Hello,
> When BIOS neglects to assign bus numbers to PCI bridges, the kernel
> attempts to correct that during PCI device enumeration. If it runs out
> of bus numbers, no pci_bus is allocated and the "subordinate" pointer in
> the bridge's pci_dev remains NULL.
>
> The PCIe bandwidth controller erroneously does not check for a NULL
> subordinate pointer and dereferences it on probe.
>
> Bandwidth control of unusable devices below the bridge is of questionable
> utility, so simply error out instead. This mirrors what PCIe hotplug does
> since commit 62e4492c3063 ("PCI: Prevent NULL dereference during pciehp
> probe").
>
> The PCI core emits a message with KERN_INFO severity if it has run out of
> bus numbers. PCIe hotplug emits an additional message with KERN_ERR
> severity to inform the user that hotplug functionality is disabled at the
> bridge. A similar message for bandwidth control does not seem merited,
> given that its only purpose so far is to expose an up-to-date link speed
> in sysfs and throttle the link speed on certain laptops with limited
> Thermal Design Power. So error out silently.
>
> User-visible messages:
>
> pci 0000:16:02.0: bridge configuration invalid ([bus 00-00]), reconfiguring
> [...]
> pci_bus 0000:45: busn_res: [bus 45-74] end is updated to 74
> pci 0000:16:02.0: devices behind bridge are unusable because [bus 45-74] cannot be assigned for them
> [...]
> pcieport 0000:16:02.0: pciehp: Hotplug bridge without secondary bus, ignoring
> [...]
> BUG: kernel NULL pointer dereference
> RIP: pcie_update_link_speed
> pcie_bwnotif_enable
> pcie_bwnotif_probe
> pcie_port_probe_service
> really_probe
Applied to bwctrl, thank you!
Krzysztof
