Messages in this thread | | | Subject | Re: [PATCH v1 1/1] PCI/ERR: Handle fatal error recovery for non-hotplug capable devices | From | "Kuppuswamy, Sathyanarayanan" <> | Date | Thu, 14 May 2020 13:36:09 -0700 |
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Hi Bjorn,
On 5/13/20 3:44 PM, Bjorn Helgaas wrote: > On Wed, May 06, 2020 at 08:32:59PM -0700, sathyanarayanan.kuppuswamy@linux.intel.com wrote: >> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> >> >> 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. > > Apparently this fixes a bug. Can you include a link to a problem > report? The above is a description of a *solution*, but it's hard to > understand without starting with the problem itself.
Let me add the problem description to the commit log in next version.
Adding it here for discussion.
Current pcie_do_recovery() implementation has following three issues:
1. Fatal (DPC) error recovery is currently broken for non-hotplug capable devices. Current DPC recovery implementation relies on hotplug handler for detaching/re-enumerating the affected devices/drivers on DLLSC state changes. So when dealing with non-hotplug capable devices, recovery code does not restore the state of the affected devices correctly. Correct implementation should call report_mmio_enabled() and report_slot_reset() functions after reseting the link/device which is currently missing.
2. For non-fatal errors if report_error_detected() or report_mmio_enabled() functions requests PCI_ERS_RESULT_NEED_RESET then current pcie_do_recovery() implementation does not do the requested explicit device reset, instead just calls the report_slot_reset() on all affected devices. Notifying about the reset via report_slot_reset() without doing the actual device reset is incorrect.
3. For fatal errors, pcie_do_recovery() function currently completely ignores the status result of report_error_detected() call. After calling reset_link() function then status value gets updated to either PCI_ERS_RESULT_DISCONNECT or PCI_ERS_RESULT_RECOVERED, and the initial value returned from report_error_detected() is totally ignored. For solving the issue # 1, we need to update the status only if reset_link() call failed and returns PCI_ERS_RESULT_DISCONNECT. Otherwise recovery handler should proceed to call report_mmio_enabled() and report_slot_reset().
> > The above talks about reset_link(), which is only used in the > io_frozen case. In that case, I think the only thing this patch > changes is that when reset_link() fails, we'll return with > PCI_ERS_RESULT_DISCONNECT instead of whatever reset_link() > returned. Yes, if reset_link() is successful then we let pcie_do_recovery() proceed to call report_slot_reset() with initial status value returned from report_error_detected() function call. > > What this patch *does* change is that in the normal_detected case, we > previously never called reset_link() but now we will if an > .error_detected() callback requested it. yes, as highlighted in issue # 1 this patch adds support to call reset_link() if report_error_detected() function requests it. > >> 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. > > Sorry, I'm not following this explanation. IIUC this fixes a bug when > the channel is frozen and .error_detected() returns NEED_RESET. > > In that case, the current code does: > > * state == io_frozen > * .error_detected() returns status == NEED_RESET > * status = reset_link() > * if status != RECOVERED, we return status > * otherwise status == RECOVERED > * we do not call report_slot_reset() > * we return RECOVERED > > It does seem like we *should* call the .slot_reset() callbacks, but > the only time we return recovery failure is if reset_link() failed. > > I can certainly understand if drivers don't recover when we reset > their device but don't call their .slot_reset() callback. Is that > what this fixes? > > After the patch, > > * state == io_frozen > * .error_detected() returns status == NEED_RESET > * we set status = NEED_RESET (doesn't change anything in this case) > * we call reset_link() > * if reset_link() failed, we return DISCONNECT > * otherwise continue with status == NEED_RESET > * we *do* call report_slot_reset() > * we return whatever .slot_reset() returned > > I think the change to call .slot_reset() makes sense, but that's not > at all clear from the commit log. Am I understanding the behavior > correctly? Yes, your understanding is correct. I hope above mentioned error description clarifies it. > >> 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. > > Use "pcie_do_recovery()" and "report_slot_reset()" (including the > parentheses) to follow convention. Also fix other occurrences above. will fix it in next version. > >> [original patch is from jay.vosburgh@canonical.com] >> [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@canonical.com> >> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> >> --- >> 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) >> + status = PCI_ERS_RESULT_DISCONNECT; >> + } else { >> + if (pci_bus_error_reset(dev)) >> + status = PCI_ERS_RESULT_DISCONNECT; > > As far as I can tell, there is no caller of pcie_do_recovery() where > reset_link is NULL, so this call of pci_bus_error_reset() looks like > dead code. Yes, I will remove the if (reset_link) check. > > We did not previously check whether reset_link was NULL, and this > patch changes nothing that could result in it being NULL. > >> + } >> + >> + 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) { >> -- >> 2.17.1 >>
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