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Message-ID: <26CA7DEF-4967-4E41-9998-A02178439A00@intel.com>
Date: Mon, 30 Nov 2020 19:54:37 +0000
From: "Kelley, Sean V" <sean.v.kelley@...el.com>
To: Bjorn Helgaas <helgaas@...nel.org>
CC: "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
"xerces.zhao@...il.com" <xerces.zhao@...il.com>,
"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
"Raj, Ashok" <ashok.raj@...el.com>,
"Luck, Tony" <tony.luck@...el.com>,
"Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@...el.com>,
"Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>,
Linux PCI <linux-pci@...r.kernel.org>,
"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 10/15] PCI/ERR: Limit AER resets in pcie_do_recovery()
Hi Bjorn,
Was away briefly for the holidays, comments below:
> On Nov 24, 2020, at 9:17 AM, Bjorn Helgaas <helgaas@...nel.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@...nel.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@...el.com>
>>>> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
>>>> Acked-by: Jonathan Cameron <Jonathan.Cameron@...wei.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
>>
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