> -----Original Message----- > From: Bjorn Helgaas [mailto:bhelgaas@xxxxxxxxxx] > Sent: Thursday, November 15, 2012 5:09 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 > > 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? Right. BTW, I did look at usage of PCI_ERS_RESULT_NONE in all places. It seemed to me that the intended semantics of PCI_ERS_RESULT_NONE may not have been followed everywhere and I did not want to take a risk of breaking something else at this time. I will see if I can cleanup merge_result() as a separate patch in future. > > 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? Okay. I will post a 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. Will do. > > > + > > 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
