diff --git a/crate/memory/src/memory_set/mod.rs b/crate/memory/src/memory_set/mod.rs
index 12cd767f..f6324bb4 100644
--- a/crate/memory/src/memory_set/mod.rs
+++ b/crate/memory/src/memory_set/mod.rs
@@ -252,7 +252,7 @@ impl<T: PageTableExt> MemorySet<T> {
                     // subset
                     let area = self.areas.remove(i);
                     area.unmap(&mut self.page_table);
-                    i -= 1;
+                    i = i.wrapping_sub(1);
                 } else if self.areas[i].start_addr >= start_addr
                     && self.areas[i].start_addr < end_addr
                 {
@@ -324,7 +324,7 @@ impl<T: PageTableExt> MemorySet<T> {
                     i += 1;
                 }
             }
-            i += 1;
+            i = i.wrapping_add(1);
         }
     }
 
diff --git a/kernel/src/sync/condvar.rs b/kernel/src/sync/condvar.rs
index 75784669..03f99fc2 100644
--- a/kernel/src/sync/condvar.rs
+++ b/kernel/src/sync/condvar.rs
@@ -25,7 +25,9 @@ impl Condvar {
         Condvar::default()
     }
 
-    pub fn wait_queue_len(&self) -> usize { self.wait_queue.lock().len() }
+    pub fn wait_queue_len(&self) -> usize {
+        self.wait_queue.lock().len()
+    }
 
     /// Park current thread and wait for this condvar to be notified.
     #[deprecated(note = "this may leads to lost wakeup problem. please use `wait` instead.")]
diff --git a/kernel/src/sync/semaphore.rs b/kernel/src/sync/semaphore.rs
index c1c6edca..ab7aae82 100644
--- a/kernel/src/sync/semaphore.rs
+++ b/kernel/src/sync/semaphore.rs
@@ -7,7 +7,6 @@ use super::SpinNoIrqLock as Mutex;
 use crate::syscall::SysError;
 use core::cell::Cell;
 use core::ops::Deref;
-use crate::process::Pid;
 
 struct SemaphoreInner {
     pub count: isize,
@@ -95,8 +94,12 @@ impl Semaphore {
         self.cvar.wait_queue_len()
     }
 
-    pub fn get_pid(&self) -> usize { self.lock.lock().pid }
-    pub fn set_pid(&self, pid: usize) { self.lock.lock().pid = pid; }
+    pub fn get_pid(&self) -> usize {
+        self.lock.lock().pid
+    }
+    pub fn set_pid(&self, pid: usize) {
+        self.lock.lock().pid = pid;
+    }
 
     /// Set the current count
     pub fn set(&self, value: isize) {
diff --git a/kernel/src/syscall/ipc.rs b/kernel/src/syscall/ipc.rs
index f1e86987..044fa0f6 100644
--- a/kernel/src/syscall/ipc.rs
+++ b/kernel/src/syscall/ipc.rs
@@ -74,7 +74,8 @@ impl Syscall<'_> {
                 Ok(0)
             }
             IPC_STAT => {
-                *unsafe { self.vm().check_write_ptr(arg as *mut SemidDs)? } = *sem_array.semid_ds.lock();
+                *unsafe { self.vm().check_write_ptr(arg as *mut SemidDs)? } =
+                    *sem_array.semid_ds.lock();
                 Ok(0)
             }
             _ => {