PCI / ACPI: Do not set ACPI companions for host bridges with parents

Commit 97badf873ab6 (device property: Make it possible to use
secondary firmware nodes) uncovered a bug in the x86 (and ia64) PCI
host bridge initialization code that assumes bridge->bus->sysdata
to always point to a struct pci_sysdata object which need not be
the case (in particular, the Xen PCI frontend driver sets it to point
to a different data type).  If it is not the case, an incorrect
pointer (or a piece of data that is not a pointer at all) will be
passed to ACPI_COMPANION_SET() and that may cause interesting
breakage to happen going forward.

To work around this problem use the observation that the ACPI
host bridge initialization always passes NULL as parent to
pci_create_root_bus(), so if pcibios_root_bridge_prepare() sees
a non-NULL parent of the bridge, it should not attempt to set
an ACPI companion for it, because that means that
pci_create_root_bus() has been called by someone else.

Fixes: 97badf873ab6 (device property: Make it possible to use secondary firmware nodes)
Reported-and-tested-by: Sander Eikelenboom <linux@eikelenboom.it>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>

diff --git a/arch/ia64/pci/pci.c b/arch/ia64/pci/pci.c
index d4e162d35b3467b9d7814769129237583f8cb100..7cc3be9fa7c65a0dd700dfd30c04cc7be822922d 100644 (file)
--- a/arch/ia64/pci/pci.c
+++ b/arch/ia64/pci/pci.c
@@ -478,9 +478,16 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
 
 int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
 {
-       struct pci_controller *controller = bridge->bus->sysdata;
-
-       ACPI_COMPANION_SET(&bridge->dev, controller->companion);
+       /*
+        * We pass NULL as parent to pci_create_root_bus(), so if it is not NULL
+        * here, pci_create_root_bus() has been called by someone else and
+        * sysdata is likely to be different from what we expect.  Let it go in
+        * that case.
+        */
+       if (!bridge->dev.parent) {
+               struct pci_controller *controller = bridge->bus->sysdata;
+               ACPI_COMPANION_SET(&bridge->dev, controller->companion);
+       }
        return 0;
 }
 

diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
index d93963340c3c0d958385ce4ec8aadcdfe225a174..14a63ed6fe092cd3f512d155046942a28c3744e8 100644 (file)
--- a/arch/x86/pci/acpi.c
+++ b/arch/x86/pci/acpi.c
@@ -482,9 +482,16 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
 
 int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
 {
-       struct pci_sysdata *sd = bridge->bus->sysdata;
-
-       ACPI_COMPANION_SET(&bridge->dev, sd->companion);
+       /*
+        * We pass NULL as parent to pci_create_root_bus(), so if it is not NULL
+        * here, pci_create_root_bus() has been called by someone else and
+        * sysdata is likely to be different from what we expect.  Let it go in
+        * that case.
+        */
+       if (!bridge->dev.parent) {
+               struct pci_sysdata *sd = bridge->bus->sysdata;
+               ACPI_COMPANION_SET(&bridge->dev, sd->companion);
+       }
        return 0;
 }