Re: [PATCH v1 1/1] PCI/ERR: Handle fatal error recovery for non-hotplug capable devices

[Kuppuswamy, Sathyanarayanan]

On 5/21/20 3:58 AM, Yicong Yang wrote:
> On 2020/5/21 1:04, Kuppuswamy, Sathyanarayanan wrote:
> > On 5/20/20 1:28 AM, Yicong Yang wrote:
> > > On 2020/5/7 11:32, sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx wrote:
> > > > From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> > > >
> > > > If there are non-hotplug capable devices connected to a given
> > > > port, then during the fatal error recovery(triggered by DPC or
> > > > AER), after calling reset_link() function, we cannot rely on
> > > > hotplug handler to detach and re-enumerate the device drivers
> > > > in the affected bus. Instead, we will have to let the error
> > > > recovery handler call report_slot_reset() for all devices in
> > > > the bus to notify about the reset operation. Although this is
> > > > only required for non hot-plug capable devices, doing it for
> > > > hotplug capable devices should not affect the functionality.
> > > >
> > > > Along with above issue, this fix also applicable to following
> > > > issue.
> > > >
> > > > Commit 6d2c89441571 ("PCI/ERR: Update error status after
> > > > reset_link()") added support to store status of reset_link()
> > > > call. Although this fixed the error recovery issue observed if
> > > > the initial value of error status is PCI_ERS_RESULT_DISCONNECT
> > > > or PCI_ERS_RESULT_NO_AER_DRIVER, it also discarded the status
> > > > result from report_frozen_detected. This can cause a failure to
> > > > recover if _NEED_RESET is returned by report_frozen_detected and
> > > > report_slot_reset is not invoked.
> > > >
> > > > Such an event can be induced for testing purposes by reducing the
> > > > Max_Payload_Size of a PCIe bridge to less than that of a device
> > > > downstream from the bridge, and then initiating I/O through the
> > > > device, resulting in oversize transactions.  In the presence of DPC,
> > > > this results in a containment event and attempted reset and recovery
> > > > via pcie_do_recovery.  After 6d2c89441571 report_slot_reset is not
> > > > invoked, and the device does not recover.
> > > >
> > > > [original patch is from jay.vosburgh@xxxxxxxxxxxxx]
> > > > [original patch link https://lore.kernel.org/linux-pci/18609.1588812972@famine/]
> > > > Fixes: 6d2c89441571 ("PCI/ERR: Update error status after reset_link()")
> > > > Signed-off-by: Jay Vosburgh <jay.vosburgh@xxxxxxxxxxxxx>
> > > > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> > > > ---
> > > >    drivers/pci/pcie/err.c | 19 +++++++++++++++----
> > > >    1 file changed, 15 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> > > > index 14bb8f54723e..db80e1ecb2dc 100644
> > > > --- a/drivers/pci/pcie/err.c
> > > > +++ b/drivers/pci/pcie/err.c
> > > > @@ -165,13 +165,24 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
> > > >        pci_dbg(dev, "broadcast error_detected message\n");
> > > >        if (state == pci_channel_io_frozen) {
> > > >            pci_walk_bus(bus, report_frozen_detected, &status);
> > > > -        status = reset_link(dev);
> > > > -        if (status != PCI_ERS_RESULT_RECOVERED) {
> > > > +        status = PCI_ERS_RESULT_NEED_RESET;
> > > > +    } else {
> > > > +        pci_walk_bus(bus, report_normal_detected, &status);
> > > > +    }
> > > > +
> > > > +    if (status == PCI_ERS_RESULT_NEED_RESET) {
> > > > +        if (reset_link) {
> > > > +            if (reset_link(dev) != PCI_ERS_RESULT_RECOVERED)
> > >
> > > we'll call reset_link() only if link is frozen. so it may have problem here.
> > you mean before this change right?
> > After this change, reset_link() will be called as long as status is
> > PCI_ERS_RESULT_NEED_RESET.
>
> Yes. I think we should reset the link only if the io is blocked as before. There's
> no reason to reset a normal link.
Currently, only AER and DPC driver uses pcie_do_recovery() call. So the
possible reset_link options are dpc_reset_link() and aer_root_reset().

In dpc_reset_link() case, the link is already disabled and hence we
don't need to do another reset. In case of aer_root_reset() it
uses pci_bus_error_reset() to reset the slot.
> Furthermore, PCI_ERS_RESULT_NEED_RESET means device driver requires a slot reset rather
> than a link reset, so it maybe improper to use it to judge whether a link reset is needed.
> We decide whether to do a link reset only by the io state.
>
> Thanks,
> Yicong
>
>
> > > Thanks,
> > > Yicong
> > >
> > >
> > > > +                status = PCI_ERS_RESULT_DISCONNECT;
> > > > +        } else {
> > > > +            if (pci_bus_error_reset(dev))
> > > > +                status = PCI_ERS_RESULT_DISCONNECT;
> > > > +        }
> > > > +
> > > > +        if (status == PCI_ERS_RESULT_DISCONNECT) {
> > > >                pci_warn(dev, "link reset failed\n");
> > > >                goto failed;
> > > >            }
> > > > -    } else {
> > > > -        pci_walk_bus(bus, report_normal_detected, &status);
> > > >        }
> > > >          if (status == PCI_ERS_RESULT_CAN_RECOVER) {
> > .