diff --git a/kernel/src/arch/riscv32/compiler_rt.rs b/kernel/src/arch/riscv32/compiler_rt.rs
index 80dbdf8..aaf9be0 100644
--- a/kernel/src/arch/riscv32/compiler_rt.rs
+++ b/kernel/src/arch/riscv32/compiler_rt.rs
@@ -69,4 +69,27 @@ pub unsafe extern fn __atomic_compare_exchange_1(dst: *mut u8, expected: *mut u8
 #[no_mangle]
 pub unsafe extern fn __atomic_compare_exchange_4(dst: *mut u32, expected: *mut u32, desired: u32) -> bool {
     __atomic_compare_exchange(dst, expected, desired)
+}
+
+
+#[no_mangle]
+pub unsafe extern fn __atomic_fetch_add_4(dst: *mut u32, delta: u32) -> u32 {
+    use super::interrupt;
+    let flags = interrupt::disable_and_store();
+    let val = read(dst);
+    let new_val = val + delta;
+    write(dst, new_val);
+    interrupt::restore(flags);
+    val
+}
+
+#[no_mangle]
+pub unsafe extern fn __atomic_fetch_sub_4(dst: *mut u32, delta: u32) -> u32 {
+    use super::interrupt;
+    let flags = interrupt::disable_and_store();
+    let val = read(dst);
+    let new_val = val - delta;
+    write(dst, new_val);
+    interrupt::restore(flags);
+    val
 }
\ No newline at end of file
diff --git a/kernel/src/lib.rs b/kernel/src/lib.rs
index 28ef150..685eeea 100644
--- a/kernel/src/lib.rs
+++ b/kernel/src/lib.rs
@@ -69,8 +69,8 @@ pub fn kmain() -> ! {
     // the test is not supported in riscv32(maybe)
     //thread::test::local_key();
     //thread::test::unpack();
-    //sync::test::philosopher_using_mutex();
-    //sync::test::philosopher_using_monitor();
+    sync::test::philosopher_using_mutex();
+    sync::test::philosopher_using_monitor();
     //sync::mpsc::test::test_all();
 
     // come into shell
diff --git a/kernel/src/sync/mutex.rs b/kernel/src/sync/mutex.rs
index c8e62ea..73e902b 100644
--- a/kernel/src/sync/mutex.rs
+++ b/kernel/src/sync/mutex.rs
@@ -96,11 +96,17 @@ impl<T, S: MutexSupport> Mutex<T, S>
 impl<T: ?Sized, S: MutexSupport> Mutex<T, S>
 {
     fn obtain_lock(&self) {
-        while self.lock.compare_and_swap(false, true, Ordering::Acquire) != false {
-            // Wait until the lock looks unlocked before retrying
-            while self.lock.load(Ordering::Relaxed) {
-                self.support.cpu_relax();
-            }
+        while true {
+            match self.lock.compare_exchange(false, true, Ordering::Acquire, Ordering::Acquire) {
+                Ok(X) => break,
+                Err(X) => {
+                    // Wait until the lock looks unlocked before retrying
+                    while self.lock.load(Ordering::Relaxed) {
+                        self.support.cpu_relax();
+                    }
+                },
+            };
+            
         }
     }
 
@@ -144,13 +150,13 @@ impl<T: ?Sized, S: MutexSupport> Mutex<T, S>
     /// a guard within Some.
     pub fn try_lock(&self) -> Option<MutexGuard<T, S>> {
         let support_guard = S::before_lock();
-        if self.lock.compare_and_swap(false, true, Ordering::Acquire) == false {
-            Some(MutexGuard {
-                mutex: self,
-                support_guard,
-            })
-        } else {
-            None
+        match self.lock.compare_exchange(false, true, Ordering::Acquire, Ordering::Acquire) {
+            Ok(X)   =>
+                Some(MutexGuard {
+                    mutex: self,
+                    support_guard,
+                }), 
+            Err(X)  => None,
         }
     }
 }