On 09/14/2012 12:43 AM, Bjorn Helgaas wrote: > I didn't intend this change in behavior, so in that sense, this is a > regression. We could restore the previous behavior by changing > pci_stop_and_remove_bus_device() so the "pci_remove_bus(); > dev->subordinate = NULL;" code is after the pci_stop_dev() call, as > you suggest. > > But I'm not 100% sure that's the correct fix. I think it's possible > to have a bridge device that has no secondary bus. For example, I > don't think a bridge configured with "secondary > subordinate", e.g., > "[bus ff-00]", will forward any config transactions downstream. In > that case, we'll have a struct pci_dev for the bridge device, but > there won't be a struct pci_bus for the secondary bus, so > dev->subordinate will be NULL. There are actually quite a few > existing tests for this situation in pnv_ioda_setup_bus_PE(), > eeh_add_device_tree_late(), yenta_probe(), etc. > > When we enumerate bridges, we build the bridge pci_dev before building > the downstream pci_bus, so symmetry suggests that we should tear down > the pci_bus before tearing down the pci_dev. > > So I wonder if a better fix is remove the assumption that > "dev->subordinate != NULL means this is a bridge device." There are > many places where we test "dev->subordinate" to iterate through > downstream devices or something similar; those should be fine. We'd > only have to change the places that care about actual type of the > device, e.g., the config space differences between header types. > > Where did you trip over this? If you just found this by inspection, > my congratulations, it's a pretty subtle issue :) HI Bjorn, This issue was disclosed when developing the patch set "[PATCH v2 0/9] enhance PCI related drivers to handle hotplug events". BTW, I have sent this patch set to you just now. We are not assume that dev->subordinate is not NULL for a bridge device, but that dev->subordinate is consistent when PCI bus notification callbacks are called for BUS_NOTIFY_ADD_DEVICE and BUS_NOTIFY_DEL_DEVICE. Thanks! Gerry -- 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
