[PATCH v10 0/7] rust: add ww_mutex support

[PATCH v10 0/7] rust: add ww_mutex support

[Onur Özkan]

Changes in v10:
  - Added missing reviewed-by tags.
  - Fixed git conflict resolution leftovers [1].

[1]: https://lore.kernel.org/all/202601030632.SukxzGNs-lkp@intel.com/

Changes in v9:
  - Added `__rust_helper` prefixes to `ww_mutex.c`.
  - Reworked on Class to remove pinned initialization functions
    and added documentation suggesting its use as a global variable
    as this is its only usage on the C side.
  - Added myself as a maintainer of WW Mutex.
  - Various minor updates (commit description updates, minor code
    rearrangements, etc.).

Changes in v8:
  - Various minor updates (e.g., doc updates, removing unnecessary
    lifetime annotations, etc.).
  - Changed C implementation to always provide ww_class field in
    ww_mutex and ww_acquire_ctx types so we can access it from Rust
    easily.
  - Locking functions are now safe to call.
  - Added class validation logic to ww_mutex::lock_common.

Changes in v7:
  - Split Class and AcquireCtx into separate modules.
  - Removed "Ww" prefixes from type names.
  - Renamed exec.rs -> lock_set.rs and ExecContext -> LockSet.
  - Removed transmute logic from LockSet (formerly ExecContext).
  - Improved various doc-comments.
  - Marked certain AcquireCtx functions as unsafe.
  - Added from_raw constructors for Mutex, MutexGuard, AcquireCtx
    and Class.
  - LockSet::cleanup_on_deadlock no longer triggers reallocations when
    reinitializing AcquireCtx.
  - Incorporated various minor improvements suggested on the v6 series.

Changes in v6:
  - Added `unpinned_new` constructor for `WwClass` and updated
    global macros.
  - Changed all tests (and docs) to use Arc/KBox instead of
    `stack_pin_init` for `WwMutex` and `WwAcquireCtx`.
  - Added `LockKind` and `lock_common` helper to unify locking logic.
  - Added context-based and context-free locking functions for `WwMutex`.
  - Added `ww_mutex/exec` module, a high-level API with auto `EDEADLK`
    handling mechanism.

Changes in v5:
  - Addressed documentation review notes.
  - Removed `unwrap()`s in examples and KUnit tests.

Onur Özkan (7):
  rust: add C wrappers for ww_mutex inline functions
  ww_mutex: add ww_class field unconditionally
  rust: error: add EDEADLK
  rust: implement Class for ww_class support
  rust: ww_mutex: add Mutex, AcquireCtx and MutexGuard
  rust: ww_mutex: implement LockSet
  MAINTAINERS: add Onur Özkan as WW MUTEX maintainer

 MAINTAINERS                                   |   2 +
 include/linux/ww_mutex.h                      |   8 +-
 rust/helpers/helpers.c                        |   1 +
 rust/helpers/ww_mutex.c                       |  45 ++
 rust/kernel/error.rs                          |   1 +
 rust/kernel/sync/lock.rs                      |   1 +
 rust/kernel/sync/lock/ww_mutex.rs             | 444 ++++++++++++++++++
 rust/kernel/sync/lock/ww_mutex/acquire_ctx.rs | 172 +++++++
 rust/kernel/sync/lock/ww_mutex/class.rs       | 139 ++++++
 rust/kernel/sync/lock/ww_mutex/lock_set.rs    | 370 +++++++++++++++
 10 files changed, 1177 insertions(+), 6 deletions(-)
 create mode 100644 rust/helpers/ww_mutex.c
 create mode 100644 rust/kernel/sync/lock/ww_mutex.rs
 create mode 100644 rust/kernel/sync/lock/ww_mutex/acquire_ctx.rs
 create mode 100644 rust/kernel/sync/lock/ww_mutex/class.rs
 create mode 100644 rust/kernel/sync/lock/ww_mutex/lock_set.rs

-- 
2.51.2

[PATCH v10 1/7] rust: add C wrappers for ww_mutex inline functions

[Onur Özkan]

Some of the kernel's `ww_mutex` functions are implemented as
`static inline`, so they are inaccessible from Rust as bindgen
can't generate code on them. This patch provides C function wrappers
around these inline implementations, so bindgen can see them and
generate the corresponding Rust code.

Signed-off-by: Onur Özkan <work@onurozkan.dev>
---
 MAINTAINERS             |  1 +
 rust/helpers/helpers.c  |  1 +
 rust/helpers/ww_mutex.c | 45 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 47 insertions(+)
 create mode 100644 rust/helpers/ww_mutex.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 765ad2daa218..d245b7b38b21 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -14728,6 +14728,7 @@ F:	kernel/locking/
 F:	lib/locking*.[ch]
 F:	rust/helpers/mutex.c
 F:	rust/helpers/spinlock.c
+F:	rust/helpers/ww_mutex.c
 F:	rust/kernel/sync/lock.rs
 F:	rust/kernel/sync/lock/
 F:	rust/kernel/sync/locked_by.rs
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 79c72762ad9c..a95fb3abaab3 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -61,4 +61,5 @@
 #include "vmalloc.c"
 #include "wait.c"
 #include "workqueue.c"
+#include "ww_mutex.c"
 #include "xarray.c"
diff --git a/rust/helpers/ww_mutex.c b/rust/helpers/ww_mutex.c
new file mode 100644
index 000000000000..2ea19aafbd4e
--- /dev/null
+++ b/rust/helpers/ww_mutex.c
@@ -0,0 +1,45 @@
+// 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
+void rust_helper_ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
+{
+	ww_mutex_lock_slow(lock, ctx);
+}
+
+__rust_helper
+int rust_helper_ww_mutex_lock_slow_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
+{
+	return ww_mutex_lock_slow_interruptible(lock, ctx);
+}
+
+__rust_helper
+bool rust_helper_ww_mutex_is_locked(struct ww_mutex *lock)
+{
+	return ww_mutex_is_locked(lock);
+}
-- 
2.51.2

[PATCH v10 2/7] ww_mutex: add ww_class field unconditionally

[Onur Özkan]

Removes DEBUG_WW_MUTEXES guard around the ww_class field
in struct ww_mutex and struct ww_acquire_ctx to always
initialize it.

Keeping the class pointer available unconditionally allows
Rust abstractions to keep from_raw() simple on Mutex and
AcquireCtx, simplify AcquireCtx reinitialization logic and
validate Mutex and AcquireCtx class pairing in much simpler way.

Link: https://lore.kernel.org/all/ECC0425A-8B18-4626-8EA8-2F843C45E0A1@collabora.com/
Signed-off-by: Onur Özkan <work@onurozkan.dev>
---
 include/linux/ww_mutex.h | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
index 45ff6f7a872b..c9835035b6d6 100644
--- a/include/linux/ww_mutex.h
+++ b/include/linux/ww_mutex.h
@@ -47,9 +47,7 @@ struct ww_class {
 struct ww_mutex {
 	struct WW_MUTEX_BASE base;
 	struct ww_acquire_ctx *ctx;
-#ifdef DEBUG_WW_MUTEXES
 	struct ww_class *ww_class;
-#endif
 };
 
 struct ww_acquire_ctx {
@@ -58,9 +56,9 @@ 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
@@ -110,9 +108,7 @@ 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
 }
 
 /**
@@ -147,8 +143,8 @@ 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
-- 
2.51.2

[PATCH v10 3/7] rust: error: add EDEADLK

[Onur Özkan]

This is needed for the ww_mutex implementation so
we can handle EDEADLK on lock attempts.

Signed-off-by: Onur Özkan <work@onurozkan.dev>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
---
 rust/kernel/error.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index 258b12afdcba..c2b95db23abc 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -66,6 +66,7 @@ macro_rules! declare_err {
     declare_err!(EPIPE, "Broken pipe.");
     declare_err!(EDOM, "Math argument out of domain of func.");
     declare_err!(ERANGE, "Math result not representable.");
+    declare_err!(EDEADLK, "Resource deadlock avoided.");
     declare_err!(EOVERFLOW, "Value too large for defined data type.");
     declare_err!(ETIMEDOUT, "Connection timed out.");
     declare_err!(ERESTARTSYS, "Restart the system call.");
-- 
2.51.2

[PATCH v10 4/7] rust: implement Class for ww_class support

[Onur Özkan]

Adds the Class type, the first step in supporting
ww_mutex in Rust. Class represents ww_class, used
for deadlock avoidance for supporting both wait-die
and wound-wait semantics.

Also adds the define_class macro for safely declaring
static instances.

Signed-off-by: Onur Özkan <work@onurozkan.dev>
---
 rust/kernel/sync/lock.rs                |   1 +
 rust/kernel/sync/lock/ww_mutex.rs       |   7 ++
 rust/kernel/sync/lock/ww_mutex/class.rs | 139 ++++++++++++++++++++++++
 3 files changed, 147 insertions(+)
 create mode 100644 rust/kernel/sync/lock/ww_mutex.rs
 create mode 100644 rust/kernel/sync/lock/ww_mutex/class.rs

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index 46a57d1fc309..ef7f4a023177 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -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};
diff --git a/rust/kernel/sync/lock/ww_mutex.rs b/rust/kernel/sync/lock/ww_mutex.rs
new file mode 100644
index 000000000000..727c51cc73af
--- /dev/null
+++ b/rust/kernel/sync/lock/ww_mutex.rs
@@ -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;
diff --git a/rust/kernel/sync/lock/ww_mutex/class.rs b/rust/kernel/sync/lock/ww_mutex/class.rs
new file mode 100644
index 000000000000..d57478f33659
--- /dev/null
+++ b/rust/kernel/sync/lock/ww_mutex/class.rs
@@ -0,0 +1,139 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Provides [`Class`] to group wound/wait mutexes to be acquired together
+//! and specifies which deadlock avoidance algorithm to use (e.g., wound-wait
+//! or wait-die).
+//!
+//! The [`define_ww_class!`] and [`define_wd_class!`] macros provide safe
+//! ways to create classes.
+
+use crate::bindings;
+use crate::prelude::*;
+use crate::types::Opaque;
+
+/// Defines a static wound-wait [`Class`].
+///
+/// # Examples
+///
+/// ```
+/// use kernel::define_ww_class;
+///
+/// define_ww_class!(SOME_WW_CLASS);
+/// ```
+#[macro_export]
+macro_rules! define_ww_class {
+    ($name:ident) => {
+        static $name: $crate::sync::lock::ww_mutex::Class =
+            // SAFETY: This is `static`, so address is fixed and won't move.
+            unsafe {
+                $crate::sync::lock::ww_mutex::Class::new_unpinned(
+                    $crate::c_str!(::core::stringify!($name)),
+                    false,
+                )
+            };
+    };
+}
+
+/// Defines a static wait-die [`Class`].
+///
+/// # Examples
+///
+/// ```
+/// use kernel::define_wd_class;
+///
+/// define_wd_class!(SOME_WD_CLASS);
+/// ```
+#[macro_export]
+macro_rules! define_wd_class {
+    ($name:ident) => {
+        static $name: $crate::sync::lock::ww_mutex::Class =
+            // SAFETY: This is `static`, so address is fixed and won't move.
+            unsafe {
+                $crate::sync::lock::ww_mutex::Class::new_unpinned(
+                    $crate::c_str!(::core::stringify!($name)),
+                    true,
+                )
+            };
+    };
+}
+
+/// Used to group mutexes together for deadlock avoidance.
+///
+/// All mutexes that might be acquired together should use the same class.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::{define_ww_class, define_wd_class};
+///
+/// define_ww_class!(SOME_WW_CLASS);
+/// define_wd_class!(SOME_WD_CLASS);
+///
+/// # Ok::<(), Error>(())
+/// ```
+#[pin_data]
+#[repr(transparent)]
+pub struct Class {
+    #[pin]
+    pub(super) inner: Opaque<bindings::ww_class>,
+}
+
+impl Class {
+    /// Creates an unpinned [`Class`].
+    ///
+    /// You should prefer using [`define_ww_class!`] and [`define_wd_class!`]
+    /// macros. This function is `pub` only so that those macros can use it.
+    /// The alternative would be to expose the private fields of [`Class`]
+    /// which is less desirable.
+    ///
+    /// # Safety
+    ///
+    /// Caller must guarantee that the returned value must be pinned before
+    /// its first use.
+    pub const unsafe fn new_unpinned(name: &'static CStr, is_wait_die: bool) -> Self {
+        Class {
+            inner: Opaque::new(bindings::ww_class {
+                stamp: bindings::atomic_long_t { counter: 0 },
+                acquire_name: name.as_ptr().cast(),
+                mutex_name: name.as_ptr().cast(),
+                is_wait_die: is_wait_die as u32,
+                // TODO: Replace with `bindings::lock_class_key::default()` once
+                // stabilized for `const`.
+                //
+                // SAFETY: This is always zero-initialized when defined with
+                // `DEFINE_WD_CLASS` globally on C side.
+                //
+                // For reference, see __WW_CLASS_INITIALIZER() in
+                // "include/linux/ww_mutex.h".
+                acquire_key: unsafe { core::mem::zeroed() },
+                // TODO: Replace with `bindings::lock_class_key::default()` once
+                // stabilized for `const`.
+                //
+                // SAFETY: This is always zero-initialized when defined with
+                // `DEFINE_WD_CLASS` globally on C side.
+                //
+                // For reference, see __WW_CLASS_INITIALIZER() in
+                // "include/linux/ww_mutex.h".
+                mutex_key: unsafe { core::mem::zeroed() },
+            }),
+        }
+    }
+
+    /// Creates a [`Class`] from a raw pointer.
+    ///
+    /// This function is intended for interoperability with C code.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `ptr` points to the `inner` field of
+    /// [`Class`] and that it remains valid for the lifetime `'a`.
+    pub const unsafe fn from_raw<'a>(ptr: *mut bindings::ww_class) -> &'a Self {
+        // SAFETY: By the safety contract, `ptr` is valid to construct `Class`.
+        unsafe { &*ptr.cast() }
+    }
+}
+
+// SAFETY: [`Class`] is set up once and never modified. It's fine to share it across threads.
+unsafe impl Sync for Class {}
+// SAFETY: Doesn't hold anything thread-specific. It's safe to send to other threads.
+unsafe impl Send for Class {}
-- 
2.51.2

[PATCH v10 5/7] rust: ww_mutex: add Mutex, AcquireCtx and MutexGuard

[Onur Özkan]

Covers the entire low-level locking API (lock, try_lock,
slow path, interruptible variants) and integration with
kernel bindings.

Signed-off-by: Onur Özkan <work@onurozkan.dev>
---
 rust/kernel/sync/lock/ww_mutex.rs             | 431 ++++++++++++++++++
 rust/kernel/sync/lock/ww_mutex/acquire_ctx.rs | 172 +++++++
 2 files changed, 603 insertions(+)
 create mode 100644 rust/kernel/sync/lock/ww_mutex/acquire_ctx.rs

diff --git a/rust/kernel/sync/lock/ww_mutex.rs b/rust/kernel/sync/lock/ww_mutex.rs
index 727c51cc73af..e36a0204a00e 100644
--- a/rust/kernel/sync/lock/ww_mutex.rs
+++ b/rust/kernel/sync/lock/ww_mutex.rs
@@ -1,7 +1,438 @@
 // 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::error::to_result;
+use crate::prelude::*;
+use crate::types::{NotThreadSafe, Opaque};
+use crate::{bindings, container_of};
+
+use core::cell::UnsafeCell;
+use core::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;
+/// use kernel::sync::Arc;
+/// use kernel::sync::lock::ww_mutex::{AcquireCtx, Class, Mutex};
+/// 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)?;
+///
+/// let guard = 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)
+    }
+
+    /// Locks this [`Mutex`] without [`AcquireCtx`] using the slow path.
+    ///
+    /// This function should be used when [`Self::lock`] fails (typically due
+    /// to a potential deadlock).
+    pub fn lock_slow(&self) -> Result<MutexGuard<'_, T>> {
+        lock_common(self, None, LockKind::Slow)
+    }
+
+    /// Similar to [`Self::lock_slow`], but can be interrupted by signals.
+    pub fn lock_slow_interruptible(&self) -> Result<MutexGuard<'_, T>> {
+        lock_common(self, None, LockKind::SlowInterruptible)
+    }
+
+    /// 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` can be shared across threads if the protected
+// data `T` can be.
+unsafe impl<T: ?Sized + Send + Sync> 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`.
+    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,
+    /// Used in slow path after deadlock detection.
+    Slow,
+    /// Slow path but interruptible.
+    SlowInterruptible,
+    /// 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::Slow => {
+            // 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.
+            unsafe { bindings::ww_mutex_lock_slow(mutex_ptr, ctx_ptr) };
+        }
+        LockKind::SlowInterruptible => {
+            // 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_slow_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 crate::prelude::*;
+    use crate::sync::Arc;
+    use crate::{define_wd_class, define_ww_class};
+
+    use super::*;
+
+    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)?;
+
+        let guard = ctx.lock(&mutex)?;
+        assert_eq!(*guard, 42);
+
+        // Drop the lock.
+        drop(guard);
+
+        let mut guard = 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.
+        let guard = ctx.try_lock(&mutex)?;
+        assert_eq!(*guard, 123);
+
+        // Now it should fail immediately as it's already locked.
+        assert!(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());
+
+        let guard = 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.
+        let guard1 = ctx.lock(&mutex1)?;
+        let guard2 = ctx.lock(&mutex2)?;
+
+        assert_eq!(*guard1, 1);
+        assert_eq!(*guard2, 2);
+
+        // SAFETY: It's called exactly once here and nowhere else.
+        unsafe { ctx.done() };
+
+        // We shouldn't be able to lock once it's `done`.
+        assert!(ctx.lock(&mutex1).is_err());
+        assert!(ctx.lock(&mutex2).is_err());
+
+        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_with_unlocked_mutex() -> Result {
+        let mutex = Arc::pin_init(Mutex::new((), &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+
+        assert!(!mutex.is_locked());
+
+        // SAFETY: `mutex` remains valid for the duration of this test.
+        match unsafe { MutexGuard::from_raw(mutex.inner.get()) } {
+            // Should fail with `EINVAL` because the mutex is not locked.
+            Err(e) => assert_eq!(e, EINVAL),
+            _ => unreachable!(),
+        };
+
+        Ok(())
+    }
+}
diff --git a/rust/kernel/sync/lock/ww_mutex/acquire_ctx.rs b/rust/kernel/sync/lock/ww_mutex/acquire_ctx.rs
new file mode 100644
index 000000000000..4b773c76bd2c
--- /dev/null
+++ b/rust/kernel/sync/lock/ww_mutex/acquire_ctx.rs
@@ -0,0 +1,172 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Provides [`AcquireCtx`] for managing multiple wound/wait
+//! mutexes from the same [`Class`].
+
+use crate::bindings;
+use crate::prelude::*;
+use crate::types::Opaque;
+
+use core::marker::PhantomData;
+
+use super::{lock_common, Class, LockKind, Mutex, MutexGuard};
+
+/// Groups multiple [`Mutex`]es for deadlock avoidance when acquired
+/// with the same [`Class`].
+///
+/// # Examples
+///
+/// ```
+/// use kernel::sync::lock::ww_mutex::{Class, AcquireCtx, Mutex};
+/// use kernel::define_ww_class;
+/// use kernel::sync::Arc;
+/// use pin_init::stack_pin_init;
+///
+/// define_ww_class!(SOME_WW_CLASS);
+///
+/// // Create mutexes.
+/// let mutex1 = Arc::pin_init(Mutex::new(1, &SOME_WW_CLASS), GFP_KERNEL)?;
+/// let mutex2 = Arc::pin_init(Mutex::new(2, &SOME_WW_CLASS), GFP_KERNEL)?;
+///
+/// // Create acquire context for deadlock avoidance.
+/// let ctx = KBox::pin_init(AcquireCtx::new(&SOME_WW_CLASS), GFP_KERNEL)?;
+///
+/// let guard1 = ctx.lock(&mutex1)?;
+/// let guard2 = ctx.lock(&mutex2)?;
+///
+/// // Mark acquisition phase as complete.
+/// // SAFETY: It's called exactly once here and nowhere else.
+/// unsafe { ctx.done() };
+///
+/// # Ok::<(), Error>(())
+/// ```
+#[pin_data(PinnedDrop)]
+#[repr(transparent)]
+pub struct AcquireCtx<'a> {
+    #[pin]
+    pub(super) inner: Opaque<bindings::ww_acquire_ctx>,
+    _p: PhantomData<&'a Class>,
+}
+
+impl<'class> AcquireCtx<'class> {
+    /// Initializes a new [`AcquireCtx`] with the given [`Class`].
+    pub fn new(class: &'class Class) -> impl PinInit<Self> {
+        let class_ptr = class.inner.get();
+        pin_init!(AcquireCtx {
+            inner <- Opaque::ffi_init(|slot: *mut bindings::ww_acquire_ctx| {
+                // SAFETY: `class` is valid for the lifetime `'class` captured
+                // by `AcquireCtx`.
+                unsafe { bindings::ww_acquire_init(slot, class_ptr) }
+            }),
+            _p: PhantomData
+        })
+    }
+
+    /// Creates a [`AcquireCtx`] 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 the `inner` field
+    /// of [`AcquireCtx`] and that it remains valid for the lifetime `'a`.
+    pub unsafe fn from_raw<'a>(ptr: *mut bindings::ww_acquire_ctx) -> &'a Self {
+        // SAFETY: By the safety contract, `ptr` is valid to construct `AcquireCtx`.
+        unsafe { &*ptr.cast() }
+    }
+
+    /// Marks the end of the acquire phase.
+    ///
+    /// Calling this function is optional. It is just useful to document
+    /// the code and clearly designated the acquire phase from actually
+    /// using the locked data structures.
+    ///
+    /// After calling this function, no more mutexes can be acquired with
+    /// this context.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that this function is called only once
+    /// and after calling it, no further mutexes are acquired using
+    /// this context.
+    pub unsafe fn done(&self) {
+        // SAFETY: By the safety contract, the caller guarantees that this
+        // function is called only once.
+        unsafe { bindings::ww_acquire_done(self.inner.get()) };
+    }
+
+    /// Re-initializes the [`AcquireCtx`].
+    ///
+    /// Must be called after releasing all locks when [`EDEADLK`] occurs.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure no locks are held in this [`AcquireCtx`].
+    pub unsafe fn reinit(self: Pin<&mut Self>) {
+        let ctx = self.inner.get();
+
+        // SAFETY: `ww_class` is always a valid pointer in properly initialized
+        // `AcquireCtx`.
+        let class_ptr = unsafe { (*ctx).ww_class };
+
+        // SAFETY:
+        //  - Lifetime of any guard (which hold an immutable borrow of `self`) cannot overlap
+        //    with the execution of this function. This enforces that all locks acquired via
+        //    this context have been released.
+        //
+        //  - `ctx` is guaranteed to be initialized because `ww_acquire_fini`
+        //    can only be called from the `Drop` implementation.
+        //
+        //  - `ww_acquire_fini` is safe to call on an initialized context.
+        unsafe { bindings::ww_acquire_fini(ctx) };
+
+        // SAFETY: `ww_acquire_init` is safe to call with valid pointers
+        // to initialize an uninitialized context.
+        unsafe { bindings::ww_acquire_init(ctx, class_ptr) };
+    }
+
+    /// Locks the given [`Mutex`] on this [`AcquireCtx`].
+    pub fn lock<'a, T>(&'a self, mutex: &'a Mutex<'a, T>) -> Result<MutexGuard<'a, T>> {
+        lock_common(mutex, Some(self), LockKind::Regular)
+    }
+
+    /// Similar to [`Self::lock`], but can be interrupted by signals.
+    pub fn lock_interruptible<'a, T>(
+        &'a self,
+        mutex: &'a Mutex<'a, T>,
+    ) -> Result<MutexGuard<'a, T>> {
+        lock_common(mutex, Some(self), LockKind::Interruptible)
+    }
+
+    /// Locks the given [`Mutex`] on this [`AcquireCtx`] using the slow path.
+    ///
+    /// This function should be used when [`Self::lock`] fails (typically due
+    /// to a potential deadlock).
+    pub fn lock_slow<'a, T>(&'a self, mutex: &'a Mutex<'a, T>) -> Result<MutexGuard<'a, T>> {
+        lock_common(mutex, Some(self), LockKind::Slow)
+    }
+
+    /// Similar to [`Self::lock_slow`], but can be interrupted by signals.
+    pub fn lock_slow_interruptible<'a, T>(
+        &'a self,
+        mutex: &'a Mutex<'a, T>,
+    ) -> Result<MutexGuard<'a, T>> {
+        lock_common(mutex, Some(self), LockKind::SlowInterruptible)
+    }
+
+    /// Tries to lock the [`Mutex`] on this [`AcquireCtx`] without blocking.
+    ///
+    /// Unlike [`Self::lock`], no deadlock handling is performed.
+    pub fn try_lock<'a, T>(&'a self, mutex: &'a Mutex<'a, T>) -> Result<MutexGuard<'a, T>> {
+        lock_common(mutex, Some(self), LockKind::Try)
+    }
+}
+
+#[pinned_drop]
+impl PinnedDrop for AcquireCtx<'_> {
+    fn drop(self: Pin<&mut Self>) {
+        // SAFETY: Given the lifetime bounds we know no locks are held,
+        // so calling `ww_acquire_fini` is safe.
+        unsafe { bindings::ww_acquire_fini(self.inner.get()) };
+    }
+}
-- 
2.51.2

[PATCH v10 6/7] rust: ww_mutex: implement LockSet

[Onur Özkan]

LockSet is a high-level and safe API built on top of
ww_mutex which provides a safe and easy to use API
while keeping the ww_mutex semantics.

When EDEADLK is hit it drops all held locks, resets
the acquire context and retries the given (by the user)
locking algorithm until it succeeds.

Signed-off-by: Onur Özkan <work@onurozkan.dev>
---
 rust/kernel/sync/lock/ww_mutex.rs          |   6 +
 rust/kernel/sync/lock/ww_mutex/lock_set.rs | 370 +++++++++++++++++++++
 2 files changed, 376 insertions(+)
 create mode 100644 rust/kernel/sync/lock/ww_mutex/lock_set.rs

diff --git a/rust/kernel/sync/lock/ww_mutex.rs b/rust/kernel/sync/lock/ww_mutex.rs
index e36a0204a00e..0c12dfc05f22 100644
--- a/rust/kernel/sync/lock/ww_mutex.rs
+++ b/rust/kernel/sync/lock/ww_mutex.rs
@@ -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::error::to_result;
@@ -18,9 +22,11 @@
 
 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`].
diff --git a/rust/kernel/sync/lock/ww_mutex/lock_set.rs b/rust/kernel/sync/lock/ww_mutex/lock_set.rs
new file mode 100644
index 000000000000..db5ca4fe7cb4
--- /dev/null
+++ b/rust/kernel/sync/lock/ww_mutex/lock_set.rs
@@ -0,0 +1,370 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Provides [`LockSet`] which automatically detects [`EDEADLK`],
+//! releases all locks, resets the state and retries the user
+//! supplied locking algorithm until success.
+
+use super::{AcquireCtx, Class, Mutex};
+use crate::bindings;
+use crate::prelude::*;
+use crate::types::NotThreadSafe;
+use core::ptr::NonNull;
+
+/// A tracked set of [`Mutex`] locks acquired under the same [`Class`].
+///
+/// It ensures proper cleanup and retry mechanism on deadlocks and provides
+/// safe access to locked data via [`LockSet::with_locked`].
+///
+/// Typical usage is through [`LockSet::lock_all`], which retries a
+/// user supplied locking algorithm until it succeeds without deadlock.
+pub struct LockSet<'a> {
+    acquire_ctx: Pin<KBox<AcquireCtx<'a>>>,
+    taken: KVec<RawGuard>,
+}
+
+/// Used by [`LockSet`] to track acquired locks.
+///
+/// This type is strictly crate-private and must never be exposed
+/// outside this crate.
+struct RawGuard {
+    mutex_ptr: NonNull<bindings::ww_mutex>,
+    _not_send: NotThreadSafe,
+}
+
+impl Drop for RawGuard {
+    fn drop(&mut self) {
+        // SAFETY: `mutex_ptr` originates from a locked `Mutex` and remains
+        // valid for the lifetime of this guard, so unlocking here is sound.
+        unsafe { bindings::ww_mutex_unlock(self.mutex_ptr.as_ptr()) };
+    }
+}
+
+impl<'a> Drop for LockSet<'a> {
+    fn drop(&mut self) {
+        self.release_all_locks();
+    }
+}
+
+impl<'a> LockSet<'a> {
+    /// Creates a new [`LockSet`] with the given [`Class`].
+    ///
+    /// All locks taken through this [`LockSet`] must belong to the
+    /// same [`Class`].
+    pub fn new(class: &'a Class) -> Result<Self> {
+        Ok(Self {
+            acquire_ctx: KBox::pin_init(AcquireCtx::new(class), GFP_KERNEL)?,
+            taken: KVec::new(),
+        })
+    }
+
+    /// Creates a new [`LockSet`] using an existing [`AcquireCtx`].
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `acquire_ctx` is properly initialized
+    /// and holds no [`Mutex`]es.
+    pub unsafe fn new_with_acquire_ctx(acquire_ctx: Pin<KBox<AcquireCtx<'a>>>) -> Self {
+        Self {
+            acquire_ctx,
+            taken: KVec::new(),
+        }
+    }
+
+    /// Attempts to lock the given [`Mutex`] and stores a guard for it.
+    pub fn lock<T>(&mut self, mutex: &'a Mutex<'a, T>) -> Result {
+        let guard = self.acquire_ctx.lock(mutex)?;
+
+        self.taken.push(
+            RawGuard {
+                // SAFETY: We just locked it above so it's a valid pointer.
+                mutex_ptr: unsafe { NonNull::new_unchecked(guard.mutex.inner.get()) },
+                _not_send: NotThreadSafe,
+            },
+            GFP_KERNEL,
+        )?;
+
+        // Avoid unlocking here; `release_all_locks` (also run by `Drop`)
+        // performs the unlock for `LockSet`.
+        core::mem::forget(guard);
+
+        Ok(())
+    }
+
+    /// Runs `locking_algorithm` until success with retrying on deadlock.
+    ///
+    /// `locking_algorithm` should attempt to acquire all needed locks.
+    /// If [`EDEADLK`] is detected, this function will roll back, reset
+    /// the context and retry automatically.
+    ///
+    /// Once all locks are acquired successfully, `on_all_locks_taken` is
+    /// invoked for exclusive access to the locked values. Afterwards, all
+    /// locks are released.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use kernel::alloc::KBox;
+    /// use kernel::define_ww_class;
+    /// use kernel::prelude::*;
+    /// use kernel::sync::Arc;
+    /// use kernel::sync::lock::ww_mutex::{LockSet, Mutex};
+    /// use pin_init::stack_pin_init;
+    ///
+    /// define_ww_class!(SOME_WOUND_WAIT_CLASS);
+    ///
+    /// let mutex1 = Arc::pin_init(Mutex::new(0, &SOME_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+    /// let mutex2 = Arc::pin_init(Mutex::new(0, &SOME_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+    /// let mut lock_set = KBox::pin_init(LockSet::new(&SOME_WOUND_WAIT_CLASS)?, GFP_KERNEL)?;
+    ///
+    /// lock_set.lock_all(
+    ///     // `locking_algorithm` closure
+    ///     |lock_set| {
+    ///         lock_set.lock(&mutex1)?;
+    ///         lock_set.lock(&mutex2)?;
+    ///
+    ///         Ok(())
+    ///     },
+    ///     // `on_all_locks_taken` closure
+    ///     |lock_set| {
+    ///         // Safely mutate both values while holding the locks.
+    ///         lock_set.with_locked(&mutex1, |v| *v += 1)?;
+    ///         lock_set.with_locked(&mutex2, |v| *v += 1)?;
+    ///
+    ///         Ok(())
+    ///     },
+    /// )?;
+    ///
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub fn lock_all<T, Y, Z>(
+        &mut self,
+        mut locking_algorithm: T,
+        mut on_all_locks_taken: Y,
+    ) -> Result<Z>
+    where
+        T: FnMut(&mut LockSet<'a>) -> Result,
+        Y: FnMut(&mut LockSet<'a>) -> Result<Z>,
+    {
+        loop {
+            match locking_algorithm(self) {
+                Ok(()) => {
+                    // All locks in `locking_algorithm` succeeded.
+                    // The user can now safely use them in `on_all_locks_taken`.
+                    let res = on_all_locks_taken(self);
+                    self.release_all_locks();
+
+                    return res;
+                }
+                Err(e) if e == EDEADLK => {
+                    // Deadlock detected, retry from scratch.
+                    self.cleanup_on_deadlock();
+                    continue;
+                }
+                Err(e) => {
+                    self.release_all_locks();
+                    return Err(e);
+                }
+            }
+        }
+    }
+
+    /// Executes `access` with a mutable reference to the data behind [`Mutex`].
+    ///
+    /// Fails with [`EINVAL`] if the [`Mutex`] was not locked in this [`LockSet`].
+    pub fn with_locked<T: Unpin, Y>(
+        &mut self,
+        mutex: &'a Mutex<'a, T>,
+        access: impl for<'b> FnOnce(&'b mut T) -> Y,
+    ) -> Result<Y> {
+        let mutex_ptr = mutex.inner.get();
+
+        if self
+            .taken
+            .iter()
+            .any(|guard| guard.mutex_ptr.as_ptr() == mutex_ptr)
+        {
+            // SAFETY: We hold the lock corresponding to `mutex`, so we have
+            // exclusive access to its protected data.
+            let value = unsafe { &mut *mutex.data.get() };
+            Ok(access(value))
+        } else {
+            // `mutex` isn't locked in this `LockSet`.
+            Err(EINVAL)
+        }
+    }
+
+    /// Releases all currently held locks in this [`LockSet`].
+    fn release_all_locks(&mut self) {
+        // `Drop` implementation of the `RawGuard` takes care of the unlocking.
+        self.taken.clear();
+    }
+
+    /// Resets this [`LockSet`] after a deadlock detection.
+    ///
+    /// Drops all held locks and reinitializes the [`AcquireCtx`].
+    ///
+    /// It is intended to be used for internal implementation only.
+    fn cleanup_on_deadlock(&mut self) {
+        self.release_all_locks();
+
+        // SAFETY: We released all the locks just above.
+        unsafe { self.acquire_ctx.as_mut().reinit() };
+    }
+}
+
+#[kunit_tests(rust_kernel_lock_set)]
+mod tests {
+    use crate::prelude::*;
+    use crate::sync::Arc;
+    use crate::{define_wd_class, define_ww_class};
+
+    use super::*;
+
+    define_ww_class!(TEST_WOUND_WAIT_CLASS);
+    define_wd_class!(TEST_WAIT_DIE_CLASS);
+
+    #[test]
+    fn test_lock_set_basic_lock_unlock() -> Result {
+        let mutex = Arc::pin_init(Mutex::new(10, &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+        let mut lock_set = KBox::pin_init(LockSet::new(&TEST_WOUND_WAIT_CLASS)?, GFP_KERNEL)?;
+
+        lock_set.lock(&mutex)?;
+
+        lock_set.with_locked(&mutex, |v| {
+            assert_eq!(*v, 10);
+        })?;
+
+        lock_set.release_all_locks();
+        assert!(!mutex.is_locked());
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_lock_set_with_locked_mutates_data() -> Result {
+        let mutex = Arc::pin_init(Mutex::new(5, &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+        let mut lock_set = KBox::pin_init(LockSet::new(&TEST_WOUND_WAIT_CLASS)?, GFP_KERNEL)?;
+
+        lock_set.lock(&mutex)?;
+
+        lock_set.with_locked(&mutex, |v| {
+            assert_eq!(*v, 5);
+            // Increment the value.
+            *v += 7;
+        })?;
+
+        lock_set.with_locked(&mutex, |v| {
+            // Check that mutation took effect.
+            assert_eq!(*v, 12);
+        })?;
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_lock_all_success() -> Result {
+        let mutex1 = Arc::pin_init(Mutex::new(1, &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+        let mutex2 = Arc::pin_init(Mutex::new(2, &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+        let mut lock_set = KBox::pin_init(LockSet::new(&TEST_WOUND_WAIT_CLASS)?, GFP_KERNEL)?;
+
+        let res = lock_set.lock_all(
+            // `locking_algorithm` closure
+            |lock_set| {
+                let _ = lock_set.lock(&mutex1)?;
+                let _ = lock_set.lock(&mutex2)?;
+                Ok(())
+            },
+            // `on_all_locks_taken` closure
+            |lock_set| {
+                lock_set.with_locked(&mutex1, |v| *v += 10)?;
+                lock_set.with_locked(&mutex2, |v| *v += 20)?;
+                Ok((
+                    lock_set.with_locked(&mutex1, |v| *v)?,
+                    lock_set.with_locked(&mutex2, |v| *v)?,
+                ))
+            },
+        )?;
+
+        assert_eq!(res, (11, 22));
+        assert!(!mutex1.is_locked());
+        assert!(!mutex2.is_locked());
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_with_different_input_type() -> Result {
+        let mutex1 = Arc::pin_init(Mutex::new(1, &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+        let mutex2 = Arc::pin_init(Mutex::new("hello", &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+        let mut lock_set = KBox::pin_init(LockSet::new(&TEST_WOUND_WAIT_CLASS)?, GFP_KERNEL)?;
+
+        lock_set.lock_all(
+            // `locking_algorithm` closure
+            |lock_set| {
+                lock_set.lock(&mutex1)?;
+                lock_set.lock(&mutex2)?;
+
+                Ok(())
+            },
+            // `on_all_locks_taken` closure
+            |lock_set| {
+                lock_set.with_locked(&mutex1, |v| assert_eq!(*v, 1))?;
+                lock_set.with_locked(&mutex2, |v| assert_eq!(*v, "hello"))?;
+                Ok(())
+            },
+        )?;
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_lock_all_retries_on_deadlock() -> Result {
+        let mutex = Arc::pin_init(Mutex::new(99, &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+        let mut lock_set = KBox::pin_init(LockSet::new(&TEST_WOUND_WAIT_CLASS)?, GFP_KERNEL)?;
+        let mut first_try = true;
+
+        let res = lock_set.lock_all(
+            // `locking_algorithm` closure
+            |lock_set| {
+                if first_try {
+                    first_try = false;
+                    // Simulate deadlock on first attempt.
+                    return Err(EDEADLK);
+                }
+                lock_set.lock(&mutex)
+            },
+            // `on_all_locks_taken` closure
+            |lock_set| {
+                lock_set.with_locked(&mutex, |v| {
+                    *v += 1;
+                    *v
+                })
+            },
+        )?;
+
+        assert_eq!(res, 100);
+        Ok(())
+    }
+
+    #[test]
+    fn test_with_locked_on_unlocked_mutex() -> Result {
+        let mutex = Arc::pin_init(Mutex::new(5, &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+        let mut lock_set = KBox::pin_init(LockSet::new(&TEST_WOUND_WAIT_CLASS)?, GFP_KERNEL)?;
+
+        let ecode = lock_set.with_locked(&mutex, |_v| {}).unwrap_err();
+        assert_eq!(EINVAL, ecode);
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_with_different_classes() -> Result {
+        let mutex = Arc::pin_init(Mutex::new(5, &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
+        let mut lock_set = KBox::pin_init(LockSet::new(&TEST_WAIT_DIE_CLASS)?, GFP_KERNEL)?;
+
+        let ecode = lock_set.lock(&mutex).unwrap_err();
+        assert_eq!(EINVAL, ecode);
+
+        Ok(())
+    }
+}
-- 
2.51.2

[PATCH v10 7/7] MAINTAINERS: add Onur Özkan as WW MUTEX maintainer

[Onur Özkan]

Add myself as a WW MUTEX maintainer to reflect ongoing
work and future maintenance of WW MUTEX.

Signed-off-by: Onur Özkan <work@onurozkan.dev>
---
 MAINTAINERS | 1 +
 1 file changed, 1 insertion(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index d245b7b38b21..10eeeaf0ccb6 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -14711,6 +14711,7 @@ M:	Peter Zijlstra <peterz@infradead.org>
 M:	Ingo Molnar <mingo@redhat.com>
 M:	Will Deacon <will@kernel.org>
 M:	Boqun Feng <boqun.feng@gmail.com> (LOCKDEP & RUST)
+M:	Onur Özkan <work@onurozkan.dev> (WW MUTEX)
 R:	Waiman Long <longman@redhat.com>
 L:	linux-kernel@vger.kernel.org
 S:	Maintained
-- 
2.51.2

Re: [PATCH v10 6/7] rust: ww_mutex: implement LockSet

[kernel test robot]

Hi Onur,

kernel test robot noticed the following build warnings:

[auto build test WARNING on tip/locking/core]
[also build test WARNING on rust/rust-next linus/master v6.19-rc3 next-20251219]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Onur-zkan/rust-add-C-wrappers-for-ww_mutex-inline-functions/20260103-153912
base:   tip/locking/core
patch link:    https://lore.kernel.org/r/20260103073554.34855-7-work%40onurozkan.dev
patch subject: [PATCH v10 6/7] rust: ww_mutex: implement LockSet
config: x86_64-rhel-9.4-rust (https://download.01.org/0day-ci/archive/20260103/202601031513.bVzSj6aK-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
rustc: rustc 1.88.0 (6b00bc388 2025-06-23)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260103/202601031513.bVzSj6aK-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202601031513.bVzSj6aK-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> warning: this let-binding has unit value
   --> rust/kernel/sync/lock/ww_mutex/lock_set.rs:273:17
   |
   273 |                 let _ = lock_set.lock(&mutex1)?;
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: omit the `let` binding: `lock_set.lock(&mutex1)?;`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#let_unit_value
   = note: `-W clippy::let-unit-value` implied by `-W clippy::all`
   = help: to override `-W clippy::all` add `#[allow(clippy::let_unit_value)]`
--
>> warning: matching over `()` is more explicit
   --> rust/kernel/sync/lock/ww_mutex/lock_set.rs:273:21
   |
   273 |                 let _ = lock_set.lock(&mutex1)?;
   |                     ^ help: use `()` instead of `_`: `()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ignored_unit_patterns
   = note: requested on the command line with `-W clippy::ignored-unit-patterns`
--
>> warning: this let-binding has unit value
   --> rust/kernel/sync/lock/ww_mutex/lock_set.rs:274:17
   |
   274 |                 let _ = lock_set.lock(&mutex2)?;
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: omit the `let` binding: `lock_set.lock(&mutex2)?;`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#let_unit_value
--
>> warning: matching over `()` is more explicit
   --> rust/kernel/sync/lock/ww_mutex/lock_set.rs:274:21
   |
   274 |                 let _ = lock_set.lock(&mutex2)?;
   |                     ^ help: use `()` instead of `_`: `()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ignored_unit_patterns

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v10 1/7] rust: add C wrappers for ww_mutex inline functions

[Daniel Almeida]

Hi Onur,

Sorry for the delay, I’m finally getting back to this series.


> On 3 Jan 2026, at 04:35, Onur Özkan <work@onurozkan.dev> wrote:
> 
> Some of the kernel's `ww_mutex` functions are implemented as
> `static inline`, so they are inaccessible from Rust as bindgen
> can't generate code on them. This patch provides C function wrappers
> around these inline implementations, so bindgen can see them and
> generate the corresponding Rust code.
> 
> Signed-off-by: Onur Özkan <work@onurozkan.dev>

My comment remains the same as v8 [0]: did you forget to pick up tags? There’s an r-b here in v7 [1].

Or perhaps I’m missing something?

— Daniel

[0]: https://lore.kernel.org/rust-for-linux/2F879792-3C12-4C8F-8EF1-122F44EF2B19@collabora.com/
[1]: https://lore.kernel.org/rust-for-linux/34A2E775-A47E-4D4E-A292-E12489F07987@collabora.com/

Re: [PATCH v10 1/7] rust: add C wrappers for ww_mutex inline functions

[Onur Özkan]

On Tue, 3 Feb 2026 10:45:12 -0300
Daniel Almeida <daniel.almeida@collabora.com> wrote:

> Hi Onur,
> 
> Sorry for the delay, I’m finally getting back to this series.
> 

No worries, thanks for looking on this.

> 
> > On 3 Jan 2026, at 04:35, Onur Özkan <work@onurozkan.dev> wrote:
> > 
> > Some of the kernel's `ww_mutex` functions are implemented as
> > `static inline`, so they are inaccessible from Rust as bindgen
> > can't generate code on them. This patch provides C function wrappers
> > around these inline implementations, so bindgen can see them and
> > generate the corresponding Rust code.
> > 
> > Signed-off-by: Onur Özkan <work@onurozkan.dev>
> 
> My comment remains the same as v8 [0]: did you forget to pick up
> tags? There’s an r-b here in v7 [1].
> 
> Or perhaps I’m missing something?
> 

I didn't forget, the patch in this file is changed since that (see
__rust_helper prefixes).

Regards,
Onur

> — Daniel
> 
> [0]:
> https://lore.kernel.org/rust-for-linux/2F879792-3C12-4C8F-8EF1-122F44EF2B19@collabora.com/
> [1]:
> https://lore.kernel.org/rust-for-linux/34A2E775-A47E-4D4E-A292-E12489F07987@collabora.com/
> 
> 

Re: [PATCH v10 0/7] rust: add ww_mutex support

[Alice Ryhl]

On Sat, Jan 03, 2026 at 10:35:47AM +0300, Onur Özkan wrote:
> 
>  MAINTAINERS                                   |   2 +
>  include/linux/ww_mutex.h                      |   8 +-
>  rust/helpers/helpers.c                        |   1 +
>  rust/helpers/ww_mutex.c                       |  45 ++
>  rust/kernel/error.rs                          |   1 +
>  rust/kernel/sync/lock.rs                      |   1 +
>  rust/kernel/sync/lock/ww_mutex.rs             | 444 ++++++++++++++++++
>  rust/kernel/sync/lock/ww_mutex/acquire_ctx.rs | 172 +++++++
>  rust/kernel/sync/lock/ww_mutex/class.rs       | 139 ++++++
>  rust/kernel/sync/lock/ww_mutex/lock_set.rs    | 370 +++++++++++++++
>  10 files changed, 1177 insertions(+), 6 deletions(-)
>  create mode 100644 rust/helpers/ww_mutex.c
>  create mode 100644 rust/kernel/sync/lock/ww_mutex.rs
>  create mode 100644 rust/kernel/sync/lock/ww_mutex/acquire_ctx.rs
>  create mode 100644 rust/kernel/sync/lock/ww_mutex/class.rs
>  create mode 100644 rust/kernel/sync/lock/ww_mutex/lock_set.rs

Reviewed-by: Alice Ryhl <aliceryhl@google.com>