Messages in this thread | | | Subject | Re: [PATCH v6 2/2] PCI/ERR: Split the fatal and non-fatal error recovery handling | From | "Kuppuswamy, Sathyanarayanan" <> | Date | Wed, 14 Oct 2020 22:53:36 -0700 |
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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
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