Re: [PATCH v12 10/15] PCI/ERR: Limit AER resets in pcie_do_recovery()

From: "Kelley, Sean V" <sean.v.kelley@intel.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: "bhelgaas@google.com" <bhelgaas@google.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	"xerces.zhao@gmail.com" <xerces.zhao@gmail.com>,
	"Wysocki, Rafael J" <rafael.j.wysocki@intel.com>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	"Luck, Tony" <tony.luck@intel.com>,
	"Kuppuswamy,
	Sathyanarayanan" <sathyanarayanan.kuppuswamy@intel.com>,
	"Zhuo, Qiuxu" <qiuxu.zhuo@intel.com>,
	Linux PCI <linux-pci@vger.kernel.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v12 10/15] PCI/ERR: Limit AER resets in pcie_do_recovery()
Date: Mon, 30 Nov 2020 19:54:37 +0000	[thread overview]
Message-ID: <26CA7DEF-4967-4E41-9998-A02178439A00@intel.com> (raw)
In-Reply-To: <20201124171746.GA565099@bjorn-Precision-5520>

Hi Bjorn,

Was away briefly for the holidays, comments below:

> On Nov 24, 2020, at 9:17 AM, Bjorn Helgaas <helgaas@kernel.org> wrote:
> 
> On Mon, Nov 23, 2020 at 11:57:35PM +0000, Kelley, Sean V wrote:
>>> On Nov 23, 2020, at 3:28 PM, Bjorn Helgaas <helgaas@kernel.org> wrote:
>>> On Fri, Nov 20, 2020 at 04:10:31PM -0800, Sean V Kelley wrote:
>>>> In some cases a bridge may not exist as the hardware controlling may be
>>>> handled only by firmware and so is not visible to the OS. This scenario is
>>>> also possible in future use cases involving non-native use of RCECs by
>>>> firmware.
>>>> 
>>>> Explicitly apply conditional logic around these resets by limiting them to
>>>> Root Ports and Downstream Ports.
>>> 
>>> Can you help me understand this?  The subject says "Limit AER resets"
>>> and here you say "limit them to RPs and DPs", but it's not completely
>>> obvious how the resets are being limited, i.e., the patch doesn't add
>>> anything like:
>>> 
>>> +  if (type == PCI_EXP_TYPE_ROOT_PORT ||
>>> +      type == PCI_EXP_TYPE_DOWNSTREAM)
>>>     reset_subordinates(bridge);
>>> 
>>> It *does* add checks around pcie_clear_device_status(), but that also
>>> includes RC_EC.  And that's not a reset, so I don't think that's
>>> explicitly mentioned in the commit log.
>> 
>> The subject should have referred to the clearing of the device status rather than resets.
>> It originally came from this simpler patch in which I made use of reset instead of clear:
>> 
>> https://lore.kernel.org/linux-pci/20201002184735.1229220-8-seanvk.dev@oregontracks.org/
>> 
>> So a rephrase of clearing in place of resets would be more appropriate.
>> 
>> Then we added the notion of bridges…below
>> 
>>> 
>>> Also see the question below.
>>> 
>>>> Link: https://lore.kernel.org/r/20201002184735.1229220-8-seanvk.dev@oregontracks.org
>>>> Signed-off-by: Sean V Kelley <sean.v.kelley@intel.com>
>>>> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
>>>> Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>>>> ---
>>>> drivers/pci/pcie/err.c | 31 +++++++++++++++++++++++++------
>>>> 1 file changed, 25 insertions(+), 6 deletions(-)
>>>> 
>>>> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
>>>> index 8b53aecdb43d..7883c9791562 100644
>>>> --- a/drivers/pci/pcie/err.c
>>>> +++ b/drivers/pci/pcie/err.c
>>>> @@ -148,13 +148,17 @@ static int report_resume(struct pci_dev *dev, void *data)
>>>> 
>>>> /**
>>>> * pci_walk_bridge - walk bridges potentially AER affected
>>>> - * @bridge:	bridge which may be a Port
>>>> + * @bridge:	bridge which may be a Port, an RCEC with associated RCiEPs,
>>>> + *		or an RCiEP associated with an RCEC
>>>> * @cb:		callback to be called for each device found
>>>> * @userdata:	arbitrary pointer to be passed to callback
>>>> *
>>>> * If the device provided is a bridge, walk the subordinate bus, including
>>>> * any bridged devices on buses under this bus.  Call the provided callback
>>>> * on each device found.
>>>> + *
>>>> + * If the device provided has no subordinate bus, call the callback on the
>>>> + * device itself.
>>>> */
>>>> static void pci_walk_bridge(struct pci_dev *bridge,
>>>> 			    int (*cb)(struct pci_dev *, void *),
>>>> @@ -162,6 +166,8 @@ static void pci_walk_bridge(struct pci_dev *bridge,
>>>> {
>>>> 	if (bridge->subordinate)
>>>> 		pci_walk_bus(bridge->subordinate, cb, userdata);
>>>> +	else
>>>> +		cb(bridge, userdata);
>>>> }
>>>> 
>>>> pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>>>> @@ -174,10 +180,13 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>>>> 
>>>> 	/*
>>>> 	 * Error recovery runs on all subordinates of the bridge.  If the
>>>> -	 * bridge detected the error, it is cleared at the end.
>>>> +	 * bridge detected the error, it is cleared at the end.  For RCiEPs
>>>> +	 * we should reset just the RCiEP itself.
>>>> 	 */
>>>> 	if (type == PCI_EXP_TYPE_ROOT_PORT ||
>>>> -	    type == PCI_EXP_TYPE_DOWNSTREAM)
>>>> +	    type == PCI_EXP_TYPE_DOWNSTREAM ||
>>>> +	    type == PCI_EXP_TYPE_RC_EC ||
>>>> +	    type == PCI_EXP_TYPE_RC_END)
>>>> 		bridge = dev;
>>>> 	else
>>>> 		bridge = pci_upstream_bridge(dev);
>>>> @@ -185,6 +194,12 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>>>> 	pci_dbg(bridge, "broadcast error_detected message\n");
>>>> 	if (state == pci_channel_io_frozen) {
>>>> 		pci_walk_bridge(bridge, report_frozen_detected, &status);
>>>> +		if (type == PCI_EXP_TYPE_RC_END) {
>>>> +			pci_warn(dev, "subordinate device reset not possible for RCiEP\n");
>>>> +			status = PCI_ERS_RESULT_NONE;
>>>> +			goto failed;
>>>> +		}
>>>> +
>>>> 		status = reset_subordinates(bridge);
>>>> 		if (status != PCI_ERS_RESULT_RECOVERED) {
>>>> 			pci_warn(bridge, "subordinate device reset failed\n");
>>>> @@ -217,9 +232,13 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>>>> 	pci_dbg(bridge, "broadcast resume message\n");
>>>> 	pci_walk_bridge(bridge, report_resume, &status);
>>>> 
>>>> -	if (pcie_aer_is_native(bridge))
>>>> -		pcie_clear_device_status(bridge);
>>>> -	pci_aer_clear_nonfatal_status(bridge);
>>>> +	if (type == PCI_EXP_TYPE_ROOT_PORT ||
>>>> +	    type == PCI_EXP_TYPE_DOWNSTREAM ||
>>>> +	    type == PCI_EXP_TYPE_RC_EC) {
>>>> +		if (pcie_aer_is_native(bridge))
>>>> +			pcie_clear_device_status(bridge);
>>>> +		pci_aer_clear_nonfatal_status(bridge);
>>> 
>>> This is hard to understand because "type" is from "dev", but "bridge"
>>> is not necessarily the same device.  Should it be this?
>>> 
>>> type = pci_pcie_type(bridge);
>>> if (type == PCI_EXP_TYPE_ROOT_PORT ||
>>>     ...)
>> 
>> Correct, it would be better if the type was based on the ‘bridge’.
> 
> OK.  This is similar to
> https://lore.kernel.org/linux-pci/20201002184735.1229220-8-seanvk.dev@oregontracks.org/,
> which you cited above except for the bridge/dev question and the
> addition here of RC_EC.
> 
> I tried to split that back into its own patch and started with the
> commit message from that patch.  But I got stuck on the commit
> message.  I got as far as:
> 
>  In some cases an error may be reported by a device not visible to
>  the OS, e.g., if firmware manages the device and passes error
>  information to the OS via ACPI APEI.
> 
> But I still can't quite connect that to the patch.  "bridge" is
> clearly a device visible to Linux.

> 
> I guess we're trying to assert that if "bridge" is not a Root Port,
> Downstream Port, or RCEC, we shouldn't clear the error status because 
> the error came from a device Linux doesn't know about.  But I think
> "bridge" is *always* either a Root Port or a Downstream Port:

That’s ultimately what we are trying to do.

> 
>  if (type == PCI_EXP_TYPE_ROOT_PORT ||
>      type == PCI_EXP_TYPE_DOWNSTREAM)
> 	  bridge = dev;
>  else
> 	  bridge = pci_upstream_bridge(dev);
> 
> pci_upstream_bridge() returns either NULL (in which case previous uses
> dereference a NULL pointer), or dev->bus->self, which is always a Root
> Port, Switch Downstream Port, or Switch Upstream Port (or NULL for the
> special case of VFs).

In the past recall we were augmenting it with bridge = dev->rcec for RC_END.
But we were able to relocate the handling in aer_root_reset().

So in this patch - we add the conditionals because RC_END is being passed in addition to RC_EC.
 
 	if (type == PCI_EXP_TYPE_ROOT_PORT ||

-	    type == PCI_EXP_TYPE_DOWNSTREAM)

+	    type == PCI_EXP_TYPE_DOWNSTREAM ||
+	    type == PCI_EXP_TYPE_RC_EC ||
+	    type == PCI_EXP_TYPE_RC_END)

 		bridge = dev;
 	else
 		bridge = pci_upstream_bridge(dev);

So we need to check for RP, DS, and RC_EC

@@ -217,9 +232,13 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,

 	pci_dbg(bridge, "broadcast resume message\n");
 	pci_walk_bridge(bridge, report_resume, &status);
 

-	if (pcie_aer_is_native(bridge))
-		pcie_clear_device_status(bridge);
-	pci_aer_clear_nonfatal_status(bridge);

+	if (type == PCI_EXP_TYPE_ROOT_PORT ||
+	    type == PCI_EXP_TYPE_DOWNSTREAM ||
+	    type == PCI_EXP_TYPE_RC_EC) {
+		if (pcie_aer_is_native(bridge))
+			pcie_clear_device_status(bridge);
+		pci_aer_clear_nonfatal_status(bridge);
+	}


Breaking out a separate patch would be unnecessary as you correctly point out that it’s only going to be an RP or DS before this patch.

Thanks,

Sean


>>>> +	}
>>>> 	pci_info(bridge, "device recovery successful\n");
>>>> 	return status;
>>>> 
>>>> -- 
>>>> 2.29.2
>> 

