linux.git/rust/kernel/sync, branch master

Merge tag 'locking-core-2026-08-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2026-08-18T20:07:17+00:00

Pull locking updates from Ingo Molnar:
 "Futexes:

   - Use runtime constants for futex_hash computation (K Prateek Nayak,
     Peter Zijlstra)

   - Optimise the size check get_futex_key() (Sebastian Andrzej Siewior)

   - Avoid private hash use-after-free on final put (Felix Hoffmann)

   - Tell kmemleak we're not leaking __futex_queues (Peter Zijlstra)

  Rust integration updates:

   - Implement refcounted interrupt disable and SpinLockIrq for Rust
     (Boqun Feng, Heiko Carstens, Joel Fernandes, Lyude Paul)

   - Rust sync: add helpers for mb, dma_mb and friends; add generic
     memory barriers and use LKMM atomics instead of Rust atomics in the
     revocable code (Gary Guo)

   - Add abstraction and integrate synchronize_rcu() (Philipp Stanner)

  Lock debugging:

   - Add qspinlock contended_release tracepoint (Dmitry Ilvokhin, Peter
     Zijlstra)

   - Enable the printing of held locks of remote running tasks and print
     task CPU (Ingo Molnar)

   - percpu-rwsem: Annotate intentional data race in readers_active_check()
     (Sun Shaojie)

  Misc fixes and updates by Boqun Feng, Peter Zijlstra, Fangrui Song,
  Naveen Kumar Chaudhary and Thomas Huth"

* tag 'locking-core-2026-08-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (44 commits)
  rust: sync: Introduce SpinLockIrq::lock_with() and friends
  rust: sync: Add SpinLockIrq
  rust: sync: Use super::* in spinlock.rs
  rust: helper: Add spin_{un,}lock_irq_{enable,disable}() helpers
  rust: Introduce interrupt module
  s390/preempt: Enable HAS_SEPARATE_PREEMPT_RESCHED_BITS
  arm64: sched/preempt: Enable HAS_SEPARATE_PREEMPT_RESCHED_BITS
  preempt: Introduce HAS_SEPARATE_PREEMPT_RESCHED_BITS
  sched: Avoid signed comparison of preempt_count() in __cant_migrate()
  sched: Remove the unused preempt_offset parameter of __cant_sleep()
  locking: Switch to _irq_{disable,enable}() variants in cleanup guards
  irq: Add KUnit test for refcounted interrupt enable/disable
  irq,spin_lock: Add counted interrupt disabling/enabling
  openrisc: Include  in smp.h
  preempt: Introduce __preempt_count_{sub,add}_return()
  preempt: Introduce HARDIRQ_DISABLE_BITS
  preempt: Track NMI nesting to separate per-CPU counter
  futex: Tell kmemleak we're not leaking __futex_queues
  x86/paravirt: Trace contended_release on unlock
  tracing/lock: Use TRACE_EVENT_FN() for contended_release
  ...

rust: sync: Introduce SpinLockIrq::lock_with() and friends

2026-08-10T10:53:11+00:00

`SpinLockIrq` and `SpinLock` use the exact same underlying C structure,
with the only real difference being that the former uses the
irq_disable() and irq_enable() variants for locking/unlocking. These
variants can introduce some minor overhead in contexts where we already
know that local processor interrupts are disabled, and as such we want a
way to be able to skip modifying processor interrupt state in said
contexts in order to avoid some overhead - just like the current C API
allows us to do.

In order to do this, we add some special functions for SpinLockIrq:
lock_with() and try_lock_with(), which allow acquiring the lock without
changing the interrupt state - as long as the caller can provide a
LocalInterruptDisabled reference to prove that local processor
interrupts have been disabled.

In some hacked-together benchmarks we ran, most of the time this did
actually seem to lead to a noticeable difference in overhead:

  From an aarch64 VM running on a MacBook M4:
    lock() when irq is disabled, 100 times cost Delta { nanos: 500 }
    lock_with() when irq is disabled, 100 times cost Delta { nanos: 292 }
    lock() when irq is enabled, 100 times cost Delta { nanos: 834 }

    lock() when irq is disabled, 100 times cost Delta { nanos: 459 }
    lock_with() when irq is disabled, 100 times cost Delta { nanos: 291 }
    lock() when irq is enabled, 100 times cost Delta { nanos: 709 }

  From an x86_64 VM (qemu/kvm) running on a i7-13700H
    lock() when irq is disabled, 100 times cost Delta { nanos: 1002 }
    lock_with() when irq is disabled, 100 times cost Delta { nanos: 729 }
    lock() when irq is enabled, 100 times cost Delta { nanos: 1516 }

    lock() when irq is disabled, 100 times cost Delta { nanos: 754 }
    lock_with() when irq is disabled, 100 times cost Delta { nanos: 966 }
    lock() when irq is enabled, 100 times cost Delta { nanos: 1227 }

    (note that there were some runs on x86_64 where lock() on irq
    disabled vs. lock_with() on irq disabled had equivalent benchmarks,
    but it very much appeared to be a minority of test runs.)

While it's not clear how this affects real-world workloads yet, let's
add this for the time being so we can find out.

This makes it so that a `SpinLockIrq` will work like a `SpinLock` if
interrupts are disabled. So a function:

        (&'a SpinLockIrq, &'a LocalInterruptDisabled) -> Guard<'a, .., SpinLockBackend>

makes sense. Note that due to `Guard` and `LocalInterruptDisabled`
having the same lifetime, interrupts cannot be enabled while the Guard
exists.

Signed-off-by: Lyude Paul 
Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260807070218.27144-19-boqun@kernel.org

rust: sync: Add SpinLockIrq

2026-08-10T10:53:10+00:00

A variant of `SpinLock` that ensures interrupts are disabled in the
critical section. `lock()` will ensure that either interrupts are
already disabled or disable them. `unlock()` will reverse the respective
operation.

[Boqun: Port to use spin_lock_irq_disable() and
spin_unlock_irq_enable()]

Signed-off-by: Lyude Paul 
Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260807070218.27144-18-boqun@kernel.org

rust: sync: Use super::* in spinlock.rs

2026-08-10T10:53:10+00:00

No functional changes.

Signed-off-by: Lyude Paul 
Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://patch.msgid.link/20260807070218.27144-17-boqun@kernel.org

rust: sync: Add abstraction for rcu_barrier()

2026-08-10T05:58:37+00:00

rcu_barrier() is a frequently used C function which is always safe to be
called.

Add a safe abstraction for rcu_barrier().

Tested-by: Daniel Almeida 
Signed-off-by: Philipp Stanner 
Acked-by: Gary Guo 
Reviewed-by: Onur Özkan 
Acked-by: Danilo Krummrich 
Link: https://patch.msgid.link/20260805145949.938505-5-phasta@kernel.org
[ Formatted documentation. Sorted tags. - Miguel ]
Signed-off-by: Miguel Ojeda

rust: types: implement ForeignOwnable for ARef

2026-08-10T05:58:27+00:00

Implement ForeignOwnable for ARef, making it possible for C code to
own an ARef.

Since ARef represents shared ownership, BorrowedMut is &T rather than
&mut T, matching the semantics of the underlying reference-counted type.

Signed-off-by: Danilo Krummrich 
Reviewed-by: Alice Ryhl 
Tested-by: Daniel Almeida 
Signed-off-by: Philipp Stanner 
Acked-by: Danilo Krummrich 
Link: https://patch.msgid.link/20260805145949.938505-4-phasta@kernel.org
[ Relaxed `'static` bound and added `#[inline]` as discussed. Added
  the submitter's Signed-off-by tag. - Miguel ]
Signed-off-by: Miguel Ojeda

rust: sync: improve `Arc` documentation links

2026-08-10T04:44:10+00:00

The `Arc` documentation has a few mentions that do not follow the
surrounding style: a plain `Arc` without an intra-doc link and a
lower-case "arc".

Use intra-doc links for rustdoc references to `Arc` and spell internal
comments consistently as `Arc`, matching nearby docs.

Suggested-by: Miguel Ojeda 
Link: https://github.com/Rust-for-Linux/linux/issues/1240
Signed-off-by: Harish C S 
Acked-by: Boqun Feng 
Link: https://patch.msgid.link/20260711145033.39649-1-harish.cs.ss24@gmail.com
Signed-off-by: Miguel Ojeda

rust: treewide: replace `__pinned_init` with `raw_[try_]init`

2026-08-05T10:36:18+00:00

The `__init` method is not designed to be a public API (existence of "__"
is a hint for this); replace users with `pin_init::raw_[try_]init` which
does the same thing.

There are a few users of `__init` which are replaced as well.

Acked-by: Miguel Ojeda 
Acked-by: Danilo Krummrich 
Link: https://patch.msgid.link/20260729-merge-init-v2-4-26adf47109e7@garyguo.net
Signed-off-by: Gary Guo

rust: sync: Add generic memory barriers

2026-08-04T12:52:54+00:00

Implement a generic interface for memory barriers (full system/DMA/SMP).
The interface uses a parameter to force user to specify their intent
with barriers.

Provide `Read`, `Write`, `Full` orderings which map to the existing
`rmb()`, `wmb()` and `mb()`. Generic is used here instead of providing
individual standalone functions to reduce code duplication; for example,
the `CONFIG_SMP` check in `smp_mb` is uniformly implemented for all SMP
barriers. This could extend to `virt_mb`'s if they're introduced in the
future. It would also make it easier if new ordering types are
introduced in the future (e.g. `Acquire`, `Release`).

Signed-off-by: Gary Guo 
Signed-off-by: Boqun Feng 
Link: https://patch.msgid.link/20260609-rust-barrier-v2-2-30fcc48e1cd0@garyguo.net

rust: sync: Use safe synchronize_rcu() abstraction in poll

2026-08-04T12:52:54+00:00

We now have a safe wrapper for the foreign function synchronize_rcu().

Use it in poll.rs.

Signed-off-by: Philipp Stanner 
Reviewed-by: Alice Ryhl 
Reviewed-by: Onur Özkan 
Reviewed-by: Danilo Krummrich 
Reviewed-by: Gary Guo 
Signed-off-by: Boqun Feng 
Link: https://patch.msgid.link/20260624150704.1504001-5-phasta@kernel.org