powerpc/eeh: Wrong place to call pci_get_slot()

pci_get_slot() is called with hold of PCI bus semaphore and it's not
safe to be called in interrupt context. However, we possibly checks
EEH error and calls the function in interrupt context. To avoid using
pci_get_slot(), we turn into device tree for fetching location code.
Otherwise, we might run into WARN_ON() as following messages indicate:

 WARNING: at drivers/pci/search.c:223
 CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.16.0-rc3+ #72
 task: c000000001367af0 ti: c000000001444000 task.ti: c000000001444000
 NIP: c000000000497b70 LR: c000000000037530 CTR: 000000003003d114
 REGS: c000000001446fa0 TRAP: 0700   Not tainted  (3.16.0-rc3+)
 MSR: 9000000000029032 <SF,HV,EE,ME,IR,DR,RI>  CR: 48002422  XER: 20000000
 CFAR: c00000000003752c SOFTE: 0
   :
 NIP [c000000000497b70] .pci_get_slot+0x40/0x110
 LR [c000000000037530] .eeh_pe_loc_get+0x150/0x190
 Call Trace:
   .of_get_property+0x30/0x60 (unreliable)
   .eeh_pe_loc_get+0x150/0x190
   .eeh_dev_check_failure+0x1b4/0x550
   .eeh_check_failure+0x90/0xf0
   .lpfc_sli_check_eratt+0x504/0x7c0 [lpfc]
   .lpfc_poll_eratt+0x64/0x100 [lpfc]
   .call_timer_fn+0x64/0x190
   .run_timer_softirq+0x2cc/0x3e0

Cc: stable@vger.kernel.org
Signed-off-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>
Acked-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/eeh_pe.c

@@ -791,53 +791,33 @@ void eeh_pe_restore_bars(struct eeh_pe *pe)
  */
 const char *eeh_pe_loc_get(struct eeh_pe *pe)
 {
-	struct pci_controller *hose;
 	struct pci_bus *bus = eeh_pe_bus_get(pe);
-	struct pci_dev *pdev;
-	struct device_node *dn;
-	const char *loc;
+	struct device_node *dn = pci_bus_to_OF_node(bus);
+	const char *loc = NULL;
 
-	if (!bus)
-		return "N/A";
+	if (!dn)
+		goto out;
 
 	/* PHB PE or root PE ? */
 	if (pci_is_root_bus(bus)) {
-		hose = pci_bus_to_host(bus);
-		loc = of_get_property(hose->dn,
-				"ibm,loc-code", NULL);
-		if (loc)
-			return loc;
-		loc = of_get_property(hose->dn,
-				"ibm,io-base-loc-code", NULL);
+		loc = of_get_property(dn, "ibm,loc-code", NULL);
+		if (!loc)
+			loc = of_get_property(dn, "ibm,io-base-loc-code", NULL);
 		if (loc)
-			return loc;
-
-		pdev = pci_get_slot(bus, 0x0);
-	} else {
-		pdev = bus->self;
-	}
-
-	if (!pdev) {
-		loc = "N/A";
 			goto out;
-	}
 
-	dn = pci_device_to_OF_node(pdev);
-	if (!dn) {
-		loc = "N/A";
+		/* Check the root port */
+		dn = dn->child;
+		if (!dn)
 			goto out;
 	}
 
 	loc = of_get_property(dn, "ibm,loc-code", NULL);
 	if (!loc)
 		loc = of_get_property(dn, "ibm,slot-location-code", NULL);
-	if (!loc)
-		loc = "N/A";
 
 out:
-	if (pci_is_root_bus(bus) && pdev)
-		pci_dev_put(pdev);
-	return loc;
+	return loc ? loc : "N/A";
 }
 
 /**