[PATCH v2 0/5] rust: sync: add WaitQueue infrastructure

[PATCH v2 0/5] rust: sync: add WaitQueue infrastructure

[Danilo Krummrich]

Add a WaitQueue abstraction wrapping struct wait_queue_head, providing
wait_event()-style methods that take a condition closure directly.

This is needed for a (subsequent) DRM patch series to wait for in-flight file
close operations during driver unbind. The Tyr driver also needs it for "CSF
firmware responses and other GPU-driven events" [1].

Convert CondVar (and PollCondVar) to use WaitQueue internally, removing
duplicate code using WaitQueue as the base primitive and add
wait_interruptible_freezable_nonexclusive() for subsequent binder usage.

Changes in v2:
- Drop the already merged workqueue patch.
- Make as_raw() public.
- Split error types and use bindings constants for direct C calls.
- Avoid condition rechecks after success.
- Check the condition before preparing a waiter.
- Add non-exclusive wait support, including a CondVar method for subsequent
  Binder conversion.
- Handle zero and expired timeouts before interruption; extend KUnit coverage.

[1] https://lore.kernel.org/dri-devel/20260721151423.444175-2-laura.nao@collabora.com/

Danilo Krummrich (5):
  rust: task: add safe schedule_timeout() wrapper
  rust: sync: add WaitQueue infrastructure
  rust: sync: convert CondVar and PollCondVar to use WaitQueue
  rust: sync: condvar: use task::schedule_timeout()
  rust: sync: condvar: add non-exclusive freezable waiting

 rust/kernel/sync.rs         |   8 +
 rust/kernel/sync/condvar.rs | 134 ++++-----
 rust/kernel/sync/poll.rs    |  19 +-
 rust/kernel/sync/wait.rs    | 524 ++++++++++++++++++++++++++++++++++++
 rust/kernel/task.rs         |  16 ++
 5 files changed, 612 insertions(+), 89 deletions(-)
 create mode 100644 rust/kernel/sync/wait.rs


base-commit: 41871f4ddf710339863f957bcfcab5094c234771
-- 
2.56.0

[PATCH v2 1/5] rust: task: add safe schedule_timeout() wrapper

[Danilo Krummrich]

Add a safe wrapper around schedule_timeout() that takes and returns
Jiffies, handling the c_long conversion internally.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/task.rs | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
index 3336df493dec..a733816fd5dd 100644
--- a/rust/kernel/task.rs
+++ b/rust/kernel/task.rs
@@ -10,6 +10,7 @@
     pid_namespace::PidNamespace,
     prelude::*,
     sync::aref::ARef,
+    time::Jiffies,
     types::{NotThreadSafe, Opaque},
 };
 use core::{
@@ -20,6 +21,21 @@
 /// A sentinel value used for infinite timeouts.
 pub const MAX_SCHEDULE_TIMEOUT: c_long = c_long::MAX;
 
+/// Sleeps for the given timeout in [`Jiffies`], or until woken.
+///
+/// Returns the remaining time in [`Jiffies`], or zero if the timeout expired.  The task state
+/// should be set before calling this.
+///
+/// Timeouts at or above [`MAX_SCHEDULE_TIMEOUT`] mean an indefinite wait. In that case, the return
+/// value is `MAX_SCHEDULE_TIMEOUT` as [`Jiffies`].
+#[inline]
+pub fn schedule_timeout(timeout: Jiffies) -> Jiffies {
+    let timeout = timeout.try_into().unwrap_or(MAX_SCHEDULE_TIMEOUT);
+
+    // SAFETY: `schedule_timeout()` is always safe to call.
+    unsafe { bindings::schedule_timeout(timeout) as Jiffies }
+}
+
 /// Bitmask for tasks that are sleeping in an interruptible state.
 pub const TASK_INTERRUPTIBLE: c_int = bindings::TASK_INTERRUPTIBLE as c_int;
 /// Bitmask for tasks that are sleeping in an uninterruptible state.
-- 
2.56.0

Re: [PATCH v2 1/5] rust: task: add safe schedule_timeout() wrapper

[FUJITA Tomonori]

On Thu,  5 Nov 2026 01:59:38 +0100
Danilo Krummrich <dakr@kernel.org> wrote:

> Add a safe wrapper around schedule_timeout() that takes and returns
> Jiffies, handling the c_long conversion internally.
> 
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

[...]

> +/// Sleeps for the given timeout in [`Jiffies`], or until woken.
> +///
> +/// Returns the remaining time in [`Jiffies`], or zero if the timeout expired.  The task state
> +/// should be set before calling this.
> +///
> +/// Timeouts at or above [`MAX_SCHEDULE_TIMEOUT`] mean an indefinite wait. In that case, the return
> +/// value is `MAX_SCHEDULE_TIMEOUT` as [`Jiffies`].
> +#[inline]
> +pub fn schedule_timeout(timeout: Jiffies) -> Jiffies {
> +    let timeout = timeout.try_into().unwrap_or(MAX_SCHEDULE_TIMEOUT);

The Jiffies alias will be removed, so could you use Delta<Jiffy> here
instead? I think the code would be almost the same as in my patch that
converts condvar [1].

This series conflicts with that patch. Boqun, how would you like to
merge them?

[1] https://lore.kernel.org/rust-for-linux/20261104235929.1282640-1-tomo@flapping.org/

[PATCH v2 2/5] rust: sync: add WaitQueue infrastructure

[Danilo Krummrich]

Implement a wait queue wrapping the kernel's struct wait_queue_head,
with wait_event()-style methods that take a condition closure directly.

The API mirrors the C wait_event() family:

  - wait_event()
  - wait_event_interruptible()
  - wait_event_timeout()
  - wait_event_interruptible_timeout()
  - wake_up() / wake_up_all() / wake_up_sync()

The interruptible variant returns Result<(), Interrupted>, the timeout
variant Result<(), TimedOut>, and the combined variant Result<(),
WaitError>. These errors map to ERESTARTSYS (signal) or ETIMEDOUT
(timeout).

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/sync.rs      |   8 +
 rust/kernel/sync/wait.rs | 527 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 535 insertions(+)
 create mode 100644 rust/kernel/sync/wait.rs

diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
index ee372c048a8a..5f7ffd828259 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -19,6 +19,7 @@
 mod refcount;
 mod set_once;
 pub mod srcu;
+mod wait;
 
 pub use arc::{Arc, ArcBorrow, UniqueArc};
 pub use completion::Completion;
@@ -41,3 +42,10 @@
 pub use refcount::Refcount;
 pub use set_once::SetOnce;
 pub use srcu::Srcu;
+pub use wait::{
+    new_waitqueue,
+    Interrupted,
+    TimedOut,
+    WaitError,
+    WaitQueue, //
+};
diff --git a/rust/kernel/sync/wait.rs b/rust/kernel/sync/wait.rs
new file mode 100644
index 000000000000..00120dbb4fca
--- /dev/null
+++ b/rust/kernel/sync/wait.rs
@@ -0,0 +1,527 @@
+// SPDX-License-Identifier: GPL-2.0
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+
+//! Wait queue.
+//!
+//! C header: [`include/linux/wait.h`](srctree/include/linux/wait.h)
+
+use super::LockClassKey;
+use crate::{
+    prelude::*,
+    str::CStr,
+    task,
+    time::Jiffies,
+    types::Opaque, //
+};
+
+use core::{
+    pin::Pin,
+    ptr, //
+};
+
+/// Creates a [`WaitQueue`] initialiser with the given name and a newly-created lock class.
+#[macro_export]
+macro_rules! new_waitqueue {
+    ($($name:literal)?) => {
+        $crate::sync::WaitQueue::new(
+            $crate::optional_name!($($name)?),
+            $crate::static_lock_class!(),
+        )
+    };
+}
+pub use new_waitqueue;
+
+/// Exposes the kernel's [`struct wait_queue_head`] as a Rust wait queue.
+///
+/// A `WaitQueue` allows a thread to sleep until a caller-supplied condition becomes true,
+/// re-checking the condition on each wake-up. This matches the C `wait_event()` family of macros.
+///
+/// For waiting with a lock guard (the condition variable pattern), use [`CondVar`](super::CondVar)
+/// instead.
+///
+/// Instances of `WaitQueue` need a lock class and to be pinned. The recommended way to create such
+/// instances is with the [`pin_init!`] and [`new_waitqueue!`] macros.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::sync::{
+///     atomic::{
+///         Atomic,
+///         Relaxed,
+///     },
+///     new_waitqueue,
+///     WaitQueue,
+/// };
+///
+/// #[pin_data]
+/// pub struct Example {
+///     value: Atomic<i32>,
+///     #[pin]
+///     queue: WaitQueue,
+/// }
+///
+/// fn wait_for_value(e: &Example, v: i32) {
+///     e.queue.wait_event(|| e.value.load(Relaxed) == v);
+/// }
+///
+/// fn set_value(e: &Example, v: i32) {
+///     e.value.store(v, Relaxed);
+///     e.queue.wake_up();
+/// }
+/// ```
+///
+/// [`struct wait_queue_head`]: srctree/include/linux/wait.h
+#[pin_data]
+pub struct WaitQueue {
+    #[pin]
+    wait_queue_head: Opaque<bindings::wait_queue_head>,
+}
+
+// SAFETY: `WaitQueue` only uses a `struct wait_queue_head`, which is safe to use on any thread.
+unsafe impl Send for WaitQueue {}
+
+// SAFETY: `WaitQueue` only uses a `struct wait_queue_head`, which is safe to use on multiple
+// threads concurrently.
+unsafe impl Sync for WaitQueue {}
+
+impl WaitQueue {
+    /// Constructs a new wait queue initialiser.
+    pub fn new(name: &'static CStr, key: Pin<&'static LockClassKey>) -> impl PinInit<Self> {
+        pin_init!(Self {
+            // SAFETY: `slot` is valid while the closure is called and both `name` and `key` have
+            // static lifetimes so they live indefinitely.
+            wait_queue_head <- Opaque::ffi_init(|slot| unsafe {
+                bindings::__init_waitqueue_head(slot, name.as_char_ptr(), key.as_ptr())
+            }),
+        })
+    }
+
+    /// Returns a raw pointer to the underlying `wait_queue_head`.
+    #[inline]
+    pub fn as_raw(&self) -> *mut bindings::wait_queue_head {
+        self.wait_queue_head.get()
+    }
+
+    /// Sleeps until the condition returns `true`.
+    ///
+    /// The condition is checked before each sleep and after each wake-up. The wait is
+    /// uninterruptible.
+    #[inline]
+    pub fn wait_event<F: FnMut() -> bool>(&self, condition: F) {
+        // An uninterruptible wait without a timeout cannot fail.
+        let _ =
+            self.wait_event_timeout_internal(task::TASK_UNINTERRUPTIBLE, condition, Jiffies::MAX);
+    }
+
+    /// Sleeps until the condition returns `true` or a signal is received.
+    ///
+    /// Returns `Ok(())` when the condition is met, or [`Interrupted`] if interrupted by a signal.
+    #[inline]
+    pub fn wait_event_interruptible<F: FnMut() -> bool>(
+        &self,
+        condition: F,
+    ) -> Result<(), Interrupted> {
+        // Without a timeout, interruption is the only possible error.
+        self.wait_event_timeout_internal(task::TASK_INTERRUPTIBLE, condition, Jiffies::MAX)
+            .map_err(|_| Interrupted)
+    }
+
+    /// Sleeps until the condition returns `true` or the timeout expires.
+    ///
+    /// Returns `Ok(())` when the condition is met, or [`TimedOut`] if the timeout elapsed first.
+    #[inline]
+    pub fn wait_event_timeout<F: FnMut() -> bool>(
+        &self,
+        condition: F,
+        jiffies: Jiffies,
+    ) -> Result<(), TimedOut> {
+        // An uninterruptible wait can only fail by timing out.
+        self.wait_event_timeout_internal(task::TASK_UNINTERRUPTIBLE, condition, jiffies)
+            .map_err(|_| TimedOut)
+    }
+
+    /// Sleeps until the condition returns `true`, a signal is received, or the timeout expires.
+    ///
+    /// Returns `Ok(())` when the condition is met, or [`WaitError`] on signal or timeout.
+    #[inline]
+    pub fn wait_event_interruptible_timeout<F: FnMut() -> bool>(
+        &self,
+        condition: F,
+        jiffies: Jiffies,
+    ) -> Result<(), WaitError> {
+        self.wait_event_timeout_internal(task::TASK_INTERRUPTIBLE, condition, jiffies)
+    }
+
+    fn wait_event_timeout_internal<F: FnMut() -> bool>(
+        &self,
+        wait_state: c_int,
+        mut condition: F,
+        jiffies: Jiffies,
+    ) -> Result<(), WaitError> {
+        if condition() {
+            return Ok(());
+        }
+
+        if jiffies == 0 {
+            return Err(TimedOut.into());
+        }
+
+        let wait = Opaque::<bindings::wait_queue_entry>::uninit();
+
+        // SAFETY: `wait` points to valid memory.
+        unsafe { bindings::init_wait(wait.get()) };
+
+        let mut remaining = jiffies;
+
+        let result = loop {
+            // SAFETY: Both pointers are valid, and `wait` was initialised by `init_wait()` above.
+            let ret = unsafe {
+                bindings::prepare_to_wait_event(self.wait_queue_head.get(), wait.get(), wait_state)
+            };
+
+            if condition() {
+                break Ok(());
+            }
+
+            if ret != 0 {
+                break Err(Interrupted.into());
+            }
+
+            remaining = task::schedule_timeout(remaining);
+
+            if condition() {
+                break Ok(());
+            }
+
+            if remaining == 0 {
+                break Err(TimedOut.into());
+            }
+        };
+
+        // SAFETY: Both pointers are valid, and `wait` is no longer used after this call.
+        unsafe { bindings::finish_wait(self.wait_queue_head.get(), wait.get()) };
+
+        result
+    }
+
+    /// Performs a single non-exclusive prepare-to-wait / finish-wait cycle, calling `schedule_fn`
+    /// in between. Non-exclusive waiters are all woken by [`wake_up()`](Self::wake_up).
+    #[inline]
+    #[expect(unused)]
+    pub(super) fn wait_once<F, R>(&self, wait_state: c_int, schedule_fn: F) -> R
+    where
+        F: FnOnce() -> R,
+    {
+        self.wait_once_internal(wait_state, false, schedule_fn)
+    }
+
+    /// Performs a single exclusive prepare-to-wait / finish-wait cycle, calling `schedule_fn`
+    /// in between.
+    #[inline]
+    #[expect(unused)]
+    pub(super) fn wait_once_exclusive<F, R>(&self, wait_state: c_int, schedule_fn: F) -> R
+    where
+        F: FnOnce() -> R,
+    {
+        self.wait_once_internal(wait_state, true, schedule_fn)
+    }
+
+    fn wait_once_internal<F, R>(&self, wait_state: c_int, exclusive: bool, schedule_fn: F) -> R
+    where
+        F: FnOnce() -> R,
+    {
+        let wait = Opaque::<bindings::wait_queue_entry>::uninit();
+
+        // SAFETY: `wait` points to valid memory.
+        unsafe { bindings::init_wait(wait.get()) };
+
+        // SAFETY: Both `wait` and `wait_queue_head` point to valid memory.
+        unsafe {
+            if exclusive {
+                bindings::prepare_to_wait_exclusive(
+                    self.wait_queue_head.get(),
+                    wait.get(),
+                    wait_state,
+                );
+            } else {
+                bindings::prepare_to_wait(self.wait_queue_head.get(), wait.get(), wait_state);
+            }
+        };
+
+        let ret = schedule_fn();
+
+        // SAFETY: Both `wait` and `wait_queue_head` point to valid memory.
+        unsafe { bindings::finish_wait(self.wait_queue_head.get(), wait.get()) };
+
+        ret
+    }
+
+    /// Wakes up waiters.
+    ///
+    /// Wakes all non-exclusive waiters and one exclusive waiter, if any.  Matches C's `wake_up()`.
+    #[inline]
+    pub fn wake_up(&self) {
+        // SAFETY: `wait_queue_head` points to valid memory.
+        unsafe {
+            bindings::__wake_up(
+                self.wait_queue_head.get(),
+                bindings::TASK_NORMAL,
+                1,
+                ptr::null_mut(),
+            )
+        };
+    }
+
+    /// Wakes up all waiters.
+    ///
+    /// Wakes all non-exclusive and all exclusive waiters, if any.
+    /// Matches C's `wake_up_all()`.
+    #[inline]
+    pub fn wake_up_all(&self) {
+        // SAFETY: `wait_queue_head` points to valid memory.
+        unsafe {
+            bindings::__wake_up(
+                self.wait_queue_head.get(),
+                bindings::TASK_NORMAL,
+                0,
+                ptr::null_mut(),
+            )
+        };
+    }
+
+    /// Like [`wake_up()`](Self::wake_up), but hints to the scheduler that the current task
+    /// expects to sleep soon. Matches C's `wake_up_sync()`.
+    #[inline]
+    pub fn wake_up_sync(&self) {
+        // SAFETY: `wait_queue_head` points to valid memory.
+        unsafe { bindings::__wake_up_sync(self.wait_queue_head.get(), bindings::TASK_NORMAL) };
+    }
+
+    /// Wakes up all waiters and clears poll registrations.
+    ///
+    /// Used when a wait queue is about to be freed, to ensure epoll items are properly removed.
+    /// Matches C's `wake_up_pollfree()`.
+    #[inline]
+    #[expect(unused)]
+    pub(super) fn wake_up_pollfree(&self) {
+        // SAFETY: `wait_queue_head` points to valid memory.
+        unsafe { bindings::__wake_up_pollfree(self.wait_queue_head.get()) };
+    }
+}
+
+/// A wait was interrupted by a signal.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct Interrupted;
+
+/// A wait timed out before its condition was met.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct TimedOut;
+
+impl From<Interrupted> for Error {
+    #[inline]
+    fn from(_: Interrupted) -> Error {
+        ERESTARTSYS
+    }
+}
+
+impl From<TimedOut> for Error {
+    #[inline]
+    fn from(_: TimedOut) -> Error {
+        ETIMEDOUT
+    }
+}
+
+/// Error returned by [`WaitQueue`] wait functions.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum WaitError {
+    /// Interrupted by a signal.
+    Signal,
+    /// The timeout elapsed without the condition being met.
+    Timeout,
+}
+
+impl From<Interrupted> for WaitError {
+    #[inline]
+    fn from(_: Interrupted) -> Self {
+        Self::Signal
+    }
+}
+
+impl From<TimedOut> for WaitError {
+    #[inline]
+    fn from(_: TimedOut) -> Self {
+        Self::Timeout
+    }
+}
+
+impl From<WaitError> for Error {
+    #[inline]
+    fn from(e: WaitError) -> Error {
+        match e {
+            WaitError::Signal => ERESTARTSYS,
+            WaitError::Timeout => ETIMEDOUT,
+        }
+    }
+}
+
+#[macros::kunit_tests(rust_waitqueue)]
+mod tests {
+    use super::*;
+    use crate::{
+        sync::{
+            atomic::{
+                Atomic,
+                Relaxed, //
+            },
+            Arc,
+        },
+        time::{
+            delay::fsleep,
+            Delta, //
+        },
+        workqueue,
+    };
+
+    #[pin_data]
+    struct State {
+        value: Atomic<i32>,
+        #[pin]
+        wq: WaitQueue,
+    }
+
+    impl State {
+        fn new() -> Result<Arc<Self>> {
+            Arc::pin_init(
+                pin_init!(Self {
+                    value: Atomic::new(0),
+                    wq <- new_waitqueue!(),
+                }),
+                GFP_KERNEL,
+            )
+        }
+    }
+
+    #[test]
+    fn wait_event_from_work() {
+        let s = State::new().unwrap();
+
+        let s2 = s.clone();
+        workqueue::system_dfl()
+            .try_spawn(GFP_KERNEL, move || {
+                s2.value.store(1, Relaxed);
+                s2.wq.wake_up();
+            })
+            .unwrap();
+
+        s.wq.wait_event(|| s.value.load(Relaxed) == 1);
+        assert_eq!(s.value.load(Relaxed), 1);
+    }
+
+    #[test]
+    fn wait_event_condition_already_true() {
+        let s = State::new().unwrap();
+        let mut calls = 0;
+
+        s.wq.wait_event(|| {
+            calls += 1;
+            true
+        });
+
+        assert_eq!(calls, 1);
+    }
+
+    #[test]
+    fn wait_event_condition_not_yet_met() {
+        let s = State::new().unwrap();
+
+        let s2 = s.clone();
+        workqueue::system_dfl()
+            .try_spawn(GFP_KERNEL, move || {
+                s2.value.store(1, Relaxed);
+                s2.wq.wake_up_all();
+
+                fsleep(Delta::from_millis(50));
+
+                s2.value.store(2, Relaxed);
+                s2.wq.wake_up_all();
+            })
+            .unwrap();
+
+        s.wq.wait_event(|| s.value.load(Relaxed) == 2);
+        assert_eq!(s.value.load(Relaxed), 2);
+    }
+
+    #[test]
+    fn wait_event_timeout_expires() {
+        let s = State::new().unwrap();
+
+        let ret = s.wq.wait_event_timeout(|| s.value.load(Relaxed) == 1, 1);
+        assert_eq!(ret, Err(TimedOut));
+    }
+
+    #[test]
+    fn wait_event_does_not_recheck_success() {
+        enum WaitKind {
+            Uninterruptible,
+            Interruptible,
+            Timeout,
+            InterruptibleTimeout,
+        }
+
+        let s = State::new().unwrap();
+
+        for kind in [
+            WaitKind::Uninterruptible,
+            WaitKind::Interruptible,
+            WaitKind::Timeout,
+            WaitKind::InterruptibleTimeout,
+        ] {
+            let mut calls = 0;
+            let condition = || {
+                // Bypass the initial fast path to exercise the wait loop.
+                calls += 1;
+                calls > 1
+            };
+
+            let ret = match kind {
+                WaitKind::Uninterruptible => {
+                    s.wq.wait_event(condition);
+                    Ok(())
+                }
+                WaitKind::Interruptible => {
+                    s.wq.wait_event_interruptible(condition).map_err(Into::into)
+                }
+                WaitKind::Timeout => s.wq.wait_event_timeout(condition, 1).map_err(Into::into),
+                WaitKind::InterruptibleTimeout => {
+                    s.wq.wait_event_interruptible_timeout(condition, 1)
+                }
+            };
+
+            assert_eq!(ret, Ok(()));
+            assert_eq!(calls, 2);
+        }
+    }
+
+    #[test]
+    fn wait_event_zero_timeout() {
+        let s = State::new().unwrap();
+
+        for interruptible in [false, true] {
+            let mut calls = 0;
+            let condition = || {
+                calls += 1;
+                false
+            };
+
+            let ret = if interruptible {
+                s.wq.wait_event_interruptible_timeout(condition, 0)
+            } else {
+                s.wq.wait_event_timeout(condition, 0).map_err(Into::into)
+            };
+
+            assert_eq!(ret, Err(WaitError::Timeout));
+            assert_eq!(calls, 1);
+        }
+    }
+}
-- 
2.56.0

[PATCH v2 3/5] rust: sync: convert CondVar and PollCondVar to use WaitQueue

[Danilo Krummrich]

CondVar currently wraps a raw wait_queue_head directly. Now that
WaitQueue provides the same primitive, convert CondVar to use it
instead. This removes duplicate init, pinning, Send/Sync, and wake-up
code from CondVar.

Keep the wait logic in CondVar since it needs to release and reacquire a
lock guard around the sleep, which WaitQueue's condition-based
wait_event() methods do not handle. Use wait_once_exclusive() to perform
a single prepare_to_wait_exclusive / finish_wait cycle with a
caller-provided schedule function to implement the lock-aware sleep.

Adapt PollCondVar accordingly.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/sync/condvar.rs | 89 +++++++++++--------------------------
 rust/kernel/sync/poll.rs    | 19 ++++----
 rust/kernel/sync/wait.rs    |  2 -
 3 files changed, 33 insertions(+), 77 deletions(-)

diff --git a/rust/kernel/sync/condvar.rs b/rust/kernel/sync/condvar.rs
index 69d58dfbad7b..78a5f10d68fa 100644
--- a/rust/kernel/sync/condvar.rs
+++ b/rust/kernel/sync/condvar.rs
@@ -5,18 +5,26 @@
 //! This module allows Rust code to use the kernel's [`struct wait_queue_head`] as a condition
 //! variable.
 
-use super::{lock::Backend, lock::Guard, LockClassKey};
+use super::{
+    lock::Backend,
+    lock::Guard,
+    LockClassKey,
+    WaitQueue, //
+};
+
 use crate::{
-    ffi::{c_int, c_long},
-    str::{CStr, CStrExt as _},
+    prelude::*,
+    str::CStr,
     task::{
-        MAX_SCHEDULE_TIMEOUT, TASK_FREEZABLE, TASK_INTERRUPTIBLE, TASK_NORMAL, TASK_UNINTERRUPTIBLE,
+        MAX_SCHEDULE_TIMEOUT,
+        TASK_FREEZABLE,
+        TASK_INTERRUPTIBLE,
+        TASK_UNINTERRUPTIBLE, //
     },
     time::Jiffies,
-    types::Opaque,
 };
-use core::{marker::PhantomPinned, pin::Pin, ptr};
-use pin_init::{pin_data, pin_init, PinInit};
+
+use core::pin::Pin;
 
 /// Creates a [`CondVar`] initialiser with the given name and a newly-created lock class.
 #[macro_export]
@@ -81,33 +89,14 @@ macro_rules! new_condvar {
 #[pin_data]
 pub struct CondVar {
     #[pin]
-    pub(crate) wait_queue_head: Opaque<bindings::wait_queue_head>,
-
-    /// A condvar needs to be pinned because it contains a [`struct list_head`] that is
-    /// self-referential, so it cannot be safely moved once it is initialised.
-    ///
-    /// [`struct list_head`]: srctree/include/linux/types.h
-    #[pin]
-    _pin: PhantomPinned,
+    pub(crate) wq: WaitQueue,
 }
 
-// SAFETY: `CondVar` only uses a `struct wait_queue_head`, which is safe to use on any thread.
-unsafe impl Send for CondVar {}
-
-// SAFETY: `CondVar` only uses a `struct wait_queue_head`, which is safe to use on multiple threads
-// concurrently.
-unsafe impl Sync for CondVar {}
-
 impl CondVar {
     /// Constructs a new condvar initialiser.
     pub fn new(name: &'static CStr, key: Pin<&'static LockClassKey>) -> impl PinInit<Self> {
         pin_init!(Self {
-            _pin: PhantomPinned,
-            // SAFETY: `slot` is valid while the closure is called and both `name` and `key` have
-            // static lifetimes so they live indefinitely.
-            wait_queue_head <- Opaque::ffi_init(|slot| unsafe {
-                bindings::__init_waitqueue_head(slot, name.as_char_ptr(), key.as_ptr())
-            }),
+            wq <- WaitQueue::new(name, key),
         })
     }
 
@@ -117,23 +106,10 @@ fn wait_internal<T: ?Sized, B: Backend>(
         guard: &mut Guard<'_, T, B>,
         timeout_in_jiffies: c_long,
     ) -> c_long {
-        let wait = Opaque::<bindings::wait_queue_entry>::uninit();
-
-        // SAFETY: `wait` points to valid memory.
-        unsafe { bindings::init_wait(wait.get()) };
-
-        // SAFETY: Both `wait` and `wait_queue_head` point to valid memory.
-        unsafe {
-            bindings::prepare_to_wait_exclusive(self.wait_queue_head.get(), wait.get(), wait_state)
-        };
-
-        // SAFETY: Switches to another thread. The timeout can be any number.
-        let ret = guard.do_unlocked(|| unsafe { bindings::schedule_timeout(timeout_in_jiffies) });
-
-        // SAFETY: Both `wait` and `wait_queue_head` point to valid memory.
-        unsafe { bindings::finish_wait(self.wait_queue_head.get(), wait.get()) };
-
-        ret
+        self.wq.wait_once_exclusive(wait_state, || {
+            // SAFETY: Switches to another thread. The timeout can be any number.
+            guard.do_unlocked(|| unsafe { bindings::schedule_timeout(timeout_in_jiffies) })
+        })
     }
 
     /// Releases the lock and waits for a notification in uninterruptible mode.
@@ -198,28 +174,13 @@ pub fn wait_interruptible_timeout<T: ?Sized, B: Backend>(
         }
     }
 
-    /// Calls the kernel function to notify the appropriate number of threads.
-    fn notify(&self, count: c_int) {
-        // SAFETY: `wait_queue_head` points to valid memory.
-        unsafe {
-            bindings::__wake_up(
-                self.wait_queue_head.get(),
-                TASK_NORMAL,
-                count,
-                ptr::null_mut(),
-            )
-        };
-    }
-
     /// Calls the kernel function to notify one thread synchronously.
     ///
     /// This method behaves like `notify_one`, except that it hints to the scheduler that the
-    /// current thread is about to go to sleep, so it should schedule the target thread on the same
-    /// CPU.
+    /// current thread expects to sleep soon.
     #[inline]
     pub fn notify_sync(&self) {
-        // SAFETY: `wait_queue_head` points to valid memory.
-        unsafe { bindings::__wake_up_sync(self.wait_queue_head.get(), TASK_NORMAL) };
+        self.wq.wake_up_sync();
     }
 
     /// Wakes a single waiter up, if any.
@@ -228,7 +189,7 @@ pub fn notify_sync(&self) {
     /// completely (as opposed to automatically waking up the next waiter).
     #[inline]
     pub fn notify_one(&self) {
-        self.notify(1);
+        self.wq.wake_up();
     }
 
     /// Wakes all waiters up, if any.
@@ -237,7 +198,7 @@ pub fn notify_one(&self) {
     /// completely (as opposed to automatically waking up the next waiter).
     #[inline]
     pub fn notify_all(&self) {
-        self.notify(0);
+        self.wq.wake_up_all();
     }
 }
 
diff --git a/rust/kernel/sync/poll.rs b/rust/kernel/sync/poll.rs
index dc40bfaa57e6..fbd754a0bc54 100644
--- a/rust/kernel/sync/poll.rs
+++ b/rust/kernel/sync/poll.rs
@@ -64,11 +64,11 @@ pub fn register_wait(&self, file: &File, cv: &PollCondVar) {
         // * `file.as_ptr()` references a valid file for the duration of this call.
         // * `self.table` is null or references a valid poll_table for the duration of this call.
         // * Since `PollCondVar` is pinned, its destructor is guaranteed to run before the memory
-        //   containing `cv.wait_queue_head` is invalidated. Since the destructor clears all
-        //   waiters and then waits for an rcu grace period, it's guaranteed that
-        //   `cv.wait_queue_head` remains valid for at least an rcu grace period after the removal
-        //   of the last waiter.
-        unsafe { bindings::poll_wait(file.as_ptr(), cv.wait_queue_head.get(), self.table) }
+        //   containing the wait queue head is invalidated. Since the destructor clears all
+        //   waiters and then waits for an rcu grace period, it's guaranteed that the wait queue
+        //   head remains valid for at least an rcu grace period after the removal of the last
+        //   waiter.
+        unsafe { bindings::poll_wait(file.as_ptr(), cv.wq.as_raw(), self.table) }
     }
 }
 
@@ -105,9 +105,7 @@ impl PinnedDrop for PollCondVar {
     #[inline]
     fn drop(self: Pin<&mut Self>) {
         // Clear anything registered using `register_wait`.
-        //
-        // SAFETY: The pointer points at a valid `wait_queue_head`.
-        unsafe { bindings::__wake_up_pollfree(self.inner.wait_queue_head.get()) };
+        self.inner.wq.wake_up_pollfree();
 
         // Wait for epoll items to be properly removed.
         synchronize_rcu();
@@ -165,14 +163,13 @@ fn drop(&mut self) {
         // SAFETY: ManuallyDrop::take ok because not already taken.
         let boxed = unsafe { ManuallyDrop::take(&mut self.inner) };
 
+        boxed.inner.inner.wq.wake_up_pollfree();
+
         // SAFETY: The code below frees the box without calling the actual destructor of the type,
         // but it's okay because it re-implements the destructor using `kfree_rcu()` in place of
         // `synchronize_rcu()`.
         let ptr = KBox::into_raw(unsafe { Pin::into_inner_unchecked(boxed) });
 
-        // SAFETY: The pointer points at a valid `wait_queue_head`.
-        unsafe { bindings::__wake_up_pollfree((*ptr).inner.inner.wait_queue_head.get()) };
-
         // SAFETY: This was allocated using `KBox::pin_init`, so it can be freed with `kvfree`.
         unsafe { bindings::kvfree_call_rcu((*ptr).rcu.get(), ptr.cast::<ffi::c_void>()) };
     }
diff --git a/rust/kernel/sync/wait.rs b/rust/kernel/sync/wait.rs
index 00120dbb4fca..92c1ae93705e 100644
--- a/rust/kernel/sync/wait.rs
+++ b/rust/kernel/sync/wait.rs
@@ -219,7 +219,6 @@ pub(super) fn wait_once<F, R>(&self, wait_state: c_int, schedule_fn: F) -> R
     /// Performs a single exclusive prepare-to-wait / finish-wait cycle, calling `schedule_fn`
     /// in between.
     #[inline]
-    #[expect(unused)]
     pub(super) fn wait_once_exclusive<F, R>(&self, wait_state: c_int, schedule_fn: F) -> R
     where
         F: FnOnce() -> R,
@@ -303,7 +302,6 @@ pub fn wake_up_sync(&self) {
     /// Used when a wait queue is about to be freed, to ensure epoll items are properly removed.
     /// Matches C's `wake_up_pollfree()`.
     #[inline]
-    #[expect(unused)]
     pub(super) fn wake_up_pollfree(&self) {
         // SAFETY: `wait_queue_head` points to valid memory.
         unsafe { bindings::__wake_up_pollfree(self.wait_queue_head.get()) };
-- 
2.56.0

[PATCH v2 4/5] rust: sync: condvar: use task::schedule_timeout()

[Danilo Krummrich]

Convert CondVar::wait_internal() from calling
bindings::schedule_timeout() directly to using the safe
task::schedule_timeout() wrapper. This removes the unsafe call and the
Jiffies-to-c_long conversion from CondVar, since the wrapper handles it.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/sync/condvar.rs | 24 +++++++++---------------
 1 file changed, 9 insertions(+), 15 deletions(-)

diff --git a/rust/kernel/sync/condvar.rs b/rust/kernel/sync/condvar.rs
index 78a5f10d68fa..fcab90f6ce34 100644
--- a/rust/kernel/sync/condvar.rs
+++ b/rust/kernel/sync/condvar.rs
@@ -16,7 +16,7 @@
     prelude::*,
     str::CStr,
     task::{
-        MAX_SCHEDULE_TIMEOUT,
+        self,
         TASK_FREEZABLE,
         TASK_INTERRUPTIBLE,
         TASK_UNINTERRUPTIBLE, //
@@ -104,11 +104,10 @@ fn wait_internal<T: ?Sized, B: Backend>(
         &self,
         wait_state: c_int,
         guard: &mut Guard<'_, T, B>,
-        timeout_in_jiffies: c_long,
-    ) -> c_long {
+        timeout: Jiffies,
+    ) -> Jiffies {
         self.wq.wait_once_exclusive(wait_state, || {
-            // SAFETY: Switches to another thread. The timeout can be any number.
-            guard.do_unlocked(|| unsafe { bindings::schedule_timeout(timeout_in_jiffies) })
+            guard.do_unlocked(|| task::schedule_timeout(timeout))
         })
     }
 
@@ -119,7 +118,7 @@ fn wait_internal<T: ?Sized, B: Backend>(
     /// [`CondVar::notify_one`] or [`CondVar::notify_all`]. Note that it may also wake up
     /// spuriously.
     pub fn wait<T: ?Sized, B: Backend>(&self, guard: &mut Guard<'_, T, B>) {
-        self.wait_internal(TASK_UNINTERRUPTIBLE, guard, MAX_SCHEDULE_TIMEOUT);
+        self.wait_internal(TASK_UNINTERRUPTIBLE, guard, Jiffies::MAX);
     }
 
     /// Releases the lock and waits for a notification in interruptible mode.
@@ -130,7 +129,7 @@ pub fn wait<T: ?Sized, B: Backend>(&self, guard: &mut Guard<'_, T, B>) {
     /// Returns whether there is a signal pending.
     #[must_use = "wait_interruptible returns if a signal is pending, so the caller must check the return value"]
     pub fn wait_interruptible<T: ?Sized, B: Backend>(&self, guard: &mut Guard<'_, T, B>) -> bool {
-        self.wait_internal(TASK_INTERRUPTIBLE, guard, MAX_SCHEDULE_TIMEOUT);
+        self.wait_internal(TASK_INTERRUPTIBLE, guard, Jiffies::MAX);
         crate::current!().signal_pending()
     }
 
@@ -145,11 +144,7 @@ pub fn wait_interruptible_freezable<T: ?Sized, B: Backend>(
         &self,
         guard: &mut Guard<'_, T, B>,
     ) -> bool {
-        self.wait_internal(
-            TASK_INTERRUPTIBLE | TASK_FREEZABLE,
-            guard,
-            MAX_SCHEDULE_TIMEOUT,
-        );
+        self.wait_internal(TASK_INTERRUPTIBLE | TASK_FREEZABLE, guard, Jiffies::MAX);
         crate::current!().signal_pending()
     }
 
@@ -164,10 +159,9 @@ pub fn wait_interruptible_timeout<T: ?Sized, B: Backend>(
         guard: &mut Guard<'_, T, B>,
         jiffies: Jiffies,
     ) -> CondVarTimeoutResult {
-        let jiffies = jiffies.try_into().unwrap_or(MAX_SCHEDULE_TIMEOUT);
-        let res = self.wait_internal(TASK_INTERRUPTIBLE, guard, jiffies);
+        let remaining = self.wait_internal(TASK_INTERRUPTIBLE, guard, jiffies);
 
-        match (res as Jiffies, crate::current!().signal_pending()) {
+        match (remaining, current!().signal_pending()) {
             (jiffies, true) => CondVarTimeoutResult::Signal { jiffies },
             (0, false) => CondVarTimeoutResult::Timeout,
             (jiffies, false) => CondVarTimeoutResult::Woken { jiffies },
-- 
2.56.0

[PATCH v2 5/5] rust: sync: condvar: add non-exclusive freezable waiting

[Danilo Krummrich]

CondVar currently registers all sleeping tasks as exclusive waiters.
Add wait_interruptible_freezable_nonexclusive() for callers that need
non-exclusive waits, using WaitQueue::wait_once().

Document that notify_one() and notify_sync() also wake all non-exclusive
waiters.

This provides non-exclusive waiting support for a subsequent Binder
conversion.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/sync/condvar.rs | 27 +++++++++++++++++++++++++--
 rust/kernel/sync/wait.rs    |  1 -
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/sync/condvar.rs b/rust/kernel/sync/condvar.rs
index fcab90f6ce34..cbc543de214f 100644
--- a/rust/kernel/sync/condvar.rs
+++ b/rust/kernel/sync/condvar.rs
@@ -148,6 +148,29 @@ pub fn wait_interruptible_freezable<T: ?Sized, B: Backend>(
         crate::current!().signal_pending()
     }
 
+    /// Releases the lock and waits non-exclusively in interruptible and freezable mode.
+    ///
+    /// Like [`CondVar::wait_interruptible_freezable`], but registers the current task as a
+    /// non-exclusive waiter.
+    ///
+    /// The lock is reacquired before returning. The wait may also end due to a signal or a
+    /// spurious wakeup.
+    ///
+    /// No lock other than the one released through `guard` should be held, since the task may
+    /// be frozen while sleeping.
+    ///
+    /// Returns whether there is a signal pending.
+    #[must_use = "the caller must check whether a signal is pending"]
+    pub fn wait_interruptible_freezable_nonexclusive<T: ?Sized, B: Backend>(
+        &self,
+        guard: &mut Guard<'_, T, B>,
+    ) -> bool {
+        self.wq.wait_once(TASK_INTERRUPTIBLE | TASK_FREEZABLE, || {
+            guard.do_unlocked(|| task::schedule_timeout(Jiffies::MAX))
+        });
+        crate::current!().signal_pending()
+    }
+
     /// Releases the lock and waits for a notification in interruptible mode.
     ///
     /// Atomically releases the given lock (whose ownership is proven by the guard) and puts the
@@ -168,7 +191,7 @@ pub fn wait_interruptible_timeout<T: ?Sized, B: Backend>(
         }
     }
 
-    /// Calls the kernel function to notify one thread synchronously.
+    /// Wakes all non-exclusive waiters and one exclusive waiter synchronously.
     ///
     /// This method behaves like `notify_one`, except that it hints to the scheduler that the
     /// current thread expects to sleep soon.
@@ -177,7 +200,7 @@ pub fn notify_sync(&self) {
         self.wq.wake_up_sync();
     }
 
-    /// Wakes a single waiter up, if any.
+    /// Wakes all non-exclusive waiters and one exclusive waiter, if any.
     ///
     /// This is not 'sticky' in the sense that if no thread is waiting, the notification is lost
     /// completely (as opposed to automatically waking up the next waiter).
diff --git a/rust/kernel/sync/wait.rs b/rust/kernel/sync/wait.rs
index 92c1ae93705e..942f96b5cf17 100644
--- a/rust/kernel/sync/wait.rs
+++ b/rust/kernel/sync/wait.rs
@@ -208,7 +208,6 @@ fn wait_event_timeout_internal<F: FnMut() -> bool>(
     /// Performs a single non-exclusive prepare-to-wait / finish-wait cycle, calling `schedule_fn`
     /// in between. Non-exclusive waiters are all woken by [`wake_up()`](Self::wake_up).
     #[inline]
-    #[expect(unused)]
     pub(super) fn wait_once<F, R>(&self, wait_state: c_int, schedule_fn: F) -> R
     where
         F: FnOnce() -> R,
-- 
2.56.0