[PATCH] Fix 3bc95598 'powerpc/PCI: Use list_for_each_entry() for bus traversal'

[Mike Qiu <qiudayu@linux.vnet.ibm.com>]

Unable to handle kernel paging request for data at address 0x00000000
Faulting instruction address: 0xc000000000041d78
Oops: Kernel access of bad area, sig: 11 [#1]
...
NIP [c000000000041d78] .sys_pciconfig_iobase+0x68/0x1f0
LR [c000000000041e0c] .sys_pciconfig_iobase+0xfc/0x1f0
Call Trace:
[c0000003b4787db0] [c000000000041e0c] .sys_pciconfig_iobase+0xfc/0x1f0 (unreliable)
[c0000003b4787e30] [c000000000009ed8] syscall_exit+0x0/0x98

This bug was introduced by commit 3bc955987fb377f3c95bc29deb498e96819b8451
The root cause was the 'bus' has been set to null while try to access
bus->next.

Signed-off-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/pci_64.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/pci_64.c b/arch/powerpc/kernel/pci_64.c
index 2a47790..7b6c1ae 100644
--- a/arch/powerpc/kernel/pci_64.c
+++ b/arch/powerpc/kernel/pci_64.c
@@ -209,6 +209,7 @@ long sys_pciconfig_iobase(long which, unsigned long in_bus,
 {
 	struct pci_controller* hose;
 	struct pci_bus *bus = NULL;
+	struct pci_bus *tmp_bus = NULL;
 	struct device_node *hose_node;
 
 	/* Argh ! Please forgive me for that hack, but that's the
@@ -229,10 +230,12 @@ long sys_pciconfig_iobase(long which, unsigned long in_bus,
 	 * used on pre-domains setup. We return the first match
 	 */
 
-	list_for_each_entry(bus, &pci_root_buses, node) {
-		if (in_bus >= bus->number && in_bus <= bus->busn_res.end)
+	list_for_each_entry(tmp_bus, &pci_root_buses, node) {
+		if (in_bus >= tmp_bus->number &&
+		    in_bus <= tmp_bus->busn_res.end) {
+			bus = tmp_bus;
 			break;
-		bus = NULL;
+		}
 	}
 	if (bus == NULL || bus->dev.of_node == NULL)
 		return -ENODEV;
-- 
1.8.0.1