[PATCH v3 0/4] locking: contended_release tracepoint instrumentation

[PATCH v3 0/4] locking: contended_release tracepoint instrumentation

[Dmitry Ilvokhin]

The existing contention_begin/contention_end tracepoints fire on the
waiter side. The lock holder's identity and stack can be captured at
contention_begin time (e.g. perf lock contention --lock-owner), but
this reflects the holder's state when a waiter arrives, not when the
lock is actually released.

This series adds a contended_release tracepoint that fires on the
holder side when a lock with waiters is released. This provides:

- Hold time estimation: when the holder's own acquisition was
  contended, its contention_end (acquisition) and contended_release
  can be correlated to measure how long the lock was held under
  contention.

- The holder's stack at release time, which may differ from what perf lock
  contention --lock-owner captures if the holder does significant work between
  the waiter's arrival and the unlock.

The series is structured as follows:

1. Remove unnecessary linux/sched.h include from trace/events/lock.h.
2. Extract __percpu_up_read() out of the inline percpu_up_read() to
   avoid binary size increase from adding a tracepoint.
3. Add contended_release tracepoint and instrument sleepable locks:
   mutex, rtmutex, semaphore, rwsem, percpu-rwsem, and rwbase_rt.
4. RFC. Extend contended_release to queued spinlocks and queued rwlocks.

v2 -> v3:

- Added new patch: extend contended_release tracepoint to queued spinlocks
  and queued rwlocks (marked as RFC, requesting feedback). This is prompted by
  Matthew Wilcox's suggestion to try to come up with generic instrumentation,
  instead of instrumenting each "special" lock manually. See [1] for the
  discussion.
- Reworked tracepoint placement to fire before the lock is released and
  before the waiter is woken where possible, for consistency with
  spinning locks where there is no explicit wake (inspired by Usama Arif's
  suggestion).
- Remove unnecessary linux/sched.h include from trace/events/lock.h.

RFC -> v2:

- Add trace_contended_release_enabled() guard before waiter checks that
  exist only for the tracepoint (Steven Rostedt).
- Rename __percpu_up_read_slowpath() to __percpu_up_read() (Peter
  Zijlstra).
- Add extern for __percpu_up_read() (Peter Zijlstra).
- Squashed tracepoint introduction and usage commits (Masami Hiramatsu).

v2: https://lore.kernel.org/all/cover.1773164180.git.d@ilvokhin.com/
RFC: https://lore.kernel.org/all/cover.1772642407.git.d@ilvokhin.com/

[1]: https://lore.kernel.org/all/aa7G1nD7Rd9F4eBH@casper.infradead.org/

Dmitry Ilvokhin (4):
  tracing/lock: Remove unnecessary linux/sched.h include
  locking/percpu-rwsem: Extract __percpu_up_read()
  locking: Add contended_release tracepoint to sleepable locks
  locking: Add contended_release tracepoint to spinning locks

 include/asm-generic/qrwlock.h   | 48 +++++++++++++++++++++++++++------
 include/asm-generic/qspinlock.h | 25 +++++++++++++++--
 include/linux/percpu-rwsem.h    | 15 +++--------
 include/trace/events/lock.h     | 18 ++++++++++++-
 kernel/locking/mutex.c          |  3 +++
 kernel/locking/percpu-rwsem.c   | 22 +++++++++++++++
 kernel/locking/qrwlock.c        | 16 +++++++++++
 kernel/locking/qspinlock.c      |  8 ++++++
 kernel/locking/rtmutex.c        |  1 +
 kernel/locking/rwbase_rt.c      |  8 +++++-
 kernel/locking/rwsem.c          |  9 +++++--
 kernel/locking/semaphore.c      |  4 ++-
 12 files changed, 150 insertions(+), 27 deletions(-)

-- 
2.52.0

[PATCH v3 1/4] tracing/lock: Remove unnecessary linux/sched.h include

[Dmitry Ilvokhin]

None of the trace events in lock.h reference anything from
linux/sched.h. Remove the unnecessary include.

Signed-off-by: Dmitry Ilvokhin <d@ilvokhin.com>
---
 include/trace/events/lock.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/include/trace/events/lock.h b/include/trace/events/lock.h
index 8e89baa3775f..da978f2afb45 100644
--- a/include/trace/events/lock.h
+++ b/include/trace/events/lock.h
@@ -5,7 +5,6 @@
 #if !defined(_TRACE_LOCK_H) || defined(TRACE_HEADER_MULTI_READ)
 #define _TRACE_LOCK_H
 
-#include <linux/sched.h>
 #include <linux/tracepoint.h>
 
 /* flags for lock:contention_begin */
-- 
2.52.0

[PATCH v3 2/4] locking/percpu-rwsem: Extract __percpu_up_read()

[Dmitry Ilvokhin]

Move the percpu_up_read() slowpath out of the inline function into a new
__percpu_up_read() to avoid binary size increase from adding a
tracepoint to an inlined function.

Signed-off-by: Dmitry Ilvokhin <d@ilvokhin.com>
Acked-by: Usama Arif <usama.arif@linux.dev>
---
 include/linux/percpu-rwsem.h  | 15 +++------------
 kernel/locking/percpu-rwsem.c | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
index c8cb010d655e..39d5bf8e6562 100644
--- a/include/linux/percpu-rwsem.h
+++ b/include/linux/percpu-rwsem.h
@@ -107,6 +107,8 @@ static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
 	return ret;
 }
 
+extern void __percpu_up_read(struct percpu_rw_semaphore *sem);
+
 static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
 {
 	rwsem_release(&sem->dep_map, _RET_IP_);
@@ -118,18 +120,7 @@ static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
 	if (likely(rcu_sync_is_idle(&sem->rss))) {
 		this_cpu_dec(*sem->read_count);
 	} else {
-		/*
-		 * slowpath; reader will only ever wake a single blocked
-		 * writer.
-		 */
-		smp_mb(); /* B matches C */
-		/*
-		 * In other words, if they see our decrement (presumably to
-		 * aggregate zero, as that is the only time it matters) they
-		 * will also see our critical section.
-		 */
-		this_cpu_dec(*sem->read_count);
-		rcuwait_wake_up(&sem->writer);
+		__percpu_up_read(sem);
 	}
 	preempt_enable();
 }
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index ef234469baac..f3ee7a0d6047 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -288,3 +288,21 @@ void percpu_up_write(struct percpu_rw_semaphore *sem)
 	rcu_sync_exit(&sem->rss);
 }
 EXPORT_SYMBOL_GPL(percpu_up_write);
+
+void __percpu_up_read(struct percpu_rw_semaphore *sem)
+{
+	lockdep_assert_preemption_disabled();
+	/*
+	 * slowpath; reader will only ever wake a single blocked
+	 * writer.
+	 */
+	smp_mb(); /* B matches C */
+	/*
+	 * In other words, if they see our decrement (presumably to
+	 * aggregate zero, as that is the only time it matters) they
+	 * will also see our critical section.
+	 */
+	this_cpu_dec(*sem->read_count);
+	rcuwait_wake_up(&sem->writer);
+}
+EXPORT_SYMBOL_GPL(__percpu_up_read);
-- 
2.52.0

[PATCH v3 3/4] locking: Add contended_release tracepoint to sleepable locks

[Dmitry Ilvokhin]

Add the contended_release trace event. This tracepoint fires on the
holder side when a contended lock is released, complementing the
existing contention_begin/contention_end tracepoints which fire on the
waiter side.

This enables correlating lock hold time under contention with waiter
events by lock address.

Add trace_contended_release() calls to the slowpath unlock paths of
sleepable locks: mutex, rtmutex, semaphore, rwsem, percpu-rwsem, and
RT-specific rwbase locks.

Where possible, trace_contended_release() fires before the lock is
released and before the waiter is woken. For rwsem, semaphore, and
rwbase_rt read unlock, the tracepoint fires after the release but before
the wake, as contention is determined by the return value of the atomic
release operation.

Signed-off-by: Dmitry Ilvokhin <d@ilvokhin.com>
---
 include/trace/events/lock.h   | 17 +++++++++++++++++
 kernel/locking/mutex.c        |  3 +++
 kernel/locking/percpu-rwsem.c |  4 ++++
 kernel/locking/rtmutex.c      |  1 +
 kernel/locking/rwbase_rt.c    |  8 +++++++-
 kernel/locking/rwsem.c        |  9 +++++++--
 kernel/locking/semaphore.c    |  4 +++-
 7 files changed, 42 insertions(+), 4 deletions(-)

diff --git a/include/trace/events/lock.h b/include/trace/events/lock.h
index da978f2afb45..1ded869cd619 100644
--- a/include/trace/events/lock.h
+++ b/include/trace/events/lock.h
@@ -137,6 +137,23 @@ TRACE_EVENT(contention_end,
 	TP_printk("%p (ret=%d)", __entry->lock_addr, __entry->ret)
 );
 
+TRACE_EVENT(contended_release,
+
+	TP_PROTO(void *lock),
+
+	TP_ARGS(lock),
+
+	TP_STRUCT__entry(
+		__field(void *, lock_addr)
+	),
+
+	TP_fast_assign(
+		__entry->lock_addr = lock;
+	),
+
+	TP_printk("%p", __entry->lock_addr)
+);
+
 #endif /* _TRACE_LOCK_H */
 
 /* This part must be outside protection */
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 427187ff02db..bb25741c2768 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -997,6 +997,9 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
 		wake_q_add(&wake_q, next);
 	}
 
+	if (trace_contended_release_enabled() && waiter)
+		trace_contended_release(lock);
+
 	if (owner & MUTEX_FLAG_HANDOFF)
 		__mutex_handoff(lock, next);
 
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index f3ee7a0d6047..6bf2ccddd42d 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -263,6 +263,9 @@ void percpu_up_write(struct percpu_rw_semaphore *sem)
 {
 	rwsem_release(&sem->dep_map, _RET_IP_);
 
+	if (trace_contended_release_enabled() && wq_has_sleeper(&sem->waiters))
+		trace_contended_release(sem);
+
 	/*
 	 * Signal the writer is done, no fast path yet.
 	 *
@@ -292,6 +295,7 @@ EXPORT_SYMBOL_GPL(percpu_up_write);
 void __percpu_up_read(struct percpu_rw_semaphore *sem)
 {
 	lockdep_assert_preemption_disabled();
+	trace_contended_release(sem);
 	/*
 	 * slowpath; reader will only ever wake a single blocked
 	 * writer.
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index ccaba6148b61..3db8a840b4e8 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1466,6 +1466,7 @@ static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock)
 		raw_spin_lock_irqsave(&lock->wait_lock, flags);
 	}
 
+	trace_contended_release(lock);
 	/*
 	 * The wakeup next waiter path does not suffer from the above
 	 * race. See the comments there.
diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c
index 82e078c0665a..081778934b13 100644
--- a/kernel/locking/rwbase_rt.c
+++ b/kernel/locking/rwbase_rt.c
@@ -162,8 +162,10 @@ static void __sched __rwbase_read_unlock(struct rwbase_rt *rwb,
 	 * worst case which can happen is a spurious wakeup.
 	 */
 	owner = rt_mutex_owner(rtm);
-	if (owner)
+	if (owner) {
+		trace_contended_release(rwb);
 		rt_mutex_wake_q_add_task(&wqh, owner, state);
+	}
 
 	/* Pairs with the preempt_enable in rt_mutex_wake_up_q() */
 	preempt_disable();
@@ -205,6 +207,8 @@ static inline void rwbase_write_unlock(struct rwbase_rt *rwb)
 	unsigned long flags;
 
 	raw_spin_lock_irqsave(&rtm->wait_lock, flags);
+	if (trace_contended_release_enabled() && rt_mutex_has_waiters(rtm))
+		trace_contended_release(rwb);
 	__rwbase_write_unlock(rwb, WRITER_BIAS, flags);
 }
 
@@ -214,6 +218,8 @@ static inline void rwbase_write_downgrade(struct rwbase_rt *rwb)
 	unsigned long flags;
 
 	raw_spin_lock_irqsave(&rtm->wait_lock, flags);
+	if (trace_contended_release_enabled() && rt_mutex_has_waiters(rtm))
+		trace_contended_release(rwb);
 	/* Release it and account current as reader */
 	__rwbase_write_unlock(rwb, WRITER_BIAS - 1, flags);
 }
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index bf647097369c..767a1a2b7d8c 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -1390,6 +1390,7 @@ static inline void __up_read(struct rw_semaphore *sem)
 	if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) ==
 		      RWSEM_FLAG_WAITERS)) {
 		clear_nonspinnable(sem);
+		trace_contended_release(sem);
 		rwsem_wake(sem);
 	}
 	preempt_enable();
@@ -1413,8 +1414,10 @@ static inline void __up_write(struct rw_semaphore *sem)
 	preempt_disable();
 	rwsem_clear_owner(sem);
 	tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count);
-	if (unlikely(tmp & RWSEM_FLAG_WAITERS))
+	if (unlikely(tmp & RWSEM_FLAG_WAITERS)) {
+		trace_contended_release(sem);
 		rwsem_wake(sem);
+	}
 	preempt_enable();
 }
 
@@ -1437,8 +1440,10 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
 	tmp = atomic_long_fetch_add_release(
 		-RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count);
 	rwsem_set_reader_owned(sem);
-	if (tmp & RWSEM_FLAG_WAITERS)
+	if (tmp & RWSEM_FLAG_WAITERS) {
+		trace_contended_release(sem);
 		rwsem_downgrade_wake(sem);
+	}
 	preempt_enable();
 }
 
diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c
index 74d41433ba13..d46415095dd6 100644
--- a/kernel/locking/semaphore.c
+++ b/kernel/locking/semaphore.c
@@ -231,8 +231,10 @@ void __sched up(struct semaphore *sem)
 	else
 		__up(sem, &wake_q);
 	raw_spin_unlock_irqrestore(&sem->lock, flags);
-	if (!wake_q_empty(&wake_q))
+	if (!wake_q_empty(&wake_q)) {
+		trace_contended_release(sem);
 		wake_up_q(&wake_q);
+	}
 }
 EXPORT_SYMBOL(up);
 
-- 
2.52.0

[RFC PATCH v3 4/4] locking: Add contended_release tracepoint to spinning locks

[Dmitry Ilvokhin]

Extend the contended_release tracepoint to queued spinlocks and queued
rwlocks.

When the tracepoint is disabled, the only addition to the hot path is a
single NOP instruction (the static branch). When enabled, the contention
check, trace call, and unlock are combined in an out-of-line function to
minimize hot path impact, avoiding the compiler needing to preserve the
lock pointer in a callee-saved register across the trace call.

Binary size impact (x86_64, defconfig):
  uninlined unlock (common case): +983 bytes  (+0.00%)
  inlined unlock (worst case):    +71554 bytes (+0.30%)

The inlined unlock case could not be achieved through Kconfig options on
x86_64 as PREEMPT_BUILD unconditionally selects UNINLINE_SPIN_UNLOCK on
x86_64. The UNINLINE_SPIN_UNLOCK guards were manually inverted to force
inline the unlock path and estimate the worst case binary size increase.

Signed-off-by: Dmitry Ilvokhin <d@ilvokhin.com>
---
 include/asm-generic/qrwlock.h   | 48 +++++++++++++++++++++++++++------
 include/asm-generic/qspinlock.h | 25 +++++++++++++++--
 kernel/locking/qrwlock.c        | 16 +++++++++++
 kernel/locking/qspinlock.c      |  8 ++++++
 4 files changed, 87 insertions(+), 10 deletions(-)

diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
index 75b8f4601b28..e24dc537fd66 100644
--- a/include/asm-generic/qrwlock.h
+++ b/include/asm-generic/qrwlock.h
@@ -14,6 +14,7 @@
 #define __ASM_GENERIC_QRWLOCK_H
 
 #include <linux/atomic.h>
+#include <linux/tracepoint-defs.h>
 #include <asm/barrier.h>
 #include <asm/processor.h>
 
@@ -35,6 +36,10 @@
  */
 extern void queued_read_lock_slowpath(struct qrwlock *lock);
 extern void queued_write_lock_slowpath(struct qrwlock *lock);
+extern void queued_read_unlock_traced(struct qrwlock *lock);
+extern void queued_write_unlock_traced(struct qrwlock *lock);
+
+DECLARE_TRACEPOINT(contended_release);
 
 /**
  * queued_read_trylock - try to acquire read lock of a queued rwlock
@@ -102,10 +107,16 @@ static inline void queued_write_lock(struct qrwlock *lock)
 }
 
 /**
- * queued_read_unlock - release read lock of a queued rwlock
+ * queued_rwlock_is_contended - check if the lock is contended
  * @lock : Pointer to queued rwlock structure
+ * Return: 1 if lock contended, 0 otherwise
  */
-static inline void queued_read_unlock(struct qrwlock *lock)
+static inline int queued_rwlock_is_contended(struct qrwlock *lock)
+{
+	return arch_spin_is_locked(&lock->wait_lock);
+}
+
+static __always_inline void __queued_read_unlock(struct qrwlock *lock)
 {
 	/*
 	 * Atomically decrement the reader count
@@ -114,22 +125,43 @@ static inline void queued_read_unlock(struct qrwlock *lock)
 }
 
 /**
- * queued_write_unlock - release write lock of a queued rwlock
+ * queued_read_unlock - release read lock of a queued rwlock
  * @lock : Pointer to queued rwlock structure
  */
-static inline void queued_write_unlock(struct qrwlock *lock)
+static inline void queued_read_unlock(struct qrwlock *lock)
+{
+	/*
+	 * Trace and unlock are combined in the traced unlock variant so
+	 * the compiler does not need to preserve the lock pointer across
+	 * the function call, avoiding callee-saved register save/restore
+	 * on the hot path.
+	 */
+	if (tracepoint_enabled(contended_release)) {
+		queued_read_unlock_traced(lock);
+		return;
+	}
+
+	__queued_read_unlock(lock);
+}
+
+static __always_inline void __queued_write_unlock(struct qrwlock *lock)
 {
 	smp_store_release(&lock->wlocked, 0);
 }
 
 /**
- * queued_rwlock_is_contended - check if the lock is contended
+ * queued_write_unlock - release write lock of a queued rwlock
  * @lock : Pointer to queued rwlock structure
- * Return: 1 if lock contended, 0 otherwise
  */
-static inline int queued_rwlock_is_contended(struct qrwlock *lock)
+static inline void queued_write_unlock(struct qrwlock *lock)
 {
-	return arch_spin_is_locked(&lock->wait_lock);
+	/* See comment in queued_read_unlock(). */
+	if (tracepoint_enabled(contended_release)) {
+		queued_write_unlock_traced(lock);
+		return;
+	}
+
+	__queued_write_unlock(lock);
 }
 
 /*
diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h
index bf47cca2c375..8ba463a3b891 100644
--- a/include/asm-generic/qspinlock.h
+++ b/include/asm-generic/qspinlock.h
@@ -41,6 +41,7 @@
 
 #include <asm-generic/qspinlock_types.h>
 #include <linux/atomic.h>
+#include <linux/tracepoint-defs.h>
 
 #ifndef queued_spin_is_locked
 /**
@@ -116,6 +117,19 @@ static __always_inline void queued_spin_lock(struct qspinlock *lock)
 #endif
 
 #ifndef queued_spin_unlock
+
+DECLARE_TRACEPOINT(contended_release);
+
+extern void queued_spin_unlock_traced(struct qspinlock *lock);
+
+static __always_inline void __queued_spin_unlock(struct qspinlock *lock)
+{
+	/*
+	 * unlock() needs release semantics:
+	 */
+	smp_store_release(&lock->locked, 0);
+}
+
 /**
  * queued_spin_unlock - release a queued spinlock
  * @lock : Pointer to queued spinlock structure
@@ -123,9 +137,16 @@ static __always_inline void queued_spin_lock(struct qspinlock *lock)
 static __always_inline void queued_spin_unlock(struct qspinlock *lock)
 {
 	/*
-	 * unlock() needs release semantics:
+	 * Trace and unlock are combined in queued_spin_unlock_traced()
+	 * so the compiler does not need to preserve the lock pointer
+	 * across the function call, avoiding callee-saved register
+	 * save/restore on the hot path.
 	 */
-	smp_store_release(&lock->locked, 0);
+	if (tracepoint_enabled(contended_release)) {
+		queued_spin_unlock_traced(lock);
+		return;
+	}
+	__queued_spin_unlock(lock);
 }
 #endif
 
diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
index d2ef312a8611..5f7a0fc2b27a 100644
--- a/kernel/locking/qrwlock.c
+++ b/kernel/locking/qrwlock.c
@@ -90,3 +90,19 @@ void __lockfunc queued_write_lock_slowpath(struct qrwlock *lock)
 	trace_contention_end(lock, 0);
 }
 EXPORT_SYMBOL(queued_write_lock_slowpath);
+
+void __lockfunc queued_read_unlock_traced(struct qrwlock *lock)
+{
+	if (queued_rwlock_is_contended(lock))
+		trace_contended_release(lock);
+	__queued_read_unlock(lock);
+}
+EXPORT_SYMBOL(queued_read_unlock_traced);
+
+void __lockfunc queued_write_unlock_traced(struct qrwlock *lock)
+{
+	if (queued_rwlock_is_contended(lock))
+		trace_contended_release(lock);
+	__queued_write_unlock(lock);
+}
+EXPORT_SYMBOL(queued_write_unlock_traced);
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index af8d122bb649..1544dcec65fa 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -104,6 +104,14 @@ static __always_inline u32  __pv_wait_head_or_lock(struct qspinlock *lock,
 #define queued_spin_lock_slowpath	native_queued_spin_lock_slowpath
 #endif
 
+void __lockfunc queued_spin_unlock_traced(struct qspinlock *lock)
+{
+	if (queued_spin_is_contended(lock))
+		trace_contended_release(lock);
+	__queued_spin_unlock(lock);
+}
+EXPORT_SYMBOL(queued_spin_unlock_traced);
+
 #endif /* _GEN_PV_LOCK_SLOWPATH */
 
 /**
-- 
2.52.0

Re: [PATCH v3 0/4] locking: contended_release tracepoint instrumentation

[Andrew Morton]

On Wed, 18 Mar 2026 18:45:17 +0000 Dmitry Ilvokhin <d@ilvokhin.com> wrote:

> The existing contention_begin/contention_end tracepoints fire on the
> waiter side. The lock holder's identity and stack can be captured at
> contention_begin time (e.g. perf lock contention --lock-owner), but
> this reflects the holder's state when a waiter arrives, not when the
> lock is actually released.
> 
> This series adds a contended_release tracepoint that fires on the
> holder side when a lock with waiters is released. This provides:
> 
> - Hold time estimation: when the holder's own acquisition was
>   contended, its contention_end (acquisition) and contended_release
>   can be correlated to measure how long the lock was held under
>   contention.
> 
> - The holder's stack at release time, which may differ from what perf lock
>   contention --lock-owner captures if the holder does significant work between
>   the waiter's arrival and the unlock.
> 
> The series is structured as follows:
> 
> 1. Remove unnecessary linux/sched.h include from trace/events/lock.h.
> 2. Extract __percpu_up_read() out of the inline percpu_up_read() to
>    avoid binary size increase from adding a tracepoint.
> 3. Add contended_release tracepoint and instrument sleepable locks:
>    mutex, rtmutex, semaphore, rwsem, percpu-rwsem, and rwbase_rt.

AI review:
	https://sashiko.dev/#/patchset/cover.1773858853.git.d@ilvokhin.com

Re: [PATCH v3 0/4] locking: contended_release tracepoint instrumentation

[Dmitry Ilvokhin]

On Sat, Mar 21, 2026 at 05:10:02PM -0700, Andrew Morton wrote:
> On Wed, 18 Mar 2026 18:45:17 +0000 Dmitry Ilvokhin <d@ilvokhin.com> wrote:
> 
> > The existing contention_begin/contention_end tracepoints fire on the
> > waiter side. The lock holder's identity and stack can be captured at
> > contention_begin time (e.g. perf lock contention --lock-owner), but
> > this reflects the holder's state when a waiter arrives, not when the
> > lock is actually released.
> > 
> > This series adds a contended_release tracepoint that fires on the
> > holder side when a lock with waiters is released. This provides:
> > 
> > - Hold time estimation: when the holder's own acquisition was
> >   contended, its contention_end (acquisition) and contended_release
> >   can be correlated to measure how long the lock was held under
> >   contention.
> > 
> > - The holder's stack at release time, which may differ from what perf lock
> >   contention --lock-owner captures if the holder does significant work between
> >   the waiter's arrival and the unlock.
> > 
> > The series is structured as follows:
> > 
> > 1. Remove unnecessary linux/sched.h include from trace/events/lock.h.
> > 2. Extract __percpu_up_read() out of the inline percpu_up_read() to
> >    avoid binary size increase from adding a tracepoint.
> > 3. Add contended_release tracepoint and instrument sleepable locks:
> >    mutex, rtmutex, semaphore, rwsem, percpu-rwsem, and rwbase_rt.
> 
> AI review:
> 	https://sashiko.dev/#/patchset/cover.1773858853.git.d@ilvokhin.com

Thanks, Andrew, appreciate you sharing the link.

The AI review looks reasonable. I'll go through it and address the
feedback in the next revision. The kernel test robot is also reporting
failures on some configs, which seem related to the Sashiko comments.