rust: sync: add `CondVar::wait_timeout`

Sleep on a condition variable with a timeout.

This is used by Rust Binder for process freezing. There, we want to
sleep until the freeze operation completes, but we want to be able to
abort the process freezing if it doesn't complete within some timeout.

Note that it is not enough to avoid jiffies by introducing a variant of
`CondVar::wait_timeout` that takes the timeout in msecs because we need
to be able to restart the sleep with the remaining sleep duration if it
is interrupted, and if the API takes msecs rather than jiffies, then
that would require a conversion roundtrip jiffies->msecs->jiffies that
is best avoided.

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Tiago Lam <tiagolam@gmail.com>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20240108-rb-new-condvar-methods-v4-3-88e0c871cc05@google.com
[ Added `CondVarTimeoutResult` re-export and fixed typo. ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
index d219ee518eff155066cf4c7422ccb9614925dedb..c1fb10fc64f4b61f64b4b34fe72bc44fd7fd170a 100644 (file)
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -13,7 +13,7 @@ pub mod lock;
 mod locked_by;
 
 pub use arc::{Arc, ArcBorrow, UniqueArc};
-pub use condvar::CondVar;
+pub use condvar::{CondVar, CondVarTimeoutResult};
 pub use lock::{mutex::Mutex, spinlock::SpinLock};
 pub use locked_by::LockedBy;
 

diff --git a/rust/kernel/sync/condvar.rs b/rust/kernel/sync/condvar.rs
index 30fb5cbfb730f4a2aa420db4be10ea82d2956841..3f148d7040bb9abebaa0b923a02285bb0bf9ca06 100644 (file)
--- a/rust/kernel/sync/condvar.rs
+++ b/rust/kernel/sync/condvar.rs
@@ -6,7 +6,11 @@
 //! variable.
 
 use super::{lock::Backend, lock::Guard, LockClassKey};
-use crate::{bindings, init::PinInit, pin_init, str::CStr, types::Opaque};
+use crate::{
+    bindings, init::PinInit, pin_init, str::CStr, task::MAX_SCHEDULE_TIMEOUT, time::Jiffies,
+    types::Opaque,
+};
+use core::ffi::c_long;
 use core::marker::PhantomPinned;
 use macros::pin_data;
 
@@ -102,7 +106,12 @@ impl CondVar {
         })
     }
 
-    fn wait_internal<T: ?Sized, B: Backend>(&self, wait_state: u32, guard: &mut Guard<'_, T, B>) {
+    fn wait_internal<T: ?Sized, B: Backend>(
+        &self,
+        wait_state: u32,
+        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.
@@ -117,11 +126,13 @@ impl CondVar {
             )
         };
 
-        // SAFETY: No arguments, switches to another thread.
-        guard.do_unlocked(|| unsafe { bindings::schedule() });
+        // 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.
@@ -131,7 +142,7 @@ impl CondVar {
     /// [`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(bindings::TASK_UNINTERRUPTIBLE, guard);
+        self.wait_internal(bindings::TASK_UNINTERRUPTIBLE, guard, MAX_SCHEDULE_TIMEOUT);
     }
 
     /// Releases the lock and waits for a notification in interruptible mode.
@@ -142,10 +153,31 @@ impl CondVar {
     /// 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(bindings::TASK_INTERRUPTIBLE, guard);
+        self.wait_internal(bindings::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(bindings::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 with the given flags.
     fn notify(&self, count: i32, flags: u32) {
         // SAFETY: `wait_queue_head` points to valid memory.
@@ -185,3 +217,19 @@ impl CondVar {
         self.notify(0, 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,
+    },
+}

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index f12a684bc9579458c0cd016c06668f03e6b7fb5f..149a5259d431a8bafa1a127e59f2a7cc823a1ef8 100644 (file)
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -139,7 +139,7 @@ pub struct Guard<'a, T: ?Sized, B: Backend> {
 unsafe impl<T: Sync + ?Sized, B: Backend> Sync for Guard<'_, T, B> {}
 
 impl<T: ?Sized, B: Backend> Guard<'_, T, B> {
-    pub(crate) fn do_unlocked(&mut self, cb: impl FnOnce()) {
+    pub(crate) fn do_unlocked<U>(&mut self, cb: impl FnOnce() -> U) -> U {
         // SAFETY: The caller owns the lock, so it is safe to unlock it.
         unsafe { B::unlock(self.lock.state.get(), &self.state) };
 
@@ -147,7 +147,7 @@ impl<T: ?Sized, B: Backend> Guard<'_, T, B> {
         let _relock =
             ScopeGuard::new(|| unsafe { B::relock(self.lock.state.get(), &mut self.state) });
 
-        cb();
+        cb()
     }
 }
 

diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
index 9451932d5d867419eb3bad9d01bea40a96e10ea1..49a8e10d68f5a0ed076dcb0aa0213551996a19e4 100644 (file)
--- a/rust/kernel/task.rs
+++ b/rust/kernel/task.rs
@@ -5,7 +5,10 @@
 //! C header: [`include/linux/sched.h`](srctree/include/linux/sched.h).
 
 use crate::{bindings, types::Opaque};
-use core::{marker::PhantomData, ops::Deref, ptr};
+use core::{ffi::c_long, marker::PhantomData, ops::Deref, ptr};
+
+/// A sentinel value used for infinite timeouts.
+pub const MAX_SCHEDULE_TIMEOUT: c_long = c_long::MAX;
 
 /// Returns the currently running task.
 #[macro_export]