IB/ipath: Add locking for interrupt use of ipath_pd contexts vs free

Fixes timing race resulting in panic.  Not a performance sensitive path.

Signed-off-by: Dave Olson <dave.olson@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/ipath/ipath_verbs.c

@@ -1852,7 +1852,7 @@ unsigned ipath_get_npkeys(struct ipath_devdata *dd)
 }
 
 /**
- * ipath_get_pkey - return the indexed PKEY from the port 0 PKEY table
+ * ipath_get_pkey - return the indexed PKEY from the port PKEY table
  * @dd: the infinipath device
  * @index: the PKEY index
  */
@@ -1860,6 +1860,7 @@ unsigned ipath_get_pkey(struct ipath_devdata *dd, unsigned index)
 {
 	unsigned ret;
 
+	/* always a kernel port, no locking needed */
 	if (index >= ARRAY_SIZE(dd->ipath_pd[0]->port_pkeys))
 		ret = 0;
 	else