// SPDX-License-Identifier: GPL-2.0
//! A condition variable.
//!
//! 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 crate::{
init::PinInit,
pin_init,
str::CStr,
task::{MAX_SCHEDULE_TIMEOUT, TASK_INTERRUPTIBLE, TASK_NORMAL, TASK_UNINTERRUPTIBLE},
time::Jiffies,
types::Opaque,
};
use core::ffi::{c_int, c_long};
use core::marker::PhantomPinned;
use core::ptr;
use macros::pin_data;
/// Creates a [`CondVar`] initialiser with the given name and a newly-created lock class.
#[macro_export]
macro_rules! new_condvar {
($($name:literal)?) => {
$crate::sync::CondVar::new($crate::optional_name!($($name)?), $crate::static_lock_class!())
};
}
pub use new_condvar;
/// A conditional variable.
///
/// Exposes the kernel's [`struct wait_queue_head`] as a condition variable. It allows the caller to
/// atomically release the given lock and go to sleep. It reacquires the lock when it wakes up. And
/// it wakes up when notified by another thread (via [`CondVar::notify_one`] or
/// [`CondVar::notify_all`]) or because the thread received a signal. It may also wake up
/// spuriously.
///
/// Instances of [`CondVar`] need a lock class and to be pinned. The recommended way to create such
/// instances is with the [`pin_init`](crate::pin_init) and [`new_condvar`] macros.
///
/// # Examples
///
/// The following is an example of using a condvar with a mutex:
///
/// ```
/// use kernel::sync::{new_condvar, new_mutex, CondVar, Mutex};
///
/// #[pin_data]
/// pub struct Example {
/// #[pin]
/// value: Mutex<u32>,
///
/// #[pin]
/// value_changed: CondVar,
/// }
///
/// /// Waits for `e.value` to become `v`.
/// fn wait_for_value(e: &Example, v: u32) {
/// let mut guard = e.value.lock();
/// while *guard != v {
/// e.value_changed.wait(&mut guard);
/// }
/// }
///
/// /// Increments `e.value` and notifies all potential waiters.
/// fn increment(e: &Example) {
/// *e.value.lock() += 1;
/// e.value_changed.notify_all();
/// }
///
/// /// Allocates a new boxed `Example`.
/// fn new_example() -> Result<Pin<Box<Example>>> {
/// Box::pin_init(pin_init!(Example {
/// value <- new_mutex!(0),
/// value_changed <- new_condvar!(),
/// }), GFP_KERNEL)
/// }
/// ```
///
/// [`struct wait_queue_head`]: srctree/include/linux/wait.h
#[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,
}
// SAFETY: `CondVar` only uses a `struct wait_queue_head`, which is safe to use on any thread.
#[allow(clippy::non_send_fields_in_send_ty)]
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: &'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())
}),
})
}
fn wait_internal<T: ?Sized, B: Backend>(
&self,
wait_state: c_int,
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
}
/// Releases the lock and waits for a notification in uninterruptible mode.
///
/// Atomically releases the given lock (whose ownership is proven by the guard) and puts the
/// thread to sleep, reacquiring the lock on wake up. It wakes up when notified by
/// [`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);
}
/// Releases the lock and waits for a notification in interruptible mode.
///
/// Similar to [`CondVar::wait`], except that the wait is interruptible. That is, the thread may
/// wake up due to signals. It may also wake up spuriously.
///
/// 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);
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
/// thread to sleep. It wakes up when notified by [`CondVar::notify_one`] or
/// [`CondVar::notify_all`], or when a timeout occurs, or when the thread receives a signal.
#[must_use = "wait_interruptible_timeout returns if a signal is pending, so the caller must check the return value"]
pub fn wait_interruptible_timeout<T: ?Sized, B: Backend>(
&self,
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);
match (res as Jiffies, crate::current!().signal_pending()) {
(jiffies, true) => CondVarTimeoutResult::Signal { jiffies },
(0, false) => CondVarTimeoutResult::Timeout,
(jiffies, false) => CondVarTimeoutResult::Woken { jiffies },
}
}
/// 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.
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) };
}
/// Wakes a single waiter up, 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).
pub fn notify_one(&self) {
self.notify(1);
}
/// Wakes all waiters up, 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).
pub fn notify_all(&self) {
self.notify(0);
}
}
/// The return type of `wait_timeout`.
pub enum CondVarTimeoutResult {
/// The timeout was reached.
Timeout,
/// Somebody woke us up.
Woken {
/// Remaining sleep duration.
jiffies: Jiffies,
},
/// A signal occurred.
Signal {
/// Remaining sleep duration.
jiffies: Jiffies,
},
}
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