rust: add ww_mutex support

index 440fb7638e3c..0287064c82c1 100644
@@ -105,4 +105,5 @@
 #include "vmalloc.c"
 #include "wait.c"
 #include "workqueue.c"
+#include "ww_mutex.c"
 #include "xarray.c"

new file mode 100644
index 000000000000..e7aa65ac5874
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/ww_mutex.h>
+
+__rust_helper
+void rust_helper_ww_mutex_init(struct ww_mutex *lock, struct ww_class *ww_class)
+{
+	ww_mutex_init(lock, ww_class);
+}
+
+__rust_helper
+void rust_helper_ww_acquire_init(struct ww_acquire_ctx *ctx, struct ww_class *ww_class)
+{
+	ww_acquire_init(ctx, ww_class);
+}
+
+__rust_helper
+void rust_helper_ww_acquire_done(struct ww_acquire_ctx *ctx)
+{
+	ww_acquire_done(ctx);
+}
+
+__rust_helper
+void rust_helper_ww_acquire_fini(struct ww_acquire_ctx *ctx)
+{
+	ww_acquire_fini(ctx);
+}
+
+__rust_helper
+bool rust_helper_ww_mutex_is_locked(struct ww_mutex *lock)
+{
+	return ww_mutex_is_locked(lock);
+}

index 0c95ead5a297..c955824aa5d4 100644
@@ -48,9 +48,7 @@ struct ww_class {
 context_lock_struct(ww_mutex) {
 	struct WW_MUTEX_BASE base;
 	struct ww_acquire_ctx *ctx;
-#ifdef DEBUG_WW_MUTEXES
 	struct ww_class *ww_class;
-#endif
 };
 
 context_lock_struct(ww_acquire_ctx) {

@@ -59,9 +57,9 @@ context_lock_struct(ww_acquire_ctx) {
 	unsigned int acquired;
 	unsigned short wounded;
 	unsigned short is_wait_die;
+	struct ww_class *ww_class;
 #ifdef DEBUG_WW_MUTEXES
 	unsigned int done_acquire;
-	struct ww_class *ww_class;
 	void *contending_lock;
 #endif
 #ifdef CONFIG_DEBUG_LOCK_ALLOC

@@ -111,9 +109,7 @@ static inline void ww_mutex_init(struct ww_mutex *lock,
 {
 	ww_mutex_base_init(&lock->base, ww_class->mutex_name, &ww_class->mutex_key);
 	lock->ctx = NULL;
-#ifdef DEBUG_WW_MUTEXES
 	lock->ww_class = ww_class;
-#endif
 }
 
 /**

@@ -149,8 +145,8 @@ static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
 	ctx->acquired = 0;
 	ctx->wounded = false;
 	ctx->is_wait_die = ww_class->is_wait_die;
-#ifdef DEBUG_WW_MUTEXES
 	ctx->ww_class = ww_class;
+#ifdef DEBUG_WW_MUTEXES
 	ctx->done_acquire = 0;
 	ctx->contending_lock = NULL;
 #endif

index 10b6b5e9b024..f509250822c5 100644
@@ -15,6 +15,7 @@
 
 pub mod mutex;
 pub mod spinlock;
+pub mod ww_mutex;
 
 pub(super) mod global;
 pub use global::{GlobalGuard, GlobalLock, GlobalLockBackend, GlobalLockedBy};

new file mode 100644
index 000000000000..727c51cc73af
@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust abstractions for the kernel's wound-wait locking primitives.
+
+pub use class::Class;
+
+mod class;

144 lines not on this page · raw message

index 727c51cc73af..1626ec811a83 100644
@@ -1,7 +1,437 @@
 // SPDX-License-Identifier: GPL-2.0
 
 //! Rust abstractions for the kernel's wound-wait locking primitives.
+//!
+//! It is designed to avoid deadlocks when locking multiple [`Mutex`]es
+//! that belong to the same [`Class`]. Each lock acquisition uses an
+//! [`AcquireCtx`] to track ordering and ensure forward progress.
+//!
+//! See srctree/Documentation/locking/ww-mutex-design.rst for more details.
 
+use crate::{
+    bindings,
+    container_of,
+    error::to_result,
+    prelude::*,
+    types::{
+        NotThreadSafe,
+        Opaque, //
+    }, //
+};
+use core::{
+    cell::UnsafeCell,
+    marker::PhantomData, //
+};
+
+pub use acquire_ctx::AcquireCtx;
 pub use class::Class;
 
+mod acquire_ctx;
 mod class;
+
+/// A wound-wait (ww) mutex that is powered with deadlock avoidance
+/// when acquiring multiple locks of the same [`Class`].
+///
+/// Each mutex belongs to a [`Class`], which the wound-wait algorithm
+/// uses to figure out the order of acquisition and prevent deadlocks.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::{
+///     define_ww_class,
+///     sync::{
+///         lock::ww_mutex::{
+///             AcquireCtx,
+///             Class,
+///             Mutex, //
+///         },
+///         Arc,
+///     },
+/// };
+/// use pin_init::stack_pin_init;
+///
+/// define_ww_class!(SOME_WW_CLASS);
+///
+/// let mutex = Arc::pin_init(Mutex::new(42, &SOME_WW_CLASS), GFP_KERNEL)?;
+/// let ctx = KBox::pin_init(AcquireCtx::new(&SOME_WW_CLASS), GFP_KERNEL)?;
+///
+/// // SAFETY: The guard is dropped before `ctx`.
+/// let guard = unsafe { ctx.lock(&mutex) }?;
+/// assert_eq!(*guard, 42);
+///
+/// # Ok::<(), Error>(())
+/// ```
+#[pin_data]
+#[repr(C)]
+pub struct Mutex<'a, T: ?Sized> {
+    _p: PhantomData<&'a Class>,
+    #[pin]
+    inner: Opaque<bindings::ww_mutex>,
+    data: UnsafeCell<T>,
+}
+
+impl<'class, T> Mutex<'class, T> {
+    /// Initializes [`Mutex`] with the given `data` and [`Class`].
+    pub fn new(data: T, class: &'class Class) -> impl PinInit<Self> {
+        let class_ptr = class.inner.get();
+        pin_init!(Mutex {
+            inner <- Opaque::ffi_init(|slot: *mut bindings::ww_mutex| {
+                // SAFETY: `class` is valid for the lifetime `'class` captured by `Self`.
+                unsafe { bindings::ww_mutex_init(slot, class_ptr) }
+            }),
+            data: UnsafeCell::new(data),
+            _p: PhantomData
+        })
+    }
+}
+
+impl<'class, T: ?Sized> Mutex<'class, T> {
+    /// Checks if this [`Mutex`] is currently locked.
+    ///
+    /// The returned value is racy as another thread can acquire
+    /// or release the lock immediately after this call returns.
+    pub fn is_locked(&self) -> bool {
+        // SAFETY: It's safe to call `ww_mutex_is_locked` on
+        // a valid mutex.
+        unsafe { bindings::ww_mutex_is_locked(self.inner.get()) }
+    }
+
+    /// Locks this [`Mutex`] without [`AcquireCtx`].
+    pub fn lock(&self) -> Result<MutexGuard<'_, T>> {
+        lock_common(self, None, LockKind::Regular)
+    }
+
+    /// Similar to [`Self::lock`], but can be interrupted by signals.
+    pub fn lock_interruptible(&self) -> Result<MutexGuard<'_, T>> {
+        lock_common(self, None, LockKind::Interruptible)
+    }
+
+    /// Tries to lock this [`Mutex`] with no [`AcquireCtx`] and without blocking.
+    ///
+    /// Unlike [`Self::lock`], no deadlock handling is performed.
+    pub fn try_lock(&self) -> Result<MutexGuard<'_, T>> {
+        lock_common(self, None, LockKind::Try)
+    }
+}
+
+impl<'class> Mutex<'class, ()> {
+    /// Creates a [`Mutex`] from a raw pointer.
+    ///
+    /// This function is intended for interoperability with C code.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that:
+    ///
+    /// - `ptr` is a valid pointer to a `ww_mutex`.
+    /// - `ptr` must remain valid for the lifetime `'a`.
+    /// - ww_class associated with this mutex must be valid for
+    ///   the lifetime `'class`.
+    pub unsafe fn from_raw<'a>(ptr: *mut bindings::ww_mutex) -> &'a Self {
+        // SAFETY: By the safety contract, the caller guarantees that `ptr`
+        // points to a valid `ww_mutex` which is the `inner` field of `Mutex`,
+        // that it remains valid for the lifetime `'a` and the associated
+        // ww_class outlives `'class`.
+        //
+        // Because [`Mutex`] is `#[repr(C)]`, the `inner` field sits at a
+        // stable offset that `container_of!` can safely rely on.
+        unsafe { &*container_of!(Opaque::cast_from(ptr), Self, inner) }
+    }
+}
+
+// SAFETY: `Mutex` can be sent to another thread if the protected
+// data `T` can be.
+unsafe impl<T: ?Sized + Send> Send for Mutex<'_, T> {}
+
+// SAFETY: `Mutex` serialises access to the protected data, so it is
+// `Sync` as long as the data is `Send`.
+unsafe impl<T: ?Sized + Send> Sync for Mutex<'_, T> {}
+
+/// A guard that provides exclusive access to the data protected
+/// by a [`Mutex`].
+///
+/// # Invariants
+///
+/// The guard holds an exclusive lock on the associated [`Mutex`]. The lock is held
+/// for the entire lifetime of this guard and is automatically released when the
+/// guard is dropped.
+#[must_use = "the lock unlocks immediately when the guard is unused"]
+pub struct MutexGuard<'a, T: ?Sized> {
+    mutex: &'a Mutex<'a, T>,
+    _not_send: NotThreadSafe,
+}
+
+impl<'a, T: ?Sized> MutexGuard<'a, T> {
+    /// Creates a new guard for the given [`Mutex`].
+    fn new(mutex: &'a Mutex<'a, T>) -> Self {
+        assert!(mutex.is_locked());
+
+        Self {
+            mutex,
+            _not_send: NotThreadSafe,
+        }
+    }
+}
+
+impl<'a> MutexGuard<'a, ()> {
+    /// Creates a [`MutexGuard`] from a raw pointer.
+    ///
+    /// If the given pointer refers to a mutex that is not locked,
+    /// returns [`EINVAL`].
+    ///
+    /// This function is intended for interoperability with C code.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that:
+    ///
+    /// - `ptr` is a valid pointer to a `ww_mutex`.
+    /// - `ptr` must remain valid for the lifetime `'b`.
+    /// - The `ww_class` associated with the `ww_mutex` must be valid for the lifetime `'b`.
+    /// - The current task holds the mutex.
+    /// - The caller transfers responsibility for unlocking the mutex to the returned guard
+    ///   and must not unlock it separately (including through another guard).
+    /// - Any associated acquire context remains valid until the mutex is unlocked,
+    ///   even if the returned guard is forgotten. The context must not be finalized or
+    ///   reinitialized before then.
+    pub unsafe fn from_raw<'b>(ptr: *mut bindings::ww_mutex) -> Result<MutexGuard<'b, ()>> {
+        // SAFETY: By this function's safety contract, the caller guarantees that `ptr` points to a
+        // valid `ww_mutex` which is the `inner` field of a `Mutex`. The caller also guarantees
+        // that both `ptr` and the associated `ww_class` are valid for the lifetime `'b`.
+        let mutex = unsafe { Mutex::from_raw(ptr) };
+
+        if !mutex.is_locked() {
+            return Err(EINVAL);
+        }
+
+        Ok(MutexGuard::new(mutex))
+    }
+}
+
+impl<T: ?Sized> core::ops::Deref for MutexGuard<'_, T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        // SAFETY: self.mutex is locked, so we have exclusive access.
+        unsafe { &*self.mutex.data.get() }
+    }
+}
+
+impl<T: ?Sized + Unpin> core::ops::DerefMut for MutexGuard<'_, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        // SAFETY: self.mutex is locked, so we have exclusive access.
+        unsafe { &mut *self.mutex.data.get() }
+    }
+}
+
+impl<T: ?Sized> Drop for MutexGuard<'_, T> {
+    fn drop(&mut self) {
+        // SAFETY: self.mutex is locked and are about to release it.
+        unsafe { bindings::ww_mutex_unlock(self.mutex.inner.get()) };
+    }
+}
+
+// SAFETY: `MutexGuard` can be shared between threads if the data can.
+unsafe impl<T: ?Sized + Sync> Sync for MutexGuard<'_, T> {}
+
+/// Locking kinds used by [`lock_common`] to unify the internal
+/// locking logic.
+///
+/// It's best not to expose this type (and [`lock_common`]) to the
+/// kernel, as it allows internal API changes without worrying
+/// about breaking external compatibility.
+#[derive(Copy, Clone, Debug)]
+enum LockKind {
+    /// Blocks until lock is acquired.
+    Regular,
+    /// Blocks but can be interrupted by signals.
+    Interruptible,
+    /// Does not block, returns immediately if busy.
+    Try,
+}
+
+/// Internal helper that unifies the different locking kinds.
+///
+/// Returns [`EINVAL`] if the [`Mutex`] has a different [`Class`].
+fn lock_common<'a, T: ?Sized>(
+    mutex: &'a Mutex<'a, T>,
+    ctx: Option<&AcquireCtx<'_>>,
+    kind: LockKind,
+) -> Result<MutexGuard<'a, T>> {
+    let mutex_ptr = mutex.inner.get();
+
+    let ctx_ptr = match ctx {
+        Some(acquire_ctx) => {
+            let ctx_ptr = acquire_ctx.inner.get();
+
+            // SAFETY: `ctx_ptr` is a valid pointer for the entire
+            // lifetime of `ctx`.
+            let ctx_class = unsafe { (*ctx_ptr).ww_class };
+
+            // SAFETY: `mutex_ptr` is a valid pointer for the entire
+            // lifetime of `mutex`.
+            let mutex_class = unsafe { (*mutex_ptr).ww_class };
+
+            // `ctx` and `mutex` must use the same class.
+            if ctx_class != mutex_class {
+                return Err(EINVAL);
+            }
+
+            ctx_ptr
+        }
+        None => core::ptr::null_mut(),
+    };
+
+    match kind {
+        LockKind::Regular => {
+            // SAFETY: `Mutex` is always pinned. If `AcquireCtx` is `Some`, it is pinned,
+            // if `None`, it is set to `core::ptr::null_mut()`. Both cases are safe.
+            let ret = unsafe { bindings::ww_mutex_lock(mutex_ptr, ctx_ptr) };
+
+            to_result(ret)?;
+        }
+        LockKind::Interruptible => {
+            // SAFETY: `Mutex` is always pinned. If `AcquireCtx` is `Some`, it is pinned,
+            // if `None`, it is set to `core::ptr::null_mut()`. Both cases are safe.
+            let ret = unsafe { bindings::ww_mutex_lock_interruptible(mutex_ptr, ctx_ptr) };
+
+            to_result(ret)?;
+        }
+        LockKind::Try => {
+            // SAFETY: `Mutex` is always pinned. If `AcquireCtx` is `Some`, it is pinned,
+            // if `None`, it is set to `core::ptr::null_mut()`. Both cases are safe.
+            let ret = unsafe { bindings::ww_mutex_trylock(mutex_ptr, ctx_ptr) };
+
+            if ret == 0 {
+                return Err(EBUSY);
+            } else {
+                to_result(ret)?;
+            }
+        }
+    };
+
+    Ok(MutexGuard::new(mutex))
+}
+
+#[kunit_tests(rust_kernel_ww_mutex)]
+mod tests {
+    use super::*;
+    use crate::{
+        define_wd_class,
+        define_ww_class,
+        sync::Arc, //
+    };
+
+    define_ww_class!(TEST_WOUND_WAIT_CLASS);
+    define_wd_class!(TEST_WAIT_DIE_CLASS);
+
+    #[test]
+    fn test_ww_mutex_basic_lock_unlock() -> Result {
+        let mutex = Arc::pin_init(Mutex::new(42, &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+        let ctx = KBox::pin_init(AcquireCtx::new(&TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+
+        // SAFETY: The guard is dropped before `ctx`.
+        let guard = unsafe { ctx.lock(&mutex) }?;
+        assert_eq!(*guard, 42);
+
+        // Drop the lock.
+        drop(guard);
+
+        // SAFETY: The guard is dropped before `ctx`.
+        let mut guard = unsafe { ctx.lock(&mutex) }?;
+        *guard = 100;
+        assert_eq!(*guard, 100);
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_ww_mutex_trylock() -> Result {
+        let mutex = Arc::pin_init(Mutex::new(123, &TEST_WAIT_DIE_CLASS), GFP_KERNEL)?;
+        let ctx = KBox::pin_init(AcquireCtx::new(&TEST_WAIT_DIE_CLASS), GFP_KERNEL)?;
+
+        // `try_lock` on unlocked mutex should succeed.
+        // SAFETY: The guard is dropped before `ctx`.
+        let guard = unsafe { ctx.try_lock(&mutex) }?;
+        assert_eq!(*guard, 123);
+
+        // Now it should fail immediately as it's already locked.
+        // SAFETY: Any returned guard is dropped immediately, before `ctx`.
+        assert!(unsafe { ctx.try_lock(&mutex) }.is_err());
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_ww_mutex_is_locked() -> Result {
+        let mutex = Arc::pin_init(Mutex::new("hello", &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+        let ctx = KBox::pin_init(AcquireCtx::new(&TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+
+        // Should not be locked initially.
+        assert!(!mutex.is_locked());
+
+        // SAFETY: The guard is dropped before `ctx`.
+        let guard = unsafe { ctx.lock(&mutex) }?;
+        assert!(mutex.is_locked());
+
+        drop(guard);
+        assert!(!mutex.is_locked());
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_ww_acquire_context_done() -> Result {
+        let mutex1 = Arc::pin_init(Mutex::new(1, &TEST_WAIT_DIE_CLASS), GFP_KERNEL)?;
+        let mutex2 = Arc::pin_init(Mutex::new(2, &TEST_WAIT_DIE_CLASS), GFP_KERNEL)?;
+        let ctx = KBox::pin_init(AcquireCtx::new(&TEST_WAIT_DIE_CLASS), GFP_KERNEL)?;
+
+        // Acquire multiple mutexes with the same context.
+        // SAFETY: The guard is dropped before `ctx`.
+        let guard1 = unsafe { ctx.lock(&mutex1) }?;
+        // SAFETY: The guard is dropped before `ctx`.
+        let guard2 = unsafe { ctx.lock(&mutex2) }?;
+
+        assert_eq!(*guard1, 1);
+        assert_eq!(*guard2, 2);
+
+        ctx.done();
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_mutex_without_ctx() -> Result {
+        let mutex = Arc::pin_init(Mutex::new(100, &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+        let guard = mutex.lock()?;
+
+        assert_eq!(*guard, 100);
+        assert!(mutex.is_locked());
+
+        drop(guard);
+
+        assert!(!mutex.is_locked());
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_guard_from_raw_unlocks_mutex() -> Result {
+        let mutex = Arc::pin_init(Mutex::new((), &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+        let guard = mutex.lock()?;
+
+        // Keep the mutex locked without leaving another guard responsible for unlocking it.
+        core::mem::forget(guard);
+
+        // SAFETY: `mutex` and its class remain valid for this test. The current task holds
+        // the mutex, and forgetting the previous guard lets this guard take over unlocking it.
+        let guard = unsafe { MutexGuard::from_raw(mutex.inner.get()) }?;
+        assert!(mutex.is_locked());
+
+        drop(guard);
+        assert!(!mutex.is_locked());
+
+        Ok(())
+    }
+}

148 lines not on this page · raw message

index 1626ec811a83..99b5a32d033d 100644
@@ -6,6 +6,10 @@
 //! that belong to the same [`Class`]. Each lock acquisition uses an
 //! [`AcquireCtx`] to track ordering and ensure forward progress.
 //!
+//! It is recommended to use [`LockSet`] as it provides safe high-level
+//! interface that automatically handles deadlocks, retries and context
+//! management.
+//!
 //! See srctree/Documentation/locking/ww-mutex-design.rst for more details.
 
 use crate::{

@@ -25,9 +29,11 @@
 
 pub use acquire_ctx::AcquireCtx;
 pub use class::Class;
+pub use lock_set::LockSet;
 
 mod acquire_ctx;
 mod class;
+mod lock_set;
 
 /// A wound-wait (ww) mutex that is powered with deadlock avoidance
 /// when acquiring multiple locks of the same [`Class`].

448 lines not on this page · raw message