[PATCH] stop elv_unregister() from rogering other iosched's data, fix locking

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 18cf1f3..f65766e 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -48,6 +48,7 @@
 
 	elevator_init_fn *elevator_init_fn;
 	elevator_exit_fn *elevator_exit_fn;
+	void (*trim)(struct io_context *);
 };
 
 #define ELV_NAME_MAX	(16)