Patch "PCI/ASPM: Handle PCI-to-PCIe bridges as roots of PCIe hierarchies" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
pci-aspm-handle-pci-to-pcie-bridges-as-roots-of-pcie-hierarchies.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Bjorn Helgaas <[email protected]>
Date: Fri, 27 Jan 2017 15:00:45 -0600
Subject: PCI/ASPM: Handle PCI-to-PCIe bridges as roots of PCIe hierarchies

From: Bjorn Helgaas <[email protected]>

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.

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

@@ -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;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/pci-aspm-handle-pci-to-pcie-bridges-as-roots-of-pcie-hierarchies.patch