PCI/ASPM: Handle PCI-to-PCIe bridges as roots of PCIe hierarchies

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: 51ebfc92b72b ("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+

1 files changed, 13 insertions, 6 deletions

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 17ac1dce3286..3dd8bcbb3011 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -532,25 +532,32 @@ static struct pcie_link_state *alloc_pcie_link_state(struct pci_dev *pdev)
         link = kzalloc(sizeof(*link), GFP_KERNEL);
         if (!link)
                 return NULL;
+
         INIT_LIST_HEAD(&link->sibling);
         INIT_LIST_HEAD(&link->children);
         INIT_LIST_HEAD(&link->link);
         link->pdev = pdev;
-        if (pci_pcie_type(pdev) != PCI_EXP_TYPE_ROOT_PORT) {
+
+        /*
+         * Root Ports and PCI/PCI-X to PCIe Bridges are roots of PCIe
+         * hierarchies.
+         */
+        if (pci_pcie_type(pdev) == PCI_EXP_TYPE_ROOT_PORT ||
+            pci_pcie_type(pdev) == PCI_EXP_TYPE_PCIE_BRIDGE) {
+                link->root = link;
+        } else {
                 struct pcie_link_state *parent;
+
                 parent = pdev->bus->parent->self->link_state;
                 if (!parent) {
                         kfree(link);
                         return NULL;
                 }
+
                 link->parent = parent;
+                link->root = link->parent->root;
                 list_add(&link->link, &parent->children);
         }
-        /* Setup a pointer to the root port link */
-        if (!link->parent)
-                link->root = link;
-        else
-                link->root = link->parent->root;
 
         list_add(&link->sibling, &link_list);
         pdev->link_state = link;