In a struct pcie_link_state, link->root points to the pcie_link_state of
the root of the PCIe hierarchy. For the topmost link, this points to
itself (link->root = link). For others, we copy the pointer from the
parent (link->root = link->parent->root).
Previously we recognized that Root Ports originated PCIe hierarchies, but
we treated PCI/PCI-X to PCIe Bridges as being in the middle of the
hierarchy, and when we tried to copy the pointer from link->parent->root,
there was no parent, and we dereferenced a NULL pointer:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000090
IP: [<ffffffff9e424350>] pcie_aspm_init_link_state+0x170/0x820
Recognize that PCI/PCI-X to PCIe Bridges originate PCIe hierarchies just
like Root Ports do, so link->root for these devices should also point to
itself.
Fixes: 51ebfc92b7 ("PCI: Enumerate switches below PCI-to-PCIe bridges")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=193411
Link: https://bugzilla.opensuse.org/show_bug.cgi?id=1022181
Tested-by: lists@ssl-mail.com
Tested-by: Jayachandran C. <jnair@caviumnetworks.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: stable@vger.kernel.org # v4.2+
030305d69f