tokio: enable the unsafe_op_in_unsafe_fn lint at the crate level (#7711)

Signed-off-by: ADD-SP <[email protected]>

tokio/src/fs/file.rs

@@ -917,7 +917,9 @@ impl std::os::unix::io::AsFd for File {
 #[cfg(unix)]
 impl std::os::unix::io::FromRawFd for File {
     unsafe fn from_raw_fd(fd: std::os::unix::io::RawFd) -> Self {
-        StdFile::from_raw_fd(fd).into()
+        // Safety: exactly the same safety contract as
+        // `std::os::unix::io::FromRawFd::from_raw_fd`.
+        unsafe { StdFile::from_raw_fd(fd).into() }
     }
 }
 
@@ -942,7 +944,9 @@ cfg_windows! {
 
     impl FromRawHandle for File {
         unsafe fn from_raw_handle(handle: RawHandle) -> Self {
-            StdFile::from_raw_handle(handle).into()
+            // Safety: exactly the same safety contract as
+            // `FromRawHandle::from_raw_handle`.
+            unsafe { StdFile::from_raw_handle(handle).into() }
         }
     }
 }

tokio/src/io/poll_evented.rs

@@ -171,7 +171,7 @@ feature! {
             loop {
                 let evt = ready!(self.registration.poll_read_ready(cx))?;
 
-                let b = &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]);
+                let b = unsafe { &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]) };
 
                 // used only when the cfgs below apply
                 #[allow(unused_variables)]
@@ -213,7 +213,7 @@ feature! {
 
                         // Safety: We trust `TcpStream::read` to have filled up `n` bytes in the
                         // buffer.
-                        buf.assume_init(n);
+                        unsafe { buf.assume_init(n) };
                         buf.advance(n);
                         return Poll::Ready(Ok(()));
                     },

tokio/src/io/read_buf.rs

@@ -283,7 +283,9 @@ unsafe impl<'a> bytes::BufMut for ReadBuf<'a> {
 
     // SAFETY: The caller guarantees that at least `cnt` unfilled bytes have been initialized.
     unsafe fn advance_mut(&mut self, cnt: usize) {
-        self.assume_init(cnt);
+        unsafe {
+            self.assume_init(cnt);
+        }
         self.advance(cnt);
     }
 
@@ -311,16 +313,32 @@ impl fmt::Debug for ReadBuf<'_> {
     }
 }
 
+/// # Safety
+///
+/// The caller must ensure that `slice` is fully initialized
+/// and never writes uninitialized bytes to the returned slice.
 unsafe fn slice_to_uninit_mut(slice: &mut [u8]) -> &mut [MaybeUninit<u8>] {
-    &mut *(slice as *mut [u8] as *mut [MaybeUninit<u8>])
+    // SAFETY: `MaybeUninit<u8>` has the same memory layout as u8, and the caller
+    // promises to not write uninitialized bytes to the returned slice.
+    unsafe { &mut *(slice as *mut [u8] as *mut [MaybeUninit<u8>]) }
 }
 
+/// # Safety
+///
+/// The caller must ensure that `slice` is fully initialized.
 // TODO: This could use `MaybeUninit::slice_assume_init` when it is stable.
 unsafe fn slice_assume_init(slice: &[MaybeUninit<u8>]) -> &[u8] {
-    &*(slice as *const [MaybeUninit<u8>] as *const [u8])
+    // SAFETY: `MaybeUninit<u8>` has the same memory layout as u8, and the caller
+    // promises that `slice` is fully initialized.
+    unsafe { &*(slice as *const [MaybeUninit<u8>] as *const [u8]) }
 }
 
+/// # Safety
+///
+/// The caller must ensure that `slice` is fully initialized.
 // TODO: This could use `MaybeUninit::slice_assume_init_mut` when it is stable.
 unsafe fn slice_assume_init_mut(slice: &mut [MaybeUninit<u8>]) -> &mut [u8] {
-    &mut *(slice as *mut [MaybeUninit<u8>] as *mut [u8])
+    // SAFETY: `MaybeUninit<u8>` has the same memory layout as `u8`, and the caller
+    // promises that `slice` is fully initialized.
+    unsafe { &mut *(slice as *mut [MaybeUninit<u8>] as *mut [u8]) }
 }

tokio/src/lib.rs

@@ -10,7 +10,7 @@
     rust_2018_idioms,
     unreachable_pub
 )]
-#![deny(unused_must_use)]
+#![deny(unused_must_use, unsafe_op_in_unsafe_fn)]
 #![doc(test(
     no_crate_inject,
     attr(deny(warnings, rust_2018_idioms), allow(dead_code, unused_variables))

tokio/src/loom/std/atomic_u16.rs

@@ -26,7 +26,7 @@ impl AtomicU16 {
     /// All mutations must have happened before the unsynchronized load.
     /// Additionally, there must be no concurrent mutations.
     pub(crate) unsafe fn unsync_load(&self) -> u16 {
-        core::ptr::read(self.inner.get() as *const u16)
+        unsafe { core::ptr::read(self.inner.get() as *const u16) }
     }
 }
 

tokio/src/loom/std/atomic_u32.rs

@@ -26,7 +26,7 @@ impl AtomicU32 {
     /// All mutations must have happened before the unsynchronized load.
     /// Additionally, there must be no concurrent mutations.
     pub(crate) unsafe fn unsync_load(&self) -> u32 {
-        core::ptr::read(self.inner.get() as *const u32)
+        unsafe { core::ptr::read(self.inner.get() as *const u32) }
     }
 }
 

tokio/src/loom/std/atomic_usize.rs

@@ -26,7 +26,7 @@ impl AtomicUsize {
     /// All mutations must have happened before the unsynchronized load.
     /// Additionally, there must be no concurrent mutations.
     pub(crate) unsafe fn unsync_load(&self) -> usize {
-        core::ptr::read(self.inner.get() as *const usize)
+        unsafe { core::ptr::read(self.inner.get() as *const usize) }
     }
 
     pub(crate) fn with_mut<R>(&mut self, f: impl FnOnce(&mut usize) -> R) -> R {

tokio/src/macros/addr_of.rs

@@ -11,11 +11,16 @@ macro_rules! generate_addr_of_methods {
     )*}
     ) => {
         impl<$($gen)*> $struct_name {$(
+            #[doc = "# Safety"]
+            #[doc = ""]
+            #[doc = "The `me` pointer must be valid."]
             $(#[$attrs])*
             $vis unsafe fn $fn_name(me: ::core::ptr::NonNull<Self>) -> ::core::ptr::NonNull<$field_type> {
                 let me = me.as_ptr();
-                let field = ::std::ptr::addr_of_mut!((*me) $(.$field_name)+ );
-                ::core::ptr::NonNull::new_unchecked(field)
+                // safety: the caller guarantees that `me` is valid
+                let field = unsafe { ::std::ptr::addr_of_mut!((*me) $(.$field_name)+ ) };
+                // safety: the field pointer is never null
+                unsafe { ::core::ptr::NonNull::new_unchecked(field) }
             }
         )*}
     };

tokio/src/net/tcp/socket.rs

@@ -836,7 +836,9 @@ cfg_unix! {
         /// The caller is responsible for ensuring that the socket is in
         /// non-blocking mode.
         unsafe fn from_raw_fd(fd: RawFd) -> TcpSocket {
-            let inner = socket2::Socket::from_raw_fd(fd);
+            // Safety: exactly the same safety requirements as the
+            // `FromRawFd::from_raw_fd` trait method.
+            let inner = unsafe { socket2::Socket::from_raw_fd(fd) };
             TcpSocket { inner }
         }
     }
@@ -875,7 +877,7 @@ cfg_windows! {
         /// The caller is responsible for ensuring that the socket is in
         /// non-blocking mode.
         unsafe fn from_raw_socket(socket: RawSocket) -> TcpSocket {
-            let inner = socket2::Socket::from_raw_socket(socket);
+            let inner = unsafe { socket2::Socket::from_raw_socket(socket) };
             TcpSocket { inner }
         }
     }

tokio/src/net/unix/socket.rs

@@ -259,7 +259,9 @@ impl AsFd for UnixSocket {
 
 impl FromRawFd for UnixSocket {
     unsafe fn from_raw_fd(fd: RawFd) -> UnixSocket {
-        let inner = socket2::Socket::from_raw_fd(fd);
+        // Safety: exactly the same safety requirements as the
+        // `FromRawFd::from_raw_fd` trait method.
+        let inner = unsafe { socket2::Socket::from_raw_fd(fd) };
         UnixSocket { inner }
     }
 }

tokio/src/net/windows/named_pipe.rs

@@ -126,7 +126,7 @@ impl NamedPipeServer {
     /// [Tokio Runtime]: crate::runtime::Runtime
     /// [enabled I/O]: crate::runtime::Builder::enable_io
     pub unsafe fn from_raw_handle(handle: RawHandle) -> io::Result<Self> {
-        let named_pipe = mio_windows::NamedPipe::from_raw_handle(handle);
+        let named_pipe = unsafe { mio_windows::NamedPipe::from_raw_handle(handle) };
 
         Ok(Self {
             io: PollEvented::new(named_pipe)?,
@@ -999,7 +999,7 @@ impl NamedPipeClient {
     /// [Tokio Runtime]: crate::runtime::Runtime
     /// [enabled I/O]: crate::runtime::Builder::enable_io
     pub unsafe fn from_raw_handle(handle: RawHandle) -> io::Result<Self> {
-        let named_pipe = mio_windows::NamedPipe::from_raw_handle(handle);
+        let named_pipe = unsafe { mio_windows::NamedPipe::from_raw_handle(handle) };
 
         Ok(Self {
             io: PollEvented::new(named_pipe)?,
@@ -2344,22 +2344,24 @@ impl ServerOptions {
             mode
         };
 
-        let h = windows_sys::CreateNamedPipeW(
-            addr.as_ptr(),
-            open_mode,
-            pipe_mode,
-            self.max_instances,
-            self.out_buffer_size,
-            self.in_buffer_size,
-            self.default_timeout,
-            attrs as *mut _,
-        );
+        let h = unsafe {
+            windows_sys::CreateNamedPipeW(
+                addr.as_ptr(),
+                open_mode,
+                pipe_mode,
+                self.max_instances,
+                self.out_buffer_size,
+                self.in_buffer_size,
+                self.default_timeout,
+                attrs as *mut _,
+            )
+        };
 
         if h == windows_sys::INVALID_HANDLE_VALUE {
             return Err(io::Error::last_os_error());
         }
 
-        NamedPipeServer::from_raw_handle(h as _)
+        unsafe { NamedPipeServer::from_raw_handle(h as _) }
     }
 }
 
@@ -2550,15 +2552,17 @@ impl ClientOptions {
         // we have access to windows_sys it ultimately doesn't hurt to use
         // `CreateFile` explicitly since it allows the use of our already
         // well-structured wide `addr` to pass into CreateFileW.
-        let h = windows_sys::CreateFileW(
-            addr.as_ptr(),
-            desired_access,
-            0,
-            attrs as *mut _,
-            windows_sys::OPEN_EXISTING,
-            self.get_flags(),
-            null_mut(),
-        );
+        let h = unsafe {
+            windows_sys::CreateFileW(
+                addr.as_ptr(),
+                desired_access,
+                0,
+                attrs as *mut _,
+                windows_sys::OPEN_EXISTING,
+                self.get_flags(),
+                null_mut(),
+            )
+        };
 
         if h == windows_sys::INVALID_HANDLE_VALUE {
             return Err(io::Error::last_os_error());
@@ -2566,15 +2570,16 @@ impl ClientOptions {
 
         if matches!(self.pipe_mode, PipeMode::Message) {
             let mode = windows_sys::PIPE_READMODE_MESSAGE;
-            let result =
-                windows_sys::SetNamedPipeHandleState(h, &mode, ptr::null_mut(), ptr::null_mut());
+            let result = unsafe {
+                windows_sys::SetNamedPipeHandleState(h, &mode, ptr::null_mut(), ptr::null_mut())
+            };
 
             if result == 0 {
                 return Err(io::Error::last_os_error());
             }
         }
 
-        NamedPipeClient::from_raw_handle(h as _)
+        unsafe { NamedPipeClient::from_raw_handle(h as _) }
     }
 
     fn get_flags(&self) -> u32 {
@@ -2659,13 +2664,15 @@ unsafe fn named_pipe_info(handle: RawHandle) -> io::Result<PipeInfo> {
     let mut in_buffer_size = 0;
     let mut max_instances = 0;
 
-    let result = windows_sys::GetNamedPipeInfo(
-        handle as _,
-        &mut flags,
-        &mut out_buffer_size,
-        &mut in_buffer_size,
-        &mut max_instances,
-    );
+    let result = unsafe {
+        windows_sys::GetNamedPipeInfo(
+            handle as _,
+            &mut flags,
+            &mut out_buffer_size,
+            &mut in_buffer_size,
+            &mut max_instances,
+        )
+    };
 
     if result == 0 {
         return Err(io::Error::last_os_error());

tokio/src/process/mod.rs

@@ -750,7 +750,7 @@ impl Command {
     where
         F: FnMut() -> io::Result<()> + Send + Sync + 'static,
     {
-        self.std.pre_exec(f);
+        unsafe { self.std.pre_exec(f) };
         self
     }
 

tokio/src/process/windows.rs

@@ -162,7 +162,7 @@ impl Drop for Waiting {
 }
 
 unsafe extern "system" fn callback(ptr: *mut std::ffi::c_void, _timer_fired: bool) {
-    let complete = &mut *(ptr as *mut Option<oneshot::Sender<()>>);
+    let complete = unsafe { &mut *(ptr as *mut Option<oneshot::Sender<()>>) };
     let _ = complete.take().unwrap().send(());
 }
 

tokio/src/runtime/handle.rs

@@ -392,6 +392,10 @@ impl Handle {
 
     #[track_caller]
     #[allow(dead_code)]
+    /// # Safety
+    ///
+    /// This must only be called in `LocalRuntime` if the runtime has been verified to be owned
+    /// by the current thread.
     pub(crate) unsafe fn spawn_local_named<F>(
         &self,
         future: F,
@@ -412,7 +416,7 @@ impl Handle {
         let future = super::task::trace::Trace::root(future);
         #[cfg(all(tokio_unstable, feature = "tracing"))]
         let future = crate::util::trace::task(future, "task", meta, id.as_u64());
-        self.inner.spawn_local(future, id, meta.spawned_at)
+        unsafe { self.inner.spawn_local(future, id, meta.spawned_at) }
     }
 
     /// Returns the flavor of the current `Runtime`.

tokio/src/runtime/io/registration_set.rs

@@ -119,7 +119,8 @@ impl RegistrationSet {
         let io = unsafe { NonNull::new_unchecked(Arc::as_ptr(io).cast_mut()) };
 
         super::EXPOSE_IO.unexpose_provenance(io.as_ptr());
-        let _ = synced.registrations.remove(io);
+        // SAFETY: the caller guarantees that `io` is part of this list.
+        let _ = unsafe { synced.registrations.remove(io) };
     }
 }
 
@@ -141,6 +142,8 @@ unsafe impl linked_list::Link for Arc<ScheduledIo> {
     unsafe fn pointers(
         target: NonNull<Self::Target>,
     ) -> NonNull<linked_list::Pointers<ScheduledIo>> {
-        NonNull::new_unchecked(target.as_ref().linked_list_pointers.get())
+        // safety: `target.as_ref().linked_list_pointers` is a `UnsafeCell` that
+        // always returns a non-null pointer.
+        unsafe { NonNull::new_unchecked(target.as_ref().linked_list_pointers.get()) }
     }
 }

tokio/src/runtime/io/scheduled_io.rs

@@ -417,7 +417,7 @@ unsafe impl linked_list::Link for Waiter {
     }
 
     unsafe fn pointers(target: NonNull<Waiter>) -> NonNull<linked_list::Pointers<Waiter>> {
-        Waiter::addr_of_pointers(target)
+        unsafe { Waiter::addr_of_pointers(target) }
     }
 }
 

tokio/src/runtime/park.rs

@@ -305,11 +305,15 @@ impl Inner {
         Arc::into_raw(this) as *const ()
     }
 
+    /// # Safety
+    ///
+    /// The pointer must have been created by [`Self::into_raw`].
     unsafe fn from_raw(ptr: *const ()) -> Arc<Inner> {
-        Arc::from_raw(ptr as *const Inner)
+        unsafe { Arc::from_raw(ptr as *const Inner) }
     }
 }
 
+// TODO: Is this really a unsafe function?
 unsafe fn unparker_to_raw_waker(unparker: Arc<Inner>) -> RawWaker {
     RawWaker::new(
         Inner::into_raw(unparker),
@@ -317,23 +321,39 @@ unsafe fn unparker_to_raw_waker(unparker: Arc<Inner>) -> RawWaker {
     )
 }
 
+/// # Safety
+///
+/// The pointer must have been created by [`Inner::into_raw`].
 unsafe fn clone(raw: *const ()) -> RawWaker {
-    Arc::increment_strong_count(raw as *const Inner);
-    unparker_to_raw_waker(Inner::from_raw(raw))
+    unsafe {
+        Arc::increment_strong_count(raw as *const Inner);
+    }
+    unsafe { unparker_to_raw_waker(Inner::from_raw(raw)) }
 }
 
+/// # Safety
+///
+/// The pointer must have been created by [`Inner::into_raw`].
 unsafe fn drop_waker(raw: *const ()) {
-    drop(Inner::from_raw(raw));
+    drop(unsafe { Inner::from_raw(raw) });
 }
 
+/// # Safety
+///
+/// The pointer must have been created by [`Inner::into_raw`].
 unsafe fn wake(raw: *const ()) {
-    let unparker = Inner::from_raw(raw);
+    let unparker = unsafe { Inner::from_raw(raw) };
     unparker.unpark();
 }
 
+/// # Safety
+///
+/// The pointer must have been created by [`Inner::into_raw`].
 unsafe fn wake_by_ref(raw: *const ()) {
     let raw = raw as *const Inner;
-    (*raw).unpark();
+    unsafe {
+        (*raw).unpark();
+    }
 }
 
 #[cfg(loom)]

tokio/src/runtime/scheduler/current_thread/mod.rs

@@ -474,6 +474,7 @@ impl Handle {
     /// Spawn a task which isn't safe to send across thread boundaries onto the runtime.
     ///
     /// # Safety
+    ///
     /// This should only be used when this is a `LocalRuntime` or in another case where the runtime
     /// provably cannot be driven from or moved to different threads from the one on which the task
     /// is spawned.
@@ -488,10 +489,12 @@ impl Handle {
         F: crate::future::Future + 'static,
         F::Output: 'static,
     {
-        let (handle, notified) = me
-            .shared
-            .owned
-            .bind_local(future, me.clone(), id, spawned_at);
+        // Safety: the caller guarantees that the this is only called on a `LocalRuntime`.
+        let (handle, notified) = unsafe {
+            me.shared
+                .owned
+                .bind_local(future, me.clone(), id, spawned_at)
+        };
 
         me.task_hooks.spawn(&TaskMeta {
             id,

tokio/src/runtime/scheduler/inject/rt_multi_thread.rs

@@ -55,13 +55,21 @@ impl<T: 'static> Shared<T> {
 
         // Now that the tasks are linked together, insert them into the
         // linked list.
-        self.push_batch_inner(shared, first, prev, counter);
+        //
+        // Safety: exactly the same safety requirements as `push_batch` method.
+        unsafe {
+            self.push_batch_inner(shared, first, prev, counter);
+        }
     }
 
     /// Inserts several tasks that have been linked together into the queue.
     ///
     /// The provided head and tail may be the same task. In this case, a
     /// single task is inserted.
+    ///
+    /// # Safety
+    ///
+    /// Must be called with the same `Synced` instance returned by `Inject::new`
     #[inline]
     unsafe fn push_batch_inner<L>(
         &self,
@@ -82,7 +90,8 @@ impl<T: 'static> Shared<T> {
             let mut curr = Some(batch_head);
 
             while let Some(task) = curr {
-                curr = task.get_queue_next();
+                // Safety: exactly the same safety requirements as `push_batch_inner`.
+                curr = unsafe { task.get_queue_next() };
 
                 let _ = unsafe { task::Notified::<T>::from_raw(task) };
             }
@@ -106,7 +115,7 @@ impl<T: 'static> Shared<T> {
         //
         // safety: All updates to the len atomic are guarded by the mutex. As
         // such, a non-atomic load followed by a store is safe.
-        let len = self.len.unsync_load();
+        let len = unsafe { self.len.unsync_load() };
 
         self.len.store(len + num, Release);
     }

tokio/src/runtime/scheduler/inject/shared.rs

@@ -71,7 +71,7 @@ impl<T: 'static> Shared<T> {
         }
 
         // safety: only mutated with the lock held
-        let len = self.len.unsync_load();
+        let len = unsafe { self.len.unsync_load() };
         let task = task.into_raw();
 
         // The next pointer should already be null
@@ -95,7 +95,7 @@ impl<T: 'static> Shared<T> {
     ///
     /// Must be called with the same `Synced` instance returned by `Inject::new`
     pub(crate) unsafe fn pop(&self, synced: &mut Synced) -> Option<task::Notified<T>> {
-        self.pop_n(synced, 1).next()
+        unsafe { self.pop_n(synced, 1).next() }
     }
 
     /// Pop `n` values from the queue
@@ -110,7 +110,7 @@ impl<T: 'static> Shared<T> {
 
         // safety: All updates to the len atomic are guarded by the mutex. As
         // such, a non-atomic load followed by a store is safe.
-        let len = self.len.unsync_load();
+        let len = unsafe { self.len.unsync_load() };
         let n = cmp::min(n, len);
 
         // Decrement the count.

tokio/src/runtime/scheduler/mod.rs

@@ -133,6 +133,7 @@ cfg_rt! {
         /// Spawn a local task
         ///
         /// # Safety
+        ///
         /// This should only be called in `LocalRuntime` if the runtime has been verified to be owned
         /// by the current thread.
         #[allow(irrefutable_let_patterns)]
@@ -143,7 +144,8 @@ cfg_rt! {
             F::Output: 'static,
         {
             if let Handle::CurrentThread(h) = self {
-                current_thread::Handle::spawn_local(h, future, id, spawned_at)
+                // Safety: caller guarantees that this is a `LocalRuntime`.
+                unsafe { current_thread::Handle::spawn_local(h, future, id, spawned_at) }
             } else {
                 panic!("Only current_thread and LocalSet have spawn_local internals implemented")
             }

tokio/src/runtime/task/core.rs

@@ -9,6 +9,15 @@
 //! Make sure to consult the relevant safety section of each function before
 //! use.
 
+// It doesn't make sense to enforce `unsafe_op_in_unsafe_fn` for this module because
+//
+// * This module is doing the low-level task management that requires tons of unsafe
+//   operations.
+// * Excessive `unsafe {}` blocks hurt readability significantly.
+// TODO: replace with `#[expect(unsafe_op_in_unsafe_fn)]` after bumpping
+// the MSRV to 1.81.0.
+#![allow(unsafe_op_in_unsafe_fn)]
+
 use crate::future::Future;
 use crate::loom::cell::UnsafeCell;
 use crate::runtime::context;

tokio/src/runtime/task/list.rs

@@ -106,6 +106,7 @@ impl<S: 'static> OwnedTasks<S> {
     /// Bind a task that isn't safe to transfer across thread boundaries.
     ///
     /// # Safety
+    ///
     /// Only use this in `LocalRuntime` where the task cannot move
     pub(crate) unsafe fn bind_local<T>(
         &self,

tokio/src/runtime/task/mod.rs

@@ -398,8 +398,11 @@ impl<S: 'static> Task<S> {
         }
     }
 
+    /// # Safety
+    ///
+    /// `ptr` must be a valid pointer to a [`Header`].
     unsafe fn from_raw(ptr: NonNull<Header>) -> Task<S> {
-        Task::new(RawTask::from_raw(ptr))
+        unsafe { Task::new(RawTask::from_raw(ptr)) }
     }
 
     #[cfg(all(
@@ -479,8 +482,11 @@ impl<S: 'static> Notified<S> {
 }
 
 impl<S: 'static> Notified<S> {
+    /// # Safety
+    ///
+    /// [`RawTask::ptr`] must be a valid pointer to a [`Header`].
     pub(crate) unsafe fn from_raw(ptr: RawTask) -> Notified<S> {
-        Notified(Task::new(ptr))
+        Notified(unsafe { Task::new(ptr) })
     }
 }
 
@@ -597,11 +603,11 @@ unsafe impl<S> linked_list::Link for Task<S> {
     }
 
     unsafe fn from_raw(ptr: NonNull<Header>) -> Task<S> {
-        Task::from_raw(ptr)
+        unsafe { Task::from_raw(ptr) }
     }
 
     unsafe fn pointers(target: NonNull<Header>) -> NonNull<linked_list::Pointers<Header>> {
-        self::core::Trailer::addr_of_owned(Header::get_trailer(target))
+        unsafe { self::core::Trailer::addr_of_owned(Header::get_trailer(target)) }
     }
 }
 

tokio/src/runtime/task/raw.rs

@@ -1,3 +1,12 @@
+// It doesn't make sense to enforce `unsafe_op_in_unsafe_fn` for this module because
+//
+// * This module is doing the low-level task management that requires tons of unsafe
+//   operations.
+// * Excessive `unsafe {}` blocks hurt readability significantly.
+// TODO: replace with `#[expect(unsafe_op_in_unsafe_fn)]` after bumpping
+// the MSRV to 1.81.0.
+#![allow(unsafe_op_in_unsafe_fn)]
+
 use crate::future::Future;
 use crate::runtime::task::core::{Core, Trailer};
 use crate::runtime::task::{Cell, Harness, Header, Id, Schedule, State};
@@ -222,6 +231,9 @@ impl RawTask {
         RawTask { ptr }
     }
 
+    /// # Safety
+    ///
+    /// `ptr` must be a valid pointer to a [`Header`].
     pub(super) unsafe fn from_raw(ptr: NonNull<Header>) -> RawTask {
         RawTask { ptr }
     }

tokio/src/runtime/task/trace/mod.rs

@@ -82,14 +82,18 @@ impl Context {
     where
         F: FnOnce(&Self) -> R,
     {
-        crate::runtime::context::with_trace(f)
+        unsafe { crate::runtime::context::with_trace(f) }
     }
 
+    /// SAFETY: Callers of this function must ensure that trace frames always
+    /// form a valid linked list.
     unsafe fn with_current_frame<F, R>(f: F) -> R
     where
         F: FnOnce(&Cell<Option<NonNull<Frame>>>) -> R,
     {
-        Self::try_with_current(|context| f(&context.active_frame)).expect(FAIL_NO_THREAD_LOCAL)
+        unsafe {
+            Self::try_with_current(|context| f(&context.active_frame)).expect(FAIL_NO_THREAD_LOCAL)
+        }
     }
 
     fn with_current_collector<F, R>(f: F) -> R
@@ -313,7 +317,8 @@ cfg_rt_multi_thread! {
 
         // clear the injection queue
         let mut synced = synced.lock();
-        while let Some(notified) = injection.pop(&mut synced.inject) {
+        // Safety: exactly the same safety requirements as `trace_multi_thread` function.
+        while let Some(notified) = unsafe { injection.pop(&mut synced.inject) } {
             dequeued.push(notified);
         }
 

tokio/src/runtime/task/waker.rs

@@ -42,6 +42,9 @@ impl<S> ops::Deref for WakerRef<'_, S> {
 }
 
 cfg_trace! {
+    /// # Safety
+    ///
+    /// `$header` must be a valid pointer to a [`Header`].
     macro_rules! trace {
         ($header:expr, $op:expr) => {
             if let Some(id) = Header::get_tracing_id(&$header) {
@@ -65,31 +68,50 @@ cfg_not_trace! {
 }
 
 unsafe fn clone_waker(ptr: *const ()) -> RawWaker {
-    let header = NonNull::new_unchecked(ptr as *mut Header);
-    trace!(header, "waker.clone");
-    header.as_ref().state.ref_inc();
+    // Safety: `ptr` was created from a `Header` pointer in function `waker_ref`.
+    let header = unsafe { NonNull::new_unchecked(ptr as *mut Header) };
+    #[cfg_attr(not(all(tokio_unstable, feature = "tracing")), allow(unused_unsafe))]
+    unsafe {
+        trace!(header, "waker.clone");
+    }
+    unsafe { header.as_ref() }.state.ref_inc();
     raw_waker(header)
 }
 
 unsafe fn drop_waker(ptr: *const ()) {
-    let ptr = NonNull::new_unchecked(ptr as *mut Header);
-    trace!(ptr, "waker.drop");
-    let raw = RawTask::from_raw(ptr);
+    // Safety: `ptr` was created from a `Header` pointer in function `waker_ref`.
+    let ptr = unsafe { NonNull::new_unchecked(ptr as *mut Header) };
+    // TODO; replace to #[expect(unused_unsafe)] after bumping MSRV to 1.81.0.
+    #[cfg_attr(not(all(tokio_unstable, feature = "tracing")), allow(unused_unsafe))]
+    unsafe {
+        trace!(ptr, "waker.drop");
+    }
+    let raw = unsafe { RawTask::from_raw(ptr) };
     raw.drop_reference();
 }
 
 unsafe fn wake_by_val(ptr: *const ()) {
-    let ptr = NonNull::new_unchecked(ptr as *mut Header);
-    trace!(ptr, "waker.wake");
-    let raw = RawTask::from_raw(ptr);
+    // Safety: `ptr` was created from a `Header` pointer in function `waker_ref`.
+    let ptr = unsafe { NonNull::new_unchecked(ptr as *mut Header) };
+    // TODO; replace to #[expect(unused_unsafe)] after bumping MSRV to 1.81.0.
+    #[cfg_attr(not(all(tokio_unstable, feature = "tracing")), allow(unused_unsafe))]
+    unsafe {
+        trace!(ptr, "waker.wake");
+    }
+    let raw = unsafe { RawTask::from_raw(ptr) };
     raw.wake_by_val();
 }
 
 // Wake without consuming the waker
 unsafe fn wake_by_ref(ptr: *const ()) {
-    let ptr = NonNull::new_unchecked(ptr as *mut Header);
-    trace!(ptr, "waker.wake_by_ref");
-    let raw = RawTask::from_raw(ptr);
+    // Safety: `ptr` was created from a `Header` pointer in function `waker_ref`.
+    let ptr = unsafe { NonNull::new_unchecked(ptr as *mut Header) };
+    // TODO; replace to #[expect(unused_unsafe)] after bumping MSRV to 1.81.0.
+    #[cfg_attr(not(all(tokio_unstable, feature = "tracing")), allow(unused_unsafe))]
+    unsafe {
+        trace!(ptr, "waker.wake_by_ref");
+    }
+    let raw = unsafe { RawTask::from_raw(ptr) };
     raw.wake_by_ref();
 }
 

tokio/src/runtime/time/entry.rs

@@ -471,7 +471,7 @@ unsafe impl linked_list::Link for TimerShared {
     unsafe fn pointers(
         target: NonNull<Self::Target>,
     ) -> NonNull<linked_list::Pointers<Self::Target>> {
-        TimerShared::addr_of_pointers(target)
+        unsafe { TimerShared::addr_of_pointers(target) }
     }
 }
 
@@ -644,7 +644,9 @@ impl TimerHandle {
     /// SAFETY: The caller must ensure that the handle remains valid, the driver
     /// lock is held, and that the timer is not in any wheel linked lists.
     pub(super) unsafe fn set_expiration(&self, tick: u64) {
-        self.inner.as_ref().set_expiration(tick);
+        unsafe {
+            self.inner.as_ref().set_expiration(tick);
+        }
     }
 
     /// Attempts to mark this entry as pending. If the expiration time is after
@@ -657,14 +659,18 @@ impl TimerHandle {
     /// lock is held, and that the timer is not in any wheel linked lists.
     /// After returning Ok, the entry must be added to the pending list.
     pub(super) unsafe fn mark_pending(&self, not_after: u64) -> Result<(), u64> {
-        match self.inner.as_ref().state.mark_pending(not_after) {
+        match unsafe { self.inner.as_ref().state.mark_pending(not_after) } {
             Ok(()) => {
                 // mark this as being on the pending queue in registered_when
-                self.inner.as_ref().set_registered_when(STATE_DEREGISTERED);
+                unsafe {
+                    self.inner.as_ref().set_registered_when(STATE_DEREGISTERED);
+                }
                 Ok(())
             }
             Err(tick) => {
-                self.inner.as_ref().set_registered_when(tick);
+                unsafe {
+                    self.inner.as_ref().set_registered_when(tick);
+                }
                 Err(tick)
             }
         }
@@ -682,6 +688,6 @@ impl TimerHandle {
     /// SAFETY: The driver lock must be held while invoking this function, and
     /// the entry must not be in any wheel linked lists.
     pub(super) unsafe fn fire(self, completed_state: TimerResult) -> Option<Waker> {
-        self.inner.as_ref().state.fire(completed_state)
+        unsafe { self.inner.as_ref().state.fire(completed_state) }
     }
 }

tokio/src/runtime/time/wheel/level.rs

@@ -120,7 +120,7 @@ impl Level {
     }
 
     pub(crate) unsafe fn add_entry(&mut self, item: TimerHandle) {
-        let slot = slot_for(item.registered_when(), self.level);
+        let slot = slot_for(unsafe { item.registered_when() }, self.level);
 
         self.slot[slot].push_front(item);
 

tokio/src/runtime/time/wheel/mod.rs

@@ -91,7 +91,7 @@ impl Wheel {
         &mut self,
         item: TimerHandle,
     ) -> Result<u64, (TimerHandle, InsertError)> {
-        let when = item.sync_when();
+        let when = unsafe { item.sync_when() };
 
         if when <= self.elapsed {
             return Err((item, InsertError::Elapsed));

tokio/src/signal/reusable_box.rs

@@ -81,18 +81,21 @@ impl<T> ReusableBoxFuture<T> {
         F: Future<Output = T> + Send + 'static,
     {
         // Drop the existing future, catching any panics.
-        let result = panic::catch_unwind(AssertUnwindSafe(|| {
+        let result = panic::catch_unwind(AssertUnwindSafe(|| unsafe {
             ptr::drop_in_place(self.boxed.as_ptr());
         }));
 
         // Overwrite the future behind the pointer. This is safe because the
         // allocation was allocated with the same size and alignment as the type F.
         let self_ptr: *mut F = self.boxed.as_ptr() as *mut F;
-        ptr::write(self_ptr, future);
+        // SAFETY: The pointer is valid and the layout is exactly same.
+        unsafe {
+            ptr::write(self_ptr, future);
+        }
 
         // Update the vtable of self.boxed. The pointer is not null because we
         // just got it from self.boxed, which is not null.
-        self.boxed = NonNull::new_unchecked(self_ptr);
+        self.boxed = unsafe { NonNull::new_unchecked(self_ptr) };
 
         // If the old future's destructor panicked, resume unwinding.
         match result {

tokio/src/signal/windows/sys.rs

@@ -157,9 +157,9 @@ mod tests {
         if event_requires_infinite_sleep_in_handler(signum) {
             // Those events will enter an infinite loop in `handler`, so
             // we need to run them on a separate thread
-            std::thread::spawn(move || super::handler(signum));
+            std::thread::spawn(move || unsafe { super::handler(signum) });
         } else {
-            super::handler(signum);
+            unsafe { super::handler(signum) };
         }
     }
 

tokio/src/sync/batch_semaphore.rs

@@ -775,6 +775,6 @@ unsafe impl linked_list::Link for Waiter {
     }
 
     unsafe fn pointers(target: NonNull<Waiter>) -> NonNull<linked_list::Pointers<Waiter>> {
-        Waiter::addr_of_pointers(target)
+        unsafe { Waiter::addr_of_pointers(target) }
     }
 }

tokio/src/sync/broadcast.rs

@@ -1678,7 +1678,7 @@ unsafe impl linked_list::Link for Waiter {
     }
 
     unsafe fn pointers(target: NonNull<Waiter>) -> NonNull<linked_list::Pointers<Waiter>> {
-        Waiter::addr_of_pointers(target)
+        unsafe { Waiter::addr_of_pointers(target) }
     }
 }
 

tokio/src/sync/mpsc/block.rs

@@ -163,9 +163,15 @@ impl<T> Block<T> {
         }
 
         // Get the value
-        let value = self.values[offset].with(|ptr| ptr::read(ptr));
+        //
+        // Safety:
+        //
+        // 1. The caller guarantees that there is no concurrent access to the slot.
+        // 2. The `UnsafeCell` always give us a valid pointer to the value.
+        let value = self.values[offset].with(|ptr| unsafe { ptr::read(ptr) });
 
-        Some(Read::Value(value.assume_init()))
+        // Safety: the redy bit is set, so the value has been initialized.
+        Some(Read::Value(unsafe { value.assume_init() }))
     }
 
     /// Returns true if *this* block has a value in the given slot.
@@ -197,7 +203,10 @@ impl<T> Block<T> {
         let slot_offset = offset(slot_index);
 
         self.values[slot_offset].with_mut(|ptr| {
-            ptr::write(ptr, MaybeUninit::new(value));
+            // Safety: the caller guarantees that there is no concurrent access to the slot
+            unsafe {
+                ptr::write(ptr, MaybeUninit::new(value));
+            }
         });
 
         // Release the value. After this point, the slot ref may no longer
@@ -246,7 +255,11 @@ impl<T> Block<T> {
         // tail_position is guaranteed to not access this block.
         self.header
             .observed_tail_position
-            .with_mut(|ptr| *ptr = tail_position);
+            // Safety:
+            //
+            // 1. The caller guarantees unique access to the block.
+            // 2. The `UnsafeCell` always gives us a valid pointer.
+            .with_mut(|ptr| unsafe { *ptr = tail_position });
 
         // Set the released bit, signalling to the receiver that it is safe to
         // free the block's memory as soon as all slots **prior** to
@@ -316,7 +329,9 @@ impl<T> Block<T> {
         success: Ordering,
         failure: Ordering,
     ) -> Result<(), NonNull<Block<T>>> {
-        block.as_mut().header.start_index = self.header.start_index.wrapping_add(BLOCK_CAP);
+        // Safety: caller guarantees that `block` is valid.
+        unsafe { block.as_mut() }.header.start_index =
+            self.header.start_index.wrapping_add(BLOCK_CAP);
 
         let next_ptr = self
             .header
@@ -428,8 +443,9 @@ impl<T> Values<T> {
         if_loom! {
             let p = _value.as_ptr() as *mut UnsafeCell<MaybeUninit<T>>;
             for i in 0..BLOCK_CAP {
-                p.add(i)
-                    .write(UnsafeCell::new(MaybeUninit::uninit()));
+                unsafe {
+                    p.add(i).write(UnsafeCell::new(MaybeUninit::uninit()));
+                }
             }
         }
     }

tokio/src/sync/mpsc/list.rs

@@ -184,6 +184,13 @@ impl<T> Tx<T> {
         }
     }
 
+    /// # Safety
+    ///
+    /// Behavior is undefined if any of the following conditions are violated:
+    ///
+    /// - The `block` was created by [`Box::into_raw`].
+    /// - The `block` is not currently part of any linked list.
+    /// - The `block` is a valid pointer to a [`Block<T>`].
     pub(crate) unsafe fn reclaim_block(&self, mut block: NonNull<Block<T>>) {
         // The block has been removed from the linked list and ownership
         // is reclaimed.
@@ -192,24 +199,28 @@ impl<T> Tx<T> {
         // inserting it back at the end of the linked list.
         //
         // First, reset the data
-        block.as_mut().reclaim();
+        //
+        // Safety: caller guarantees the block is valid and not in any list.
+        unsafe {
+            block.as_mut().reclaim();
+        }
 
         let mut reused = false;
 
         // Attempt to insert the block at the end
         //
         // Walk at most three times
-        //
         let curr_ptr = self.block_tail.load(Acquire);
 
         // The pointer can never be null
         debug_assert!(!curr_ptr.is_null());
 
-        let mut curr = NonNull::new_unchecked(curr_ptr);
+        // Safety: curr_ptr is never null.
+        let mut curr = unsafe { NonNull::new_unchecked(curr_ptr) };
 
         // TODO: Unify this logic with Block::grow
         for _ in 0..3 {
-            match curr.as_ref().try_push(&mut block, AcqRel, Acquire) {
+            match unsafe { curr.as_ref().try_push(&mut block, AcqRel, Acquire) } {
                 Ok(()) => {
                     reused = true;
                     break;
@@ -221,7 +232,11 @@ impl<T> Tx<T> {
         }
 
         if !reused {
-            let _ = Box::from_raw(block.as_ptr());
+            // Safety:
+            //
+            // 1. Caller guarantees the block is valid and not in any list.
+            // 2. The block was created by `Box::into_raw`.
+            let _ = unsafe { Box::from_raw(block.as_ptr()) };
         }
     }
 
@@ -387,8 +402,8 @@ impl<T> Rx<T> {
         }
 
         while let Some(block) = cur {
-            cur = block.as_ref().load_next(Relaxed);
-            drop(Box::from_raw(block.as_ptr()));
+            cur = unsafe { block.as_ref() }.load_next(Relaxed);
+            drop(unsafe { Box::from_raw(block.as_ptr()) });
         }
     }
 }

tokio/src/sync/notify.rs

@@ -1385,7 +1385,7 @@ unsafe impl linked_list::Link for Waiter {
     }
 
     unsafe fn pointers(target: NonNull<Waiter>) -> NonNull<linked_list::Pointers<Waiter>> {
-        Waiter::addr_of_pointers(target)
+        unsafe { Waiter::addr_of_pointers(target) }
     }
 }
 

tokio/src/sync/once_cell.rs

@@ -244,12 +244,16 @@ impl<T> OnceCell<T> {
 
     // SAFETY: The OnceCell must not be empty.
     unsafe fn get_unchecked(&self) -> &T {
-        &*self.value.with(|ptr| (*ptr).as_ptr())
+        unsafe { &*self.value.with(|ptr| (*ptr).as_ptr()) }
     }
 
     // SAFETY: The OnceCell must not be empty.
     unsafe fn get_unchecked_mut(&mut self) -> &mut T {
-        &mut *self.value.with_mut(|ptr| (*ptr).as_mut_ptr())
+        // SAFETY:
+        //
+        // 1. The caller guarantees that the OnceCell is initialized.
+        // 2. The `&mut self` guarantees that there are no other references to the value.
+        unsafe { &mut *self.value.with_mut(|ptr| (*ptr).as_mut_ptr()) }
     }
 
     fn set_value(&self, value: T, permit: SemaphorePermit<'_>) -> &T {

tokio/src/sync/oneshot.rs

@@ -404,31 +404,51 @@ struct Inner<T> {
 struct Task(UnsafeCell<MaybeUninit<Waker>>);
 
 impl Task {
+    /// # Safety
+    ///
+    /// The caller must do the necessary synchronization to ensure that
+    /// the [`Self::0`] contains the valid [`Waker`] during the call.
     unsafe fn will_wake(&self, cx: &mut Context<'_>) -> bool {
-        self.with_task(|w| w.will_wake(cx.waker()))
+        unsafe { self.with_task(|w| w.will_wake(cx.waker())) }
     }
 
+    /// # Safety
+    ///
+    /// The caller must do the necessary synchronization to ensure that
+    /// the [`Self::0`] contains the valid [`Waker`] during the call.
     unsafe fn with_task<F, R>(&self, f: F) -> R
     where
         F: FnOnce(&Waker) -> R,
     {
         self.0.with(|ptr| {
-            let waker: *const Waker = (*ptr).as_ptr();
-            f(&*waker)
+            let waker: *const Waker = unsafe { (*ptr).as_ptr() };
+            f(unsafe { &*waker })
         })
     }
 
+    /// # Safety
+    ///
+    /// The caller must do the necessary synchronization to ensure that
+    /// the [`Self::0`] contains the valid [`Waker`] during the call.
     unsafe fn drop_task(&self) {
         self.0.with_mut(|ptr| {
-            let ptr: *mut Waker = (*ptr).as_mut_ptr();
-            ptr.drop_in_place();
+            let ptr: *mut Waker = unsafe { (*ptr).as_mut_ptr() };
+            unsafe {
+                ptr.drop_in_place();
+            }
         });
     }
 
+    /// # Safety
+    ///
+    /// The caller must do the necessary synchronization to ensure that
+    /// the [`Self::0`] contains the valid [`Waker`] during the call.
     unsafe fn set_task(&self, cx: &mut Context<'_>) {
         self.0.with_mut(|ptr| {
-            let ptr: *mut Waker = (*ptr).as_mut_ptr();
-            ptr.write(cx.waker().clone());
+            let ptr: *mut Waker = unsafe { (*ptr).as_mut_ptr() };
+            unsafe {
+                ptr.write(cx.waker().clone());
+            }
         });
     }
 }
@@ -1377,7 +1397,7 @@ impl<T> Inner<T> {
     /// If `VALUE_SENT` is not set, then only the sender may call this method;
     /// if it is set, then only the receiver may call this method.
     unsafe fn consume_value(&self) -> Option<T> {
-        self.value.with_mut(|ptr| (*ptr).take())
+        self.value.with_mut(|ptr| unsafe { (*ptr).take() })
     }
 
     /// Returns true if there is a value. This function does not check `state`.
@@ -1390,7 +1410,7 @@ impl<T> Inner<T> {
     /// If `VALUE_SENT` is not set, then only the sender may call this method;
     /// if it is set, then only the receiver may call this method.
     unsafe fn has_value(&self) -> bool {
-        self.value.with(|ptr| (*ptr).is_some())
+        self.value.with(|ptr| unsafe { (*ptr).is_some() })
     }
 }
 

tokio/src/sync/set_once.rs

@@ -255,7 +255,7 @@ impl<T> SetOnce<T> {
 
     // SAFETY: The SetOnce must not be empty.
     unsafe fn get_unchecked(&self) -> &T {
-        &*self.value.with(|ptr| (*ptr).as_ptr())
+        unsafe { &*self.value.with(|ptr| (*ptr).as_ptr()) }
     }
 
     /// Returns a reference to the value currently stored in the `SetOnce`, or

tokio/src/sync/tests/notify.rs

@@ -12,15 +12,17 @@ fn notify_clones_waker_before_lock() {
 
     unsafe fn clone_w(data: *const ()) -> RawWaker {
         let ptr = data as *const Notify;
-        Arc::<Notify>::increment_strong_count(ptr);
+        unsafe {
+            Arc::<Notify>::increment_strong_count(ptr);
+        }
         // Or some other arbitrary code that shouldn't be executed while the
         // Notify wait list is locked.
-        (*ptr).notify_one();
+        unsafe { (*ptr).notify_one() };
         RawWaker::new(data, VTABLE)
     }
 
     unsafe fn drop_w(data: *const ()) {
-        drop(Arc::<Notify>::from_raw(data as *const Notify));
+        drop(unsafe { Arc::<Notify>::from_raw(data as *const Notify) });
     }
 
     unsafe fn wake(_data: *const ()) {

tokio/src/task/local.rs

@@ -1192,28 +1192,43 @@ impl task::Schedule for Arc<Shared> {
 }
 
 impl LocalState {
+    /// # Safety
+    ///
+    /// This method must only be called from the thread who
+    /// has the same [`ThreadId`] as [`Self::owner`].
     unsafe fn task_pop_front(&self) -> Option<task::Notified<Arc<Shared>>> {
         // The caller ensures it is called from the same thread that owns
         // the LocalSet.
         self.assert_called_from_owner_thread();
 
-        self.local_queue.with_mut(|ptr| (*ptr).pop_front())
+        self.local_queue
+            .with_mut(|ptr| unsafe { (*ptr).pop_front() })
     }
 
+    /// # Safety
+    ///
+    /// This method must only be called from the thread who
+    /// has the same [`ThreadId`] as [`Self::owner`].
     unsafe fn task_push_back(&self, task: task::Notified<Arc<Shared>>) {
         // The caller ensures it is called from the same thread that owns
         // the LocalSet.
         self.assert_called_from_owner_thread();
 
-        self.local_queue.with_mut(|ptr| (*ptr).push_back(task));
+        self.local_queue
+            .with_mut(|ptr| unsafe { (*ptr).push_back(task) });
     }
 
+    /// # Safety
+    ///
+    /// This method must only be called from the thread who
+    /// has the same [`ThreadId`] as [`Self::owner`].
     unsafe fn take_local_queue(&self) -> VecDeque<task::Notified<Arc<Shared>>> {
         // The caller ensures it is called from the same thread that owns
         // the LocalSet.
         self.assert_called_from_owner_thread();
 
-        self.local_queue.with_mut(|ptr| std::mem::take(&mut (*ptr)))
+        self.local_queue
+            .with_mut(|ptr| std::mem::take(unsafe { &mut (*ptr) }))
     }
 
     unsafe fn task_remove(&self, task: &Task<Arc<Shared>>) -> Option<Task<Arc<Shared>>> {

tokio/src/util/idle_notified_set.rs

@@ -349,7 +349,10 @@ impl<T> IdleNotifiedSet<T> {
 unsafe fn move_to_new_list<T>(from: &mut LinkedList<T>, to: &mut LinkedList<T>) {
     while let Some(entry) = from.pop_back() {
         entry.my_list.with_mut(|ptr| {
-            *ptr = List::Neither;
+            // Safety: pointer is accessed while holding the mutex.
+            unsafe {
+                *ptr = List::Neither;
+            }
         });
         to.push_front(entry);
     }
@@ -479,13 +482,13 @@ unsafe impl<T> linked_list::Link for ListEntry<T> {
     }
 
     unsafe fn from_raw(ptr: NonNull<ListEntry<T>>) -> Arc<ListEntry<T>> {
-        Arc::from_raw(ptr.as_ptr())
+        unsafe { Arc::from_raw(ptr.as_ptr()) }
     }
 
     unsafe fn pointers(
         target: NonNull<ListEntry<T>>,
     ) -> NonNull<linked_list::Pointers<ListEntry<T>>> {
-        ListEntry::addr_of_pointers(target)
+        unsafe { ListEntry::addr_of_pointers(target) }
     }
 }
 

tokio/src/util/linked_list.rs

@@ -1,4 +1,11 @@
 #![cfg_attr(not(feature = "full"), allow(dead_code))]
+// It doesn't make sense to enforce `unsafe_op_in_unsafe_fn` for this module because
+//
+// * The intrusive linked list naturally relies on unsafe operations.
+// * Excessive `unsafe {}` blocks hurt readability significantly.
+// TODO: replace with `#[expect(unsafe_op_in_unsafe_fn)]` after bumpping
+// the MSRV to 1.81.0.
+#![allow(unsafe_op_in_unsafe_fn)]
 
 //! An intrusive double linked list of data.
 //!
@@ -64,6 +71,8 @@ pub(crate) unsafe trait Link {
     /// stack as the argument. In particular, the method may not create an
     /// intermediate reference in the process of creating the resulting raw
     /// pointer.
+    ///
+    /// The `target` pointer must be valid.
     unsafe fn pointers(target: NonNull<Self::Target>) -> NonNull<Pointers<Self::Target>>;
 }
 

tokio/src/util/rc_cell.rs

@@ -35,7 +35,7 @@ impl<T> RcCell<T> {
         // not called recursively. Finally, this is the only place that can
         // create mutable references to the inner Rc. This ensures that any
         // mutable references created here are exclusive.
-        self.inner.with_mut(|ptr| f(&mut *ptr))
+        self.inner.with_mut(|ptr| f(unsafe { &mut *ptr }))
     }
 
     pub(crate) fn get(&self) -> Option<Rc<T>> {

tokio/src/util/sharded_list.rs

@@ -27,6 +27,7 @@ pub(crate) struct ShardedList<L, T> {
 /// call to call.
 pub(crate) unsafe trait ShardedListItem: Link {
     /// # Safety
+    ///
     /// The provided pointer must point at a valid list item.
     unsafe fn get_shard_id(target: NonNull<Self::Target>) -> usize;
 }
@@ -79,7 +80,7 @@ impl<L: ShardedListItem> ShardedList<L, L::Target> {
     /// - `node` is not contained by any list,
     /// - `node` is currently contained by some other `GuardedLinkedList`.
     pub(crate) unsafe fn remove(&self, node: NonNull<L::Target>) -> Option<L::Handle> {
-        let id = L::get_shard_id(node);
+        let id = unsafe { L::get_shard_id(node) };
         let mut lock = self.shard_inner(id);
         // SAFETY: Since the shard id cannot change, it's not possible for this node
         // to be in any other list of the same sharded list.

tokio/src/util/typeid.rs

@@ -9,7 +9,8 @@ use std::{
 pub(super) unsafe fn try_transmute<Src, Target: 'static>(x: Src) -> Result<Target, Src> {
     if nonstatic_typeid::<Src>() == TypeId::of::<Target>() {
         let x = ManuallyDrop::new(x);
-        Ok(mem::transmute_copy::<Src, Target>(&x))
+        // SAFETY: we have checked that the types are the same.
+        Ok(unsafe { mem::transmute_copy::<Src, Target>(&x) })
     } else {
         Err(x)
     }

tokio/src/util/wake.rs

@@ -51,22 +51,28 @@ fn waker_vtable<W: Wake>() -> &'static RawWakerVTable {
 }
 
 unsafe fn clone_arc_raw<T: Wake>(data: *const ()) -> RawWaker {
-    Arc::<T>::increment_strong_count(data as *const T);
+    // Safety: `data` was created from an `Arc::as_ptr` in function `waker_ref`.
+    unsafe {
+        Arc::<T>::increment_strong_count(data as *const T);
+    }
     RawWaker::new(data, waker_vtable::<T>())
 }
 
 unsafe fn wake_arc_raw<T: Wake>(data: *const ()) {
-    let arc: Arc<T> = Arc::from_raw(data as *const T);
+    // Safety: `data` was created from an `Arc::as_ptr` in function `waker_ref`.
+    let arc: Arc<T> = unsafe { Arc::from_raw(data as *const T) };
     Wake::wake(arc);
 }
 
 // used by `waker_ref`
 unsafe fn wake_by_ref_arc_raw<T: Wake>(data: *const ()) {
     // Retain Arc, but don't touch refcount by wrapping in ManuallyDrop
-    let arc = ManuallyDrop::new(Arc::<T>::from_raw(data.cast()));
+    // Safety: `data` was created from an `Arc::as_ptr` in function `waker_ref`.
+    let arc = ManuallyDrop::new(unsafe { Arc::<T>::from_raw(data.cast()) });
     Wake::wake_by_ref(&arc);
 }
 
 unsafe fn drop_arc_raw<T: Wake>(data: *const ()) {
-    drop(Arc::<T>::from_raw(data.cast()));
+    // Safety: `data` was created from an `Arc::as_ptr` in function `waker_ref`.
+    drop(unsafe { Arc::<T>::from_raw(data.cast()) });
 }