diff --git a/src/kernel/async_task.rs b/src/kernel/async_task.rs
index f372143c15e6a8a82d5cf630f3a3baa9f16c7ccb..cdc698cd2d92e65f22f4b6efab98c09496b379e1 100644
--- a/src/kernel/async_task.rs
+++ b/src/kernel/async_task.rs
@@ -154,9 +154,9 @@ impl<T: TaskOwner> FairQueue<T> {
                     self.len -= 1;
                     res
                 }
-                None => panic!(""),
+                None => None,
             },
-            None => panic!("front: queue empty"),
+            None => None,
         }
     }
 
@@ -164,9 +164,9 @@ impl<T: TaskOwner> FairQueue<T> {
         match self.queue.front() {
             Some(owner) => match self.map.get(owner) {
                 Some(sub_queue) => sub_queue.front(),
-                None => panic!(""),
+                None => None,
             },
-            None => panic!("front: queue empty"),
+            None => None,
         }
     }
 
@@ -174,7 +174,7 @@ impl<T: TaskOwner> FairQueue<T> {
         match self.map.remove(&owner) {
             Some(sub_queue) => {
                 self.len -= sub_queue.len();
-                self.queue = self.queue.drain_filter(|x| *x == owner).collect();
+                self.queue.drain_filter(|x| *x == owner);
             }
             None => {}
         }
@@ -517,11 +517,6 @@ pub fn remove_async_used_info(vm_id: usize) {
 pub fn remove_vm_async_task(vm_id: usize) {
     let mut io_list = ASYNC_IO_TASK_LIST.lock();
     let mut ipi_list = ASYNC_IPI_TASK_LIST.lock();
-    // io_list.retain(|x| x.src_vmid != vm_id);
-    // ipi_list.retain(|x| x.src_vmid != vm_id);
-    // *io_list = io_list.drain_filter(|x| x.src_vmid == vm_id).collect::<LinkedList<_>>();
     io_list.remove(vm_id);
-    *ipi_list = ipi_list
-        .drain_filter(|x| x.src_vmid == vm_id)
-        .collect::<LinkedList<_>>();
+    ipi_list.drain_filter(|x| x.src_vmid == vm_id);
 }