dm mpath: use hw_handler_params if attached hw_handler is same as requested

Let the requested m->hw_handler_params be used if the attached hardware
handler is the same handler as requested with m->hw_handler_name.
Signed-off-by: tang.junhui <tang.junhui@zte.com.cn>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-mpath.c

@@ -849,19 +849,23 @@ static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps
 retain:
 		attached_handler_name = scsi_dh_attached_handler_name(q, GFP_KERNEL);
 		if (attached_handler_name) {
+			/*
+			 * Clear any hw_handler_params associated with a
+			 * handler that isn't already attached.
+			 */
+			if (m->hw_handler_name && strcmp(attached_handler_name, m->hw_handler_name)) {
+				kfree(m->hw_handler_params);
+				m->hw_handler_params = NULL;
+			}
+
 			/*
 			 * Reset hw_handler_name to match the attached handler
-			 * and clear any hw_handler_params associated with the
-			 * ignored handler.
 			 *
 			 * NB. This modifies the table line to show the actual
 			 * handler instead of the original table passed in.
 			 */
 			kfree(m->hw_handler_name);
 			m->hw_handler_name = attached_handler_name;
-
-			kfree(m->hw_handler_params);
-			m->hw_handler_params = NULL;
 		}
 	}