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

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Date:   Thu, 9 Jan 2020 17:08:15 -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()


On 1/9/20 3:26 PM, Bjorn Helgaas wrote:
> On Wed, Jan 08, 2020 at 04:14:09PM -0800, Kuppuswamy Sathyanarayanan wrote:
>> 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?
> Are you suggesting we don't need to call a driver callback after
> resetting the device?  Note that the ->slot_reset() doesn't *perform*
> a reset; it is called *after* completion of a reset.
>
> The doc says:
>
>    ... Upon completion of slot reset, the platform will call the device
>    slot_reset() callback.
>    ...
>    This call gives drivers the chance to re-initialize the hardware
>    (re-download firmware, etc.).  At this point, the driver may assume
>    that the card is in a fresh state and is fully functional. The slot
>    is unfrozen and the driver has full access to PCI config space,
>    memory mapped I/O space and DMA. Interrupts (Legacy, MSI, or MSI-X)
>    will also be available.
Got it. Let me fix it in next version.
But, will this sequence apply for fatal error recovery (triggered from 
DPC code path) ? I think the device is removed and re-added in hotplug 
path (DLLSC transition).
>
> After we reset a device, the driver certainly needs a chance to
> reinitialize it.
>
>>>>> 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
>>
-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer