diff --git a/kernel/comps/softirq/src/taskless.rs b/kernel/comps/softirq/src/taskless.rs
index 36e4b1608..03a35e80f 100644
--- a/kernel/comps/softirq/src/taskless.rs
+++ b/kernel/comps/softirq/src/taskless.rs
@@ -8,7 +8,7 @@ use core::{
 };
 
 use intrusive_collections::{intrusive_adapter, LinkedList, LinkedListAtomicLink};
-use ostd::{cpu::local::StaticCpuLocal, cpu_local, trap};
+use ostd::{cpu::local::StaticCpuLocal, cpu_local, sync::SpinLock, trap};
 
 use super::{
     softirq_id::{TASKLESS_SOFTIRQ_ID, TASKLESS_URGENT_SOFTIRQ_ID},
@@ -58,7 +58,7 @@ pub struct Taskless {
     /// Whether the taskless job is running.
     is_running: AtomicBool,
     /// The function that will be called when executing this taskless job.
-    callback: Box<RefCell<dyn FnMut() + Send + Sync + 'static>>,
+    callback: Box<SpinLock<dyn FnMut() + Send + Sync + 'static>>,
     /// Whether this `Taskless` is disabled.
     is_disabled: AtomicBool,
     link: LinkedListAtomicLink,
@@ -77,14 +77,10 @@ impl Taskless {
     where
         F: FnMut() + Send + Sync + 'static,
     {
-        // Since the same taskless will not be executed concurrently,
-        // it is safe to use a `RefCell` here though the `Taskless` will
-        // be put into an `Arc`.
-        #[expect(clippy::arc_with_non_send_sync)]
         Arc::new(Self {
             is_scheduled: AtomicBool::new(false),
             is_running: AtomicBool::new(false),
-            callback: Box::new(RefCell::new(callback)),
+            callback: Box::new(SpinLock::new(callback)),
             is_disabled: AtomicBool::new(false),
             link: LinkedListAtomicLink::new(),
         })
@@ -185,9 +181,7 @@ fn taskless_softirq_handler(
 
         taskless.is_scheduled.store(false, Ordering::Release);
 
-        // The same taskless will not be executing concurrently, so it is safe to
-        // do `borrow_mut` here.
-        (taskless.callback.borrow_mut())();
+        (taskless.callback.lock())();
         taskless.is_running.store(false, Ordering::Release);
     }
 }
diff --git a/ostd/src/cpu/local/mod.rs b/ostd/src/cpu/local/mod.rs
index 260848fcf..1a57007fd 100644
--- a/ostd/src/cpu/local/mod.rs
+++ b/ostd/src/cpu/local/mod.rs
@@ -162,12 +162,14 @@ impl<'a, T: 'static, S: AnyStorage<T>> Deref for CpuLocalDerefGuard<'a, T, S> {
     }
 }
 
-// SAFETY: At any given time, only one task can access the inner value `T` of a
-// CPU-local variable if `T` is not `Sync`. We guarantee it by disabling the
-// reference to the inner value, or turning off preemptions when creating
-// the reference.
-unsafe impl<T: 'static, S: AnyStorage<T>> Sync for CpuLocal<T, S> {}
-unsafe impl<T: 'static> Send for CpuLocal<T, DynamicStorage<T>> {}
+// SAFETY: Although multiple tasks may access the inner value `T` of a CPU-local
+// variable at different times, only one task can access it at any given moment.
+// We guarantee it by disabling the reference to the inner value, or turning off
+// preemptions when creating the reference. Therefore, if `T` is `Send`, marking
+// `CpuLocal<T, S>` with `Sync` and `Send` only safely transfer ownership of the
+// entire `T` instance between tasks.
+unsafe impl<T: Send + 'static, S: AnyStorage<T>> Sync for CpuLocal<T, S> {}
+unsafe impl<T: Send + 'static> Send for CpuLocal<T, DynamicStorage<T>> {}
 
 // Implement `!Copy` and `!Clone` for `CpuLocal` to ensure memory safety:
 // - Prevent valid instances of `CpuLocal<T, StaticStorage<T>>` from being copied
diff --git a/ostd/src/mm/heap/slot_list.rs b/ostd/src/mm/heap/slot_list.rs
index 22818af14..7aaf98972 100644
--- a/ostd/src/mm/heap/slot_list.rs
+++ b/ostd/src/mm/heap/slot_list.rs
@@ -16,6 +16,13 @@ pub struct SlabSlotList<const SLOT_SIZE: usize> {
     head: Option<NonNull<u8>>,
 }
 
+// SAFETY: Any access or modification (i.e., push and pop operations) to the
+// data pointed to by `head` requires a `&mut SlabSlotList`. Therefore, at any
+// given time, only one task can access the inner `head`. Additionally, a
+// `HeapSlot` will not be allocated again as long as it remains in the list.
+unsafe impl<const SLOT_SIZE: usize> Sync for SlabSlotList<SLOT_SIZE> {}
+unsafe impl<const SLOT_SIZE: usize> Send for SlabSlotList<SLOT_SIZE> {}
+
 impl<const SLOT_SIZE: usize> Default for SlabSlotList<SLOT_SIZE> {
     fn default() -> Self {
         Self::new()