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+

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 17ac1dce32867051298a5489841de8b636835a68..3dd8bcbb3011babd4ad4271d6f6f64733bd9b3f1 100644 (file)
--- 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;