[PATCH 4.4 01/29] PCI/ASPM: Handle PCI-to-PCIe bridges as roots of PCIe hierarchies

Greg Kroah-Hartman
2017-02-07T12:46:15Z

From: Bjorn Helgaas <bhelgaas@google.com>

commit 030305d69fc6963c16003f50d7e8d74b02d0a143 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/pci/pcie/aspm.c | 19 +++++++++++++------
1 file changed, 13 insertions(+), 6 deletions(-)

--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -518,25 +518,32 @@ static struct pcie_link_state *alloc_pci
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;