-You may need to add or modify code where interrupts are already
-disabled, such as in @func{sema_up} or @func{sema_down}. You should
-still try to keep this code as short as you can.
+The synchronization primitives themselves in @file{synch.c} are
+implemented by disabling interrupts. You may need to increase the
+amount of code that runs with interrupts disabled here, but you should
+still try to keep it to a minimum.