On Thu, Nov 15, 2012 at 12:09 AM, Pandarathil, Vijaymohan R <vijaymohan.pandarathil@xxxxxx> wrote: > Thanks for the comments. See my response below. > >> -----Original Message----- >> From: Bjorn Helgaas [mailto:bhelgaas@xxxxxxxxxx] >> Sent: Wednesday, November 14, 2012 4:51 PM >> To: Pandarathil, Vijaymohan R >> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx; >> linasvepstas@xxxxxxxxx; Myron Stowe; Ortiz, Lance E; Huang Ying; Hidetoshi >> Seto; Patterson, Andrew D (LeftHand Networks); Zhang Yanmin >> Subject: Re: [ PATCH RESEND ] PCI-AER: Do not report successful error >> recovery for devices with AER-unaware drivers >> >> [+cc Lance, Huang, Hidetoshi, Andrew, Zhang] >> >> On Sat, Nov 10, 2012 at 07:41:04AM +0000, Pandarathil, Vijaymohan R wrote: >> > When an error is detected on a PCIe device which does not have an >> > AER-aware driver, prevent AER infrastructure from reporting >> > successful error recovery. >> > >> > This is because the report_error_detected() function that gets >> > called in the first phase of recovery process allows forward >> > progress even when the driver for the device does not have AER >> > capabilities. It seems that all callbacks (in pci_error_handlers >> > structure) registered by drivers that gets called during error >> > recovery are not mandatory. So the intention of the infrastructure >> > design seems to be to allow forward progress even when a specific >> > callback has not been registered by a driver. However, if error >> > handler structure itself has not been registered, it doesn't make >> > sense to allow forward progress. >> > >> > As a result of the current design, in the case of a single device >> > having an AER-unaware driver or in the case of any function in a >> > multi-function card having an AER-unaware driver, a successful >> > recovery is reported. >> > >> > Typical scenario this happens is when a PCI device is detached >> > from a KVM host and the pci-stub driver on the host claims the >> > device. The pci-stub driver does not have error handling capabilities >> > but the AER infrastructure still reports that the device recovered >> > successfully. >> > >> > The changes proposed here leaves the device in an unrecovered state >> > if the driver for the device or for any function in a multi-function >> > card does not have error handler structure registered. This reflects >> > the true state of the device and prevents any partial recovery (or no >> > recovery at all) reported as successful. >> > >> > Please also see comments from Linas Vepstas at the following link >> > http://www.spinics.net/lists/linux-pci/msg18572.html >> > >> > Reviewed-by: Linas Vepstas <linasvepstas <at> gmail.com> >> > Reviewed-by: Myron Stowe <mstowe <at> redhat.com> >> > Signed-off-by: Vijay Mohan Pandarathil <vijaymohan.pandarathil <at> >> hp.com> >> > >> > --- >> > >> > drivers/pci/pcie/aer/aerdrv_core.c | 6 ++++++ >> > 1 file changed, 6 insertions(+) >> > >> > diff --git a/drivers/pci/pcie/aer/aerdrv_core.c >> b/drivers/pci/pcie/aer/aerdrv_core.c >> > index 06bad96..030b229 100644 >> > --- a/drivers/pci/pcie/aer/aerdrv_core.c >> > +++ b/drivers/pci/pcie/aer/aerdrv_core.c >> > @@ -215,6 +215,12 @@ static int report_error_detected(struct pci_dev >> *dev, void *data) >> > >> > dev->error_state = result_data->state; >> > >> > + if ((!dev->driver || !dev->driver->err_handler) && >> > + !(dev->hdr_type & PCI_HEADER_TYPE_BRIDGE)) { >> > + dev_info(&dev->dev, "AER: Error detected but no driver has >> claimed this device or the driver is AER-unaware\n"); >> > + result_data->result = PCI_ERS_RESULT_NONE; >> > + return 1; >> >> This doesn't seem right because returning 1 here causes pci_walk_bus() >> to terminate, which means we won't set dev->error_state or notify >> drivers for any devices we haven't visited yet. >> >> > + } >> > if (!dev->driver || >> > !dev->driver->err_handler || >> > !dev->driver->err_handler->error_detected) { >> >> If none of the drivers in the affected hierarchy supports error handling, >> I think the call tree looks like this: >> >> do_recovery # uncorrectable only >> broadcast_error_message(dev, ..., report_error_detected) >> result_data.result = CAN_RECOVER >> pci_walk_bus(..., report_error_detected) >> report_error_detected # (each dev in subtree) >> return 0 # no change to result >> return result_data.result >> broadcast_error_message(dev, ..., report_mmio_enabled) >> result_data.result = PCI_ERS_RESULT_RECOVERED >> pci_walk_bus(..., report_mmio_enabled) >> report_mmio_enabled # (each dev in subtree) >> return 0 # no change to result >> dev_info("recovery successful") >> >> Specifically, there are no error_handler functions, so we never change >> result_data.result, and the default is that we treat the error as >> "recovered successfully." That seems broken. An uncorrectable error >> is by definition recoverable only by device-specific software, i.e., >> the driver. We didn't call any drivers, so we can't have recovered >> anything. >> >> What do you think of the following alternative? I don't know why you >> checked for bridge devices in your patch, so I don't know whether >> that's important here or not. >> >> diff --git a/drivers/pci/pcie/aer/aerdrv_core.c >> b/drivers/pci/pcie/aer/aerdrv_core.c >> index 06bad96..a109c68 100644 >> --- a/drivers/pci/pcie/aer/aerdrv_core.c >> +++ b/drivers/pci/pcie/aer/aerdrv_core.c >> @@ -231,11 +231,11 @@ static int report_error_detected(struct pci_dev *dev, >> void *data) >> dev->driver ? >> "no AER-aware driver" : "no driver"); >> } >> - return 0; >> + vote = PCI_ERS_RESULT_DISCONNECT; >> + } else { >> + err_handler = dev->driver->err_handler; >> + vote = err_handler->error_detected(dev, result_data->state); >> } >> - >> - err_handler = dev->driver->err_handler; >> - vote = err_handler->error_detected(dev, result_data->state); >> result_data->result = merge_result(result_data->result, vote); >> return 0; >> } > > This would definitely set the error_state for all devices correctly. However, with the > current implementation of merge_result(), won't we still end up reporting successful > recovery ? The following case statement in merge_result() can set back the result > from PCI_ERS_RESULT_DISCONNECT to PCI_ERS_RESULT_NEED_RESET for a subsequent device > on the bus which returned PCI_ERS_RESULT_NEED_RESET from its error_detected callback . > > merge_result() > ... > case PCI_ERS_RESULT_DISCONNECT: > if (new == PCI_ERS_RESULT_NEED_RESET) > orig = new; > break; > > This would mean do_recovery() proceeds along to the next broadcast_message and > ultimately report success. Right ? Let me know if I am missing something. Yes, I think you're right. I only looked at the case where none of the devices in the subtree had drivers. > I looked at a few options and the following looked more promising. Thoughts ? > > Introduce a new pci_ers_result enum PCI_ERS_RESULT_NO_AER_DRIVER and make changes as follows. I don't really like this new enum because it's not really obvious how it's different from PCI_ERS_RESULT_NONE and, more importantly, it makes merge_result() even more of a kludge than it already is. It's hard to write a nice simple description of this algorithm (visiting all the devices in a subtree, collecting error handler results, and merging them). It would be a lot easier to describe if merge_result() could be written simply as "max()", but I'm not sure the pci_ers_result codes could be ordered in a way that would make that possible. And the desired semantics might make it impossible, too. I think the intent of your patch is that if there's any device in the subtree that lacks an .error_detected() method, we do not call .mmio_enabled() or .slot_reset() or .resume() for *any* device in the subtree. Right? So maybe this is the best we can do, and it certainly seems better than what we have now. Can you repost this as a fresh v2 patch? > diff --git a/drivers/pci/pcie/aer/aerdrv.h b/drivers/pci/pcie/aer/aerdrv.h > index 94a7598..149ba79 100644 > --- a/drivers/pci/pcie/aer/aerdrv.h > +++ b/drivers/pci/pcie/aer/aerdrv.h > @@ -87,6 +87,9 @@ struct aer_broadcast_data { > static inline pci_ers_result_t merge_result(enum pci_ers_result orig, > enum pci_ers_result new) > { > + if (new == PCI_ERS_RESULT_NO_AER_DRIVER) > + return new; BTW, if you keep this, please just use "return PCI_ERS_RESULT_NO_AER_DRIVER" rather than "return new" since we *know* what we're returning. I think there's another instance of this in merge_result() that you could fix, too. > + > if (new == PCI_ERS_RESULT_NONE) > return orig; > > diff --git a/drivers/pci/pcie/aer/aerdrv_core.c b/drivers/pci/pcie/aer/aerdrv_core.c > index 06bad96..729580a 100644 > --- a/drivers/pci/pcie/aer/aerdrv_core.c > +++ b/drivers/pci/pcie/aer/aerdrv_core.c > @@ -231,11 +231,12 @@ static int report_error_detected(struct pci_dev *dev, void *data) > dev->driver ? > "no AER-aware driver" : "no driver"); > } > - return 0; > + vote = PCI_ERS_RESULT_NO_AER_DRIVER; > + } else { > + err_handler = dev->driver->err_handler; > + vote = err_handler->error_detected(dev, result_data->state); > } > > - err_handler = dev->driver->err_handler; > - vote = err_handler->error_detected(dev, result_data->state); > result_data->result = merge_result(result_data->result, vote); > return 0; > } > diff --git a/include/linux/pci.h b/include/linux/pci.h > index ee21795..fb7e869 100644 > --- a/include/linux/pci.h > +++ b/include/linux/pci.h > @@ -538,6 +538,9 @@ enum pci_ers_result { > > /* Device driver is fully recovered and operational */ > PCI_ERS_RESULT_RECOVERED = (__force pci_ers_result_t) 5, > + > + /* No AER capabilities registered for the driver */ > + PCI_ERS_RESULT_NO_AER_DRIVER = (__force pci_ers_result_t) 6, > }; > > /* PCI bus error event callbacks */ > -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
