Re: [PATCH v6 2/2] PCI/ERR: Split the fatal and non-fatal error recovery handling

Kuppuswamy, Sathyanarayanan
2020-10-15T05:53:41Z

On 10/14/20 10:05 PM, Ethan Zhao wrote:
> On Thu, Oct 15, 2020 at 11:04 AM Kuppuswamy, Sathyanarayanan
> <sathyanarayanan.kuppuswamy@linux.intel.com> wrote:
>>
>>
>>
>> On 10/14/20 6:58 PM, Ethan Zhao wrote:
>>> On Thu, Oct 15, 2020 at 1:06 AM Kuppuswamy, Sathyanarayanan
>>> <sathyanarayanan.kuppuswamy@linux.intel.com> wrote:
>>>>
>>>>
>>>>
>>>> On 10/14/20 8:07 AM, Ethan Zhao wrote:
>>>>> On Wed, Oct 14, 2020 at 5:00 PM Kuppuswamy Sathyanarayanan
>>>>> <sathyanarayanan.nkuppuswamy@gmail.com> wrote:
>>>>>>
>>>>>> Commit bdb5ac85777d ("PCI/ERR: Handle fatal error recovery")
>>>>>> merged fatal and non-fatal error recovery paths, and also made
>>>>>> recovery code depend on hotplug handler for "remove affected
>>>>>> device + rescan" support. But this change also complicated the
>>>>>> error recovery path and which in turn led to the following
>>>>>> issues.
>>>>>>
>>>>>> 1. We depend on hotplug handler for removing the affected
>>>>>> devices/drivers on DLLSC LINK down event (on DPC event
>>>>>> trigger) and DPC handler for handling the error recovery. Since
>>>>>> both handlers operate on same set of affected devices, it leads
>>>>>> to race condition, which in turn leads to NULL pointer
>>>>>> exceptions or error recovery failures.You can find more details
>>>>>> about this issue in following link.
>>>>>>
>>>>>> https://lore.kernel.org/linux-pci/20201007113158.48933-1-haifeng.zhao@intel.com/T/#t
>>>>>>
>>>>>> 2. For non-hotplug capable devices fatal (DPC) error recovery
>>>>>> is currently broken. Current fatal error recovery implementation
>>>>>> relies on PCIe hotplug (pciehp) handler for detaching and
>>>>>> re-enumerating the affected devices/drivers. So when dealing with
>>>>>> non-hotplug capable devices, recovery code does not restore the state
>>>>>> of the affected devices correctly. You can find more details about
>>>>>> this issue in the following links.
>>>>>>
>>>>>> https://lore.kernel.org/linux-pci/20200527083130.4137-1-Zhiqiang.Hou@nxp.com/
>>>>>> https://lore.kernel.org/linux-pci/12115.1588207324@famine/
>>>>>> https://lore.kernel.org/linux-pci/0e6f89cd6b9e4a72293cc90fafe93487d7c2d295.1585000084.git.sathyanarayanan.kuppuswamy@linux.intel.com/
>>>>>>
>>>>>> In order to fix the above two issues, we should stop relying on hotplug
>>>>> Yes, it doesn't rely on hotplug handler to remove and rescan the device,
>>>>> but it couldn't prevent hotplug drivers from doing another replicated
>>>>> removal/rescanning.
>>>>> it doesn't make sense to leave another useless removal/rescanning there.
>>>>> Maybe that's why these two paths were merged to one and made it rely on
>>>>> hotplug.
>>>> No, as per PCIe spec, hotplug and DPC has no functional dependency. Hence
>>>> depending on it to handle some of its recovery function is in-correct and
>>>> would lead to issues in non-hotplug capable platforms (which is true
>>>> currently).
>>>>>
>>

>
>>> Though pciehp is not so hot/scalable and performance critical, but there
>>> is per cpu thread to handle hot-plug operation. synchronize all threads
>>> make them walk backwards for scalability.
>> DPC events does not happen in high frequency. So I don't think we should
> It's holding global lock, once malfunction happens to one device and
> it's driver,
> the whole system, everyone holds it, would be blocked to work.
>> worry about the performance here. Even hotplug handler will hold this lock
>> when adding/removing the devices. So adding/removing devices is a serialized
> You don't worry about performance, but if there is a requirement needs
> more scalable
> and reliable hotplug, the effect will be much harder. what to do then ? choose
> another OS ?
As I have mentioned, all device creation/removal in PCI core code is already
protected by this lock (including hotplug code). So the multidomain performance
impact you mentioned should exist even now. All I am doing is, using the
same lock for protecting device removal/rescan in error recovery code.

drivers/pci/xen-pcifront.c:477: pci_lock_rescan_remove();
drivers/pci/xen-pcifront.c:567: pci_lock_rescan_remove();
drivers/pci/xen-pcifront.c:1064: pci_lock_rescan_remove();
drivers/pci/hotplug/rpaphp_core.c:498: pci_lock_rescan_remove();
drivers/pci/hotplug/rpaphp_core.c:520: pci_lock_rescan_remove();
drivers/pci/hotplug/s390_pci_hpc.c:70: pci_lock_rescan_remove();
drivers/pci/hotplug/shpchp_pci.c:31: pci_lock_rescan_remove();
drivers/pci/hotplug/shpchp_pci.c:73: pci_lock_rescan_remove();
drivers/pci/hotplug/pciehp_pci.c:39: pci_lock_rescan_remove();
drivers/pci/hotplug/pciehp_pci.c:96: pci_lock_rescan_remove();
drivers/pci/hotplug/acpiphp_glue.c:762: pci_lock_rescan_remove();
drivers/pci/hotplug/acpiphp_glue.c:787: pci_lock_rescan_remove();
drivers/pci/hotplug/acpiphp_glue.c:975: pci_lock_rescan_remove();
drivers/pci/hotplug/acpiphp_glue.c:1026: pci_lock_rescan_remove();
drivers/pci/hotplug/cpqphp_pci.c:75: pci_lock_rescan_remove();
drivers/pci/hotplug/cpqphp_pci.c:120: pci_lock_rescan_remove();
drivers/pci/hotplug/rpadlpar_core.c:361: pci_lock_rescan_remove();
drivers/pci/hotplug/pnv_php.c:513: pci_lock_rescan_remove();
drivers/pci/hotplug/pnv_php.c:582: pci_lock_rescan_remove();
drivers/pci/hotplug/ibmphp_core.c:668: pci_lock_rescan_remove();
drivers/pci/hotplug/ibmphp_core.c:738: pci_lock_rescan_remove();
drivers/pci/hotplug/cpci_hotplug_pci.c:245: pci_lock_rescan_remove();
drivers/pci/hotplug/cpci_hotplug_pci.c:298: pci_lock_rescan_remove();
drivers/pci/controller/pci-hyperv.c:1866: pci_lock_rescan_remove();
drivers/pci/controller/pci-hyperv.c:2135: pci_lock_rescan_remove();
drivers/pci/controller/pci-hyperv.c:2313: pci_lock_rescan_remove();
drivers/pci/controller/pci-hyperv.c:3300: pci_lock_rescan_remove();
drivers/pci/controller/pci-host-common.c:91: pci_lock_rescan_remove();
drivers/pci/remove.c:123: pci_lock_rescan_remove();
drivers/pci/pci-sysfs.c:410: pci_lock_rescan_remove();
drivers/pci/pci-sysfs.c:444: pci_lock_rescan_remove();
drivers/pci/pci-sysfs.c:479: pci_lock_rescan_remove();
drivers/pci/probe.c:3231:void pci_lock_rescan_remove(void)
drivers/pci/probe.c:3235:EXPORT_SYMBOL_GPL(pci_lock_rescan_remove);

> To be honest, I don't like the global lock/ pci_lock_rescan_remove().
>
> BTW, I didn't try the FATAL errors brute force injection on your
> patch, duplicated
> removal will work naturally because it was removed ?
>
> Thanks,
> Ethan
>> operation.
>>>
>>
>>>>
>>>>>> --
>>>>>> 2.17.1
>>>>>>
>>>>
>>>> --
>>>> Sathyanarayanan Kuppuswamy
>>>> Linux Kernel Developer
>>
>> --
>> Sathyanarayanan Kuppuswamy
>> Linux Kernel Developer

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer