linux-kernel - Re: [PATCH] PCI: pciehp: Fix system hang on resume after hot-unplug during suspend

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Message-ID: <3354e37e-c48a-4696-a074-2df9e625fc0c@linux.intel.com>
Date: Wed, 23 Oct 2024 12:23:54 +0800
From: Ethan Zhao <haifeng.zhao@...ux.intel.com>
To: AceLan Kao <acelan.kao@...onical.com>, Lukas Wunner <lukas@...ner.de>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: pciehp: Fix system hang on resume after hot-unplug
 during suspend

On 10/17/2024 10:40 AM, AceLan Kao wrote:
> AceLan Kao <acelan.kao@...onical.com> 於 2024年10月7日 週一 下午12:34寫道：
>> Lukas Wunner <lukas@...ner.de> 於 2024年10月1日 週二 下午7:03寫道：
>>> On Tue, Oct 01, 2024 at 01:02:46PM +0200, Lukas Wunner wrote:
>>>> On Mon, Sep 30, 2024 at 09:31:53AM +0800, AceLan Kao wrote:
>>>>> Lukas Wunner <lukas@...ner.de> 2024 9 28 8:51:
>>>>>> -       if (pci_get_dsn(pdev) != ctrl->dsn)
>>>>>> +       dsn = pci_get_dsn(pdev);
>>>>>> +       if (!PCI_POSSIBLE_ERROR(dsn) &&
>>>>>> +           dsn != ctrl->dsn)
>>>>>>                  return true;
>>>>> In my case, the pciehp_device_replaced() returns true from this final check.
>>>>> And these are the values I got
>>>>> dsn = 0x00000000, ctrl->dsn = 0x7800AA00
>>>>> dsn = 0x00000000, ctrl->dsn = 0x21B7D000
>>>> Ah because pci_get_dsn() returns 0 if the device is gone.
>>>> Below is a modified patch which returns false in that case.
>>> Sorry, forgot to include the patch:
>>>
>>> -- >8 --
>>>
>>> diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
>>> index ff458e6..957c320 100644
>>> --- a/drivers/pci/hotplug/pciehp_core.c
>>> +++ b/drivers/pci/hotplug/pciehp_core.c
>>> @@ -287,24 +287,32 @@ static int pciehp_suspend(struct pcie_device *dev)
>>>   static bool pciehp_device_replaced(struct controller *ctrl)
>>>   {
>>>          struct pci_dev *pdev __free(pci_dev_put);
>>> +       u64 dsn;
>>>          u32 reg;
>>>
>>>          pdev = pci_get_slot(ctrl->pcie->port->subordinate, PCI_DEVFN(0, 0));
>>>          if (!pdev)
>>> +               return false;
>>> +
>>> +       if (pci_read_config_dword(pdev, PCI_VENDOR_ID, &reg) == 0 &&
>>> +           !PCI_POSSIBLE_ERROR(reg) &&
>>> +           reg != (pdev->vendor | (pdev->device << 16)))
>>>                  return true;
>>>
>>> -       if (pci_read_config_dword(pdev, PCI_VENDOR_ID, &reg) ||
>>> -           reg != (pdev->vendor | (pdev->device << 16)) ||
>>> -           pci_read_config_dword(pdev, PCI_CLASS_REVISION, &reg) ||
>>> +       if (pci_read_config_dword(pdev, PCI_CLASS_REVISION, &reg) == 0 &&
>>> +           !PCI_POSSIBLE_ERROR(reg) &&
>>>              reg != (pdev->revision | (pdev->class << 8)))
>>>                  return true;
>>>
>>>          if (pdev->hdr_type == PCI_HEADER_TYPE_NORMAL &&
>>> -           (pci_read_config_dword(pdev, PCI_SUBSYSTEM_VENDOR_ID, &reg) ||
>>> -            reg != (pdev->subsystem_vendor | (pdev->subsystem_device << 16))))
>>> +           pci_read_config_dword(pdev, PCI_SUBSYSTEM_VENDOR_ID, &reg) == 0 &&
>>> +           !PCI_POSSIBLE_ERROR(reg) &&
>>> +           reg != (pdev->subsystem_vendor | (pdev->subsystem_device << 16)))
>>>                  return true;
>>>
>>> -       if (pci_get_dsn(pdev) != ctrl->dsn)
>>> +       if ((dsn = pci_get_dsn(pdev)) &&
>>> +           !PCI_POSSIBLE_ERROR(dsn) &&
>>> +           dsn != ctrl->dsn)
>>>                  return true;
>>>
>>>          return false;
>> Hi Lukas,
>>
>> Sorry for the late reply, just encountered a strong typhoon in my area
>> last week and can't check this in our lab.
>>
>> The patched pciehp_device_replaced() returns false at the end of the
>> function in my case.
>> Unplug the dock which is connected with a tbt storage won't be
>> considered as a replacement.
>>
>> But when I tried to replace the dock with the tbt storage during
>> suspend, it still returned false at the end of the function like
>> unplugged.
>>
>> BTW, it's a new model, so I think the ICM is used. And the reg is
>> 0xffffffff when unplugged.
> Hi Lukas,
>
> PCI_POSSIBLE_ERROR() always returns true no matter the device is
> replaced or unplugged
> It seems difficult to distinguish between when a device is replaced
> and when it's unplugged.

If DSN (Device Serial Number) is not optional extended capability, then
we could use it as a tag to know if the device is replaced or unplugged.

So it would be better to have something like DSN but not optional in spec.

Thanks,
Ethan

>
> Do you have any ideas to fix the issue?
> This issue is severe to me, because the system hangs almost everytime
> when daisy chain tbt devices are unplugged when suspended.
> Thanks.
>