powerpc/eeh: Null check uses of eeh_pe_bus_get

eeh_pe_bus_get() can return NULL if a PCI bus isn't found for a given PE.
Some callers don't check this, and can cause a null pointer dereference
under certain circumstances.

Fix this by checking NULL everywhere eeh_pe_bus_get() is called.

Fixes: 8a6b1bc70dbb ("powerpc/eeh: EEH core to handle special event")
Cc: stable@vger.kernel.org # v3.11+
Signed-off-by: Russell Currey <ruscur@russell.cc>
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/eeh_driver.c

@@ -994,6 +994,14 @@ static void eeh_handle_special_event(void)
 				/* Notify all devices to be down */
 				eeh_pe_state_clear(pe, EEH_PE_PRI_BUS);
 				bus = eeh_pe_bus_get(phb_pe);
+				if (!bus) {
+					pr_err("%s: Cannot find PCI bus for "
+					       "PHB#%d-PE#%x\n",
+					       __func__,
+					       pe->phb->global_number,
+					       pe->addr);
+					break;
+				}
 				eeh_pe_dev_traverse(pe,
 					eeh_report_failure, NULL);
 				pci_hp_remove_devices(bus);

arch/powerpc/platforms/powernv/eeh-powernv.c

@@ -1091,6 +1091,11 @@ static int pnv_eeh_reset(struct eeh_pe *pe, int option)
 	}
 
 	bus = eeh_pe_bus_get(pe);
+	if (!bus) {
+		pr_err("%s: Cannot find PCI bus for PHB#%d-PE#%x\n",
+			__func__, pe->phb->global_number, pe->addr);
+		return -EIO;
+	}
 	if (pe->type & EEH_PE_VF)
 		return pnv_eeh_reset_vf_pe(pe, option);