diff --git a/os/src/console.rs b/os/src/console.rs
index f95963c6..31614c64 100644
--- a/os/src/console.rs
+++ b/os/src/console.rs
@@ -1,6 +1,5 @@
 use crate::drivers::chardev::{CharDevice, UART};
 use core::fmt::{self, Write};
-use crate::sbi::console_putchar;
 
 struct Stdout;
 
@@ -8,7 +7,6 @@ impl Write for Stdout {
     fn write_str(&mut self, s: &str) -> fmt::Result {
         for c in s.chars() {
             UART.write(c as u8);
-            //console_putchar(c as usize);
         }
         Ok(())
     }
diff --git a/os/src/drivers/block/virtio_blk.rs b/os/src/drivers/block/virtio_blk.rs
index 26967f7b..a30e3bf8 100644
--- a/os/src/drivers/block/virtio_blk.rs
+++ b/os/src/drivers/block/virtio_blk.rs
@@ -28,17 +28,10 @@ impl BlockDevice for VirtIOBlock {
         let nb = *DEV_NON_BLOCKING_ACCESS.exclusive_access();
         if nb {
             let mut resp = BlkResp::default();
-            /*
             let task_cx_ptr = self.virtio_blk.exclusive_session(|blk| {
                 let token = unsafe { blk.read_block_nb(block_id, buf, &mut resp).unwrap() };
                 self.condvars.get(&token).unwrap().wait_no_sched()
             });
-            */
-            let mut blk = self.virtio_blk.exclusive_access();
-            let token = unsafe { blk.read_block_nb(block_id, buf, &mut resp).unwrap() };
-            //println!("waiting on token {}", token);
-            let task_cx_ptr = self.condvars.get(&token).unwrap().wait_no_sched();
-            drop(blk);
             schedule(task_cx_ptr);
             assert_eq!(
                 resp.status(),
@@ -56,16 +49,10 @@ impl BlockDevice for VirtIOBlock {
         let nb = *DEV_NON_BLOCKING_ACCESS.exclusive_access();
         if nb {
             let mut resp = BlkResp::default();
-            /*
             let task_cx_ptr = self.virtio_blk.exclusive_session(|blk| {
                 let token = unsafe { blk.write_block_nb(block_id, buf, &mut resp).unwrap() };
                 self.condvars.get(&token).unwrap().wait_no_sched()
             });
-            */
-            let mut blk = self.virtio_blk.exclusive_access();
-            let token = unsafe { blk.write_block_nb(block_id, buf, &mut resp).unwrap() };
-            let task_cx_ptr = self.condvars.get(&token).unwrap().wait_no_sched();
-            drop(blk);
             schedule(task_cx_ptr);
             assert_eq!(
                 resp.status(),
@@ -80,21 +67,11 @@ impl BlockDevice for VirtIOBlock {
         }
     }
     fn handle_irq(&self) {
-        //println!("into handle_irq");
-        /*
         self.virtio_blk.exclusive_session(|blk| {
-            //println!("not panic here");
             while let Ok(token) = blk.pop_used() {
-                //println!("wakeup virtio.token {}", token);
                 self.condvars.get(&token).unwrap().signal();
             }
         });
-        */
-        let mut blk = self.virtio_blk.exclusive_access();
-        while let Ok(token) = blk.pop_used() {
-            //println!("wakeup virtio.token {}", token);
-            self.condvars.get(&token).unwrap().signal();
-        }
     }
 }
 
diff --git a/os/src/drivers/chardev/ns16550a.rs b/os/src/drivers/chardev/ns16550a.rs
index 40c1b47c..667a6604 100644
--- a/os/src/drivers/chardev/ns16550a.rs
+++ b/os/src/drivers/chardev/ns16550a.rs
@@ -146,7 +146,6 @@ impl<const BASE_ADDR: usize> NS16550a<BASE_ADDR> {
 
 impl<const BASE_ADDR: usize> CharDevice for NS16550a<BASE_ADDR> {
     fn read(&self) -> u8 {
-        //println!("NS16550a::read");
         loop {
             let mut inner = self.inner.exclusive_access();
             if let Some(ch) = inner.read_buffer.pop_front() {
@@ -154,7 +153,6 @@ impl<const BASE_ADDR: usize> CharDevice for NS16550a<BASE_ADDR> {
             } else {
                 let task_cx_ptr = self.condvar.wait_no_sched();
                 drop(inner);
-                //println!("before scheduling");
                 schedule(task_cx_ptr);
             }
         }
@@ -164,15 +162,13 @@ impl<const BASE_ADDR: usize> CharDevice for NS16550a<BASE_ADDR> {
         inner.ns16550a.write(ch);
     }
     fn handle_irq(&self) {
-        let mut inner = self.inner.exclusive_access();
         let mut count = 0;
-        while let Some(ch) = inner.ns16550a.read() {
-            //println!("got {}", ch as char);
-            count += 1;
-            inner.read_buffer.push_back(ch);
-        }
-        drop(inner);
-        //assert_eq!(count, 1);
+        self.inner.exclusive_session(|inner| {
+            while let Some(ch) = inner.ns16550a.read() {
+                count += 1;
+                inner.read_buffer.push_back(ch);
+            }
+        });
         if count > 0 {
             self.condvar.signal();
         }
diff --git a/os/src/drivers/plic.rs b/os/src/drivers/plic.rs
index b1f662f3..77bad5f3 100644
--- a/os/src/drivers/plic.rs
+++ b/os/src/drivers/plic.rs
@@ -62,6 +62,7 @@ impl PLIC {
             self.priority_ptr(intr_source_id).write_volatile(priority);
         }
     }
+    #[allow(unused)]
     pub fn get_priority(&mut self, intr_source_id: usize) -> u32 {
         unsafe { self.priority_ptr(intr_source_id).read_volatile() & 7 }
     }
@@ -100,6 +101,7 @@ impl PLIC {
             threshold_ptr.write_volatile(threshold);
         }
     }
+    #[allow(unused)]
     pub fn get_threshold(&mut self, hart_id: usize, target_priority: IntrTargetPriority) -> u32 {
         let threshold_ptr = self.threshold_ptr_of_hart_with_priority(hart_id, target_priority);
         unsafe { threshold_ptr.read_volatile() & 7 }
diff --git a/os/src/sync/condvar.rs b/os/src/sync/condvar.rs
index b23d22e7..c50a53e2 100644
--- a/os/src/sync/condvar.rs
+++ b/os/src/sync/condvar.rs
@@ -28,30 +28,27 @@ impl Condvar {
         }
     }
 
+    /*
     pub fn wait(&self) {
         let mut inner = self.inner.exclusive_access();
         inner.wait_queue.push_back(current_task().unwrap());
         drop(inner);
         block_current_and_run_next();
     }
+    */
 
     pub fn wait_no_sched(&self) -> *mut TaskContext {
-        /*
         self.inner.exclusive_session(|inner| {
             inner.wait_queue.push_back(current_task().unwrap());
         });
-        */
-        let mut inner = self.inner.exclusive_access();
-        inner.wait_queue.push_back(current_task().unwrap());
-        drop(inner);
         block_current_task()
     }
 
     pub fn wait_with_mutex(&self, mutex: Arc<dyn Mutex>) {
         mutex.unlock();
-        let mut inner = self.inner.exclusive_access();
-        inner.wait_queue.push_back(current_task().unwrap());
-        drop(inner);
+        self.inner.exclusive_session(|inner| {
+            inner.wait_queue.push_back(current_task().unwrap());
+        });
         block_current_and_run_next();
         mutex.lock();
     }
diff --git a/os/src/sync/up.rs b/os/src/sync/up.rs
index f8579ead..55c8d40a 100644
--- a/os/src/sync/up.rs
+++ b/os/src/sync/up.rs
@@ -107,12 +107,10 @@ impl<T> UPIntrFreeCell<T> {
         UPIntrRefMut(Some(self.inner.borrow_mut()))
     }
 
-    /*
     pub fn exclusive_session<F, V>(&self, f: F) -> V where F: FnOnce(&mut T) -> V {
         let mut inner = self.exclusive_access();
         f(inner.deref_mut())
     }
-    */
 }
 
 impl<'a, T> Drop for UPIntrRefMut<'a, T> {
diff --git a/os/src/task/processor.rs b/os/src/task/processor.rs
index 347d3725..f196f681 100644
--- a/os/src/task/processor.rs
+++ b/os/src/task/processor.rs
@@ -39,11 +39,10 @@ pub fn run_tasks() {
         if let Some(task) = fetch_task() {
             let idle_task_cx_ptr = processor.get_idle_task_cx_ptr();
             // access coming task TCB exclusively
-            let mut task_inner = task.inner_exclusive_access();
-            let next_task_cx_ptr = &task_inner.task_cx as *const TaskContext;
-            task_inner.task_status = TaskStatus::Running;
-            drop(task_inner);
-            // release coming task TCB manually
+            let next_task_cx_ptr = task.inner.exclusive_session(|task_inner| {
+                task_inner.task_status = TaskStatus::Running;
+                &task_inner.task_cx as *const TaskContext
+            });
             processor.current = Some(task);
             // release processor manually
             drop(processor);
@@ -95,9 +94,9 @@ pub fn current_kstack_top() -> usize {
 }
 
 pub fn schedule(switched_task_cx_ptr: *mut TaskContext) {
-    let mut processor = PROCESSOR.exclusive_access();
-    let idle_task_cx_ptr = processor.get_idle_task_cx_ptr();
-    drop(processor);
+    let idle_task_cx_ptr = PROCESSOR.exclusive_session(|processor| {
+        processor.get_idle_task_cx_ptr()
+    });
     unsafe {
         __switch(switched_task_cx_ptr, idle_task_cx_ptr);
     }
diff --git a/os/src/task/task.rs b/os/src/task/task.rs
index 7b65ee6b..85d949f8 100644
--- a/os/src/task/task.rs
+++ b/os/src/task/task.rs
@@ -9,7 +9,7 @@ pub struct TaskControlBlock {
     pub process: Weak<ProcessControlBlock>,
     pub kstack: KernelStack,
     // mutable
-    inner: UPIntrFreeCell<TaskControlBlockInner>,
+    pub inner: UPIntrFreeCell<TaskControlBlockInner>,
 }
 
 impl TaskControlBlock {