| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <20251101161056.22408-6-work@onurozkan.dev>
Date: Sat, 1 Nov 2025 19:10:55 +0300
From: Onur Özkan <work@...rozkan.dev>
To: rust-for-linux@...r.kernel.org
Cc: lossin@...nel.org,
lyude@...hat.com,
ojeda@...nel.org,
alex.gaynor@...il.com,
boqun.feng@...il.com,
gary@...yguo.net,
a.hindborg@...nel.org,
aliceryhl@...gle.com,
tmgross@...ch.edu,
dakr@...nel.org,
peterz@...radead.org,
mingo@...hat.com,
will@...nel.org,
longman@...hat.com,
felipe_life@...e.com,
daniel@...lak.dev,
bjorn3_gh@...tonmail.com,
daniel.almeida@...labora.com,
linux-kernel@...r.kernel.org,
Onur Özkan <work@...rozkan.dev>
Subject: [PATCH v7 5/6] rust: ww_mutex: implement LockSet
`LockSet` is a high-level and safe API built on top of
ww_mutex, provides a simple 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@...rozkan.dev>
---
rust/kernel/sync/lock/ww_mutex.rs | 6 +
rust/kernel/sync/lock/ww_mutex/lock_set.rs | 245 +++++++++++++++++++++
2 files changed, 251 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 2a9c1c20281b..d4c3b272912d 100644
--- a/rust/kernel/sync/lock/ww_mutex.rs
+++ b/rust/kernel/sync/lock/ww_mutex.rs
@@ -5,6 +5,10 @@
//! 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.
+//!
+//! It is recommended to use [`LockSet`] as it provides safe high-level
+//! interface that automatically handles deadlocks, retries and context
+//! management.
use crate::error::to_result;
use crate::prelude::*;
@@ -16,9 +20,11 @@
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..ae234fd1e0be
--- /dev/null
+++ b/rust/kernel/sync/lock/ww_mutex/lock_set.rs
@@ -0,0 +1,245 @@
+// 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>,
+ class: &'a Class,
+}
+
+/// 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(),
+ class,
+ })
+ }
+
+ /// Creates a new [`LockSet`] using an existing [`AcquireCtx`] and
+ /// [`Class`].
+ ///
+ /// # Safety
+ ///
+ /// The caller must ensure that `acquire_ctx` is properly initialized,
+ /// holds no mutexes and that the provided `class` matches the one used
+ /// to initialize the given `acquire_ctx`.
+ pub unsafe fn new_with_acquire_ctx(
+ acquire_ctx: Pin<KBox<AcquireCtx<'a>>>,
+ class: &'a Class,
+ ) -> Self {
+ Self {
+ acquire_ctx,
+ taken: KVec::new(),
+ class,
+ }
+ }
+
+ /// Attempts to lock a [`Mutex`] and records the guard.
+ ///
+ /// Returns [`EDEADLK`] if lock ordering would cause a deadlock.
+ ///
+ /// Returns [`EBUSY`] if `mutex` was locked outside of this [`LockSet`].
+ ///
+ /// # Safety
+ ///
+ /// The given `mutex` must be created with the [`Class`] that was used
+ /// to initialize this [`LockSet`].
+ pub unsafe fn lock<T>(&mut self, mutex: &'a Mutex<'a, T>) -> Result {
+ if mutex.is_locked()
+ && !self
+ .taken
+ .iter()
+ .any(|guard| guard.mutex_ptr.as_ptr() == mutex.inner.get())
+ {
+ return Err(EBUSY);
+ }
+
+ // SAFETY: By the safety contract, `mutex` belongs to the same `Class`
+ // as `self.acquire_ctx` does.
+ let guard = unsafe { 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::c_str;
+ /// use kernel::prelude::*;
+ /// use kernel::sync::Arc;
+ /// use kernel::sync::lock::ww_mutex::{Class, LockSet, Mutex};
+ /// use pin_init::stack_pin_init;
+ ///
+ /// stack_pin_init!(let class = Class::new_wound_wait(c_str!("test")));
+ ///
+ /// let mutex1 = Arc::pin_init(Mutex::new(0, &class), GFP_KERNEL)?;
+ /// let mutex2 = Arc::pin_init(Mutex::new(0, &class), GFP_KERNEL)?;
+ /// let mut lock_set = KBox::pin_init(LockSet::new(&class)?, GFP_KERNEL)?;
+ ///
+ /// lock_set.lock_all(
+ /// // `locking_algorithm` closure
+ /// |lock_set| {
+ /// // SAFETY: Both `lock_set` and `mutex1` uses the same class.
+ /// unsafe { lock_set.lock(&mutex1)? };
+ ///
+ /// // SAFETY: Both `lock_set` and `mutex2` uses the same class.
+ /// unsafe { 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 are passing the same `class` that was used
+ // to initialize `self.acquire_ctx`.
+ unsafe { self.acquire_ctx.as_mut().reinit(self.class) };
+ }
+}
--
2.51.2
Powered by blists - more mailing lists