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

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 <linux/cpumask.h> 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
  ...

1 files changed, 27 insertions, 9 deletions

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 2d4c5bab5af8..25d77d4a1061 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -787,17 +787,33 @@ static void lockdep_print_held_locks(struct task_struct *p)
 {
 	int i, depth = READ_ONCE(p->lockdep_depth);
 
-	if (!depth)
-		printk("no locks held by %s/%d.\n", p->comm, task_pid_nr(p));
-	else
-		printk("%d lock%s held by %s/%d:\n", depth,
-		       str_plural(depth), p->comm, task_pid_nr(p));
 	/*
-	 * It's not reliable to print a task's held locks if it's not sleeping
-	 * and it's not the current task.
+	 * Note that it's always somewhat unreliable to print held locks
+	 * of a task that is running on another CPU, but we cannot guarantee
+	 * the stability of ->held_locks without actually stopping all active
+	 * remote CPUs, which we absolutely do not want to do because it's
+	 * very intrusive and thus slow.
+	 *
+	 * So we do the next best thing here: we print out the held lock
+	 * array on a best-effort basis, without crashing even if the
+	 * fields are being modified on another CPU. Note the careful
+	 * construction of print_lock() so that it never crashes.
+	 *
+	 * We also print out the CPU the task is or was last running on, with
+	 * the message saying 'on CPU...' if the task is running, and
+	 * 'last CPU' if it's not.
+	 *
+	 * Also note that the task_is_running(p) information is fundamentally
+	 * racy: even if the message says the task is 'on CPU', the task may
+	 * have scheduled out already, or if it says 'last CPU', it may just
+	 * have scheduled in on another CPU. But even with these limitations
+	 * it's still useful debuggining information.
 	 */
-	if (p != current && task_is_running(p))
-		return;
+	printk("locks held by %s/%d: %d, %s CPU#%d%s\n",
+		p->comm, task_pid_nr(p), depth,
+		task_is_running(p) ? "last" : "on", task_cpu(p),
+		depth > 0 ? ":" : "");
+
 	for (i = 0; i < depth; i++) {
 		printk(" #%d: ", i);
 		print_lock(p->held_locks + i);
@@ -5437,6 +5453,8 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
 			      lock->wait_type_outer,
 			      lock->lock_type);
 	class = register_lock_class(lock, subclass, 0);
+	if (!class)
+		return 0;
 	hlock->class_idx = class - lock_classes;
 
 	curr->lockdep_depth = i;