diff --git a/os/src/batch.rs b/os/src/batch.rs
index f2a0d649..816e8b78 100644
--- a/os/src/batch.rs
+++ b/os/src/batch.rs
@@ -116,6 +116,8 @@ pub fn run_next_app() -> ! {
     }
     app_manager.move_to_next_app();
     drop(app_manager);
+    // before this we have to drop local variables related to resources manually
+    // and release the resources
     extern "C" { fn __restore(cx_addr: usize); }
     unsafe {
         __restore(KERNEL_STACK.push_context(