 Jan 2020 16:14:09 -0800
From:   Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        ashok.raj@...el.com, keith.busch@...el.com
Subject: Re: [PATCH v11 1/8] PCI/ERR: Update error status after reset_link()

Hi Bjorn,

Thanks for the comments.

On 1/3/20 6:54 PM, Bjorn Helgaas wrote:
> On Fri, Jan 03, 2020 at 05:03:03PM -0800, Kuppuswamy Sathyanarayanan wrote:
>> On 1/3/20 4:34 PM, Bjorn Helgaas wrote:
>>> On Thu, Dec 26, 2019 at 04:39:07PM -0800, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
>>>> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
>>>>
>>>> Commit bdb5ac85777d ("PCI/ERR: Handle fatal error recovery") uses
>>>> reset_link() to recover from fatal errors. But, if the reset is
>>>> successful there is no need to continue the rest of the error recovery
>>>> checks. Also, during fatal error recovery, if the initial value of error
>>>> status is PCI_ERS_RESULT_DISCONNECT or PCI_ERS_RESULT_NO_AER_DRIVER then
>>>> even after successful recovery (using reset_link()) pcie_do_recovery()
>>>> will report the recovery result as failure. So update the status of
>>>> error after reset_link().
>>> I like the part about updating "status" with the result of
>>> reset_link(), and I split that into its own patch because it
>>> seems like a fix that *can* be separated.
>>>
>>> But I'm not convinced that we should skip the ->slot_reset()
>>> callbacks if the reset_link() was successful.
>> If reset_link() call is successful then the result value will be
>> "PCI_ERS_RESULT_RECOVERED". So even if you proceed with
>> rest of the code, slot_reset() will never get called right ?
> The current code:
>
>          if (state == pci_channel_io_frozen &&
>              reset_link(dev, service) != PCI_ERS_RESULT_RECOVERED)
>                  goto failed;
>          ...
>          if (status == PCI_ERS_RESULT_NEED_RESET) {
>                  status = PCI_ERS_RESULT_RECOVERED;
>                  pci_walk_bus(bus, report_slot_reset, &status);
>
> doesn't save the result of reset_link(), so if status was
> PCI_ERS_RESULT_NEED_RESET and the reset succeeds, we will call
> ->slot_reset().
>
> After your patch, if "state == pci_channel_io_frozen", we *never* call
> ->slot_reset().
>
> Do you think that matches pci-error-recovery.rst?  It doesn't seem
> like it to me, but perhaps I haven't read it closely enough.
Documentation does not have clear details on what to do with return
value of reset_link() ( step 3). But IMO, if step 3 recovers the device and
returns PCI_ERS_RESULT_RECOVERED then there is no need to proceed
to slot reset (step 4). May be we should update the Documentation ?

Keith,
You have any comments ?
>
>>> According to
>>> Documentation/PCI/pci-error-recovery.rst, we should call
>>> ->slot_reset() after completion of the reset.
>>>
>>> For example, rsxx_err_handler implements ->slot_reset(), but
>>> not ->resume().  If we reset the device, we'll claim success and
>>> return, but we won't call rsxx_slot_reset(), which does a bunch
>>> of important-looking recovery stuff.
>>>
>>> If pci-error-recovery.rst is wrong, we should fix that (after
>>> auditing all the drivers to make sure they match).
>>>
>>>> Fixes: bdb5ac85777d ("PCI/ERR: Handle fatal error recovery")
>>>> Cc: Ashok Raj <ashok.raj@...el.com>
>>>> Cc: Keith Busch <keith.busch@...el.com>
>>>> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
>>>> Acked-by: Keith Busch <keith.busch@...el.com>
>>>> ---
>>>>    drivers/pci/pcie/err.c | 10 +++++++---
>>>>    1 file changed, 7 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
>>>> index b0e6048a9208..53cd9200ec2c 100644
>>>> --- a/drivers/pci/pcie/err.c
>>>> +++ b/drivers/pci/pcie/err.c
>>>> @@ -204,9 +204,12 @@ void pcie_do_recovery(struct pci_dev *dev, enum pci_channel_state state,
>>>>    	else
>>>>    		pci_walk_bus(bus, report_normal_detected, &status);
>>>> -	if (state == pci_channel_io_frozen &&
>>>> -	    reset_link(dev, service) != PCI_ERS_RESULT_RECOVERED)
>>>> -		goto failed;
>>>> +	if (state == pci_channel_io_frozen) {
>>>> +		status = reset_link(dev, service);
>>>> +		if (status != PCI_ERS_RESULT_RECOVERED)
>>>> +			goto failed;
>>>> +		goto done;
>>>> +	}
>>>>    	if (status == PCI_ERS_RESULT_CAN_RECOVER) {
>>>>    		status = PCI_ERS_RESULT_RECOVERED;
>>>> @@ -228,6 +231,7 @@ void pcie_do_recovery(struct pci_dev *dev, enum pci_channel_state state,
>>>>    	if (status != PCI_ERS_RESULT_RECOVERED)
>>>>    		goto failed;
>>>> +done:
>>>>    	pci_dbg(dev, "broadcast resume message\n");
>>>>    	pci_walk_bus(bus, report_resume, &status);
>>>> -- 
>>>> 2.21.0
>>>>
>> -- 
>> Sathyanarayanan Kuppuswamy
>> Linux kernel developer
>>
-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer