On Thu, Mar 26, 2026 at 03:10:02PM +0000, Dmitry Ilvokhin wrote: > 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 some lock types, the > tracepoint fires after the release but before the wake. Making the > placement consistent across all lock types is not worth the added > complexity. > > For reader/writer locks, the tracepoint fires for every reader releasing > while a writer is waiting, not only for the last reader. > > Signed-off-by: Dmitry Ilvokhin <[email protected]>
Looks plausible: Acked-by: Paul E. McKenney <[email protected]> > --- > include/trace/events/lock.h | 17 +++++++++++++++++ > kernel/locking/mutex.c | 4 ++++ > kernel/locking/percpu-rwsem.c | 11 +++++++++++ > kernel/locking/rtmutex.c | 1 + > kernel/locking/rwbase_rt.c | 6 ++++++ > kernel/locking/rwsem.c | 10 ++++++++-- > kernel/locking/semaphore.c | 4 ++++ > 7 files changed, 51 insertions(+), 2 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..6c2c9312eb8f 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); > > @@ -1194,6 +1197,7 @@ EXPORT_SYMBOL(ww_mutex_lock_interruptible); > > EXPORT_TRACEPOINT_SYMBOL_GPL(contention_begin); > EXPORT_TRACEPOINT_SYMBOL_GPL(contention_end); > +EXPORT_TRACEPOINT_SYMBOL_GPL(contended_release); > > /** > * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0 > diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c > index f3ee7a0d6047..46b5903989b8 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 +295,14 @@ EXPORT_SYMBOL_GPL(percpu_up_write); > void __percpu_up_read(struct percpu_rw_semaphore *sem) > { > lockdep_assert_preemption_disabled(); > + /* > + * After percpu_up_write() completes, rcu_sync_is_idle() can still > + * return false during the grace period, forcing readers into this > + * slowpath. Only trace when a writer is actually waiting for > + * readers to drain. > + */ > + if (trace_contended_release_enabled() && rcuwait_active(&sem->writer)) > + 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..74da5601018f 100644 > --- a/kernel/locking/rwbase_rt.c > +++ b/kernel/locking/rwbase_rt.c > @@ -174,6 +174,8 @@ static void __sched __rwbase_read_unlock(struct rwbase_rt > *rwb, > static __always_inline void rwbase_read_unlock(struct rwbase_rt *rwb, > unsigned int state) > { > + if (trace_contended_release_enabled() && rt_mutex_owner(&rwb->rtmutex)) > + trace_contended_release(rwb); > /* > * rwb->readers can only hit 0 when a writer is waiting for the > * active readers to leave the critical section. > @@ -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..602d5fd3c91a 100644 > --- a/kernel/locking/rwsem.c > +++ b/kernel/locking/rwsem.c > @@ -1387,6 +1387,8 @@ static inline void __up_read(struct rw_semaphore *sem) > rwsem_clear_reader_owned(sem); > tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count); > DEBUG_RWSEMS_WARN_ON(tmp < 0, sem); > + if (trace_contended_release_enabled() && (tmp & RWSEM_FLAG_WAITERS)) > + trace_contended_release(sem); > if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) == > RWSEM_FLAG_WAITERS)) { > clear_nonspinnable(sem); > @@ -1413,8 +1415,10 @@ 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 +1441,10 @@ 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..35ac3498dca5 100644 > --- a/kernel/locking/semaphore.c > +++ b/kernel/locking/semaphore.c > @@ -230,6 +230,10 @@ void __sched up(struct semaphore *sem) > sem->count++; > else > __up(sem, &wake_q); > + > + if (trace_contended_release_enabled() && !wake_q_empty(&wake_q)) > + trace_contended_release(sem); > + > raw_spin_unlock_irqrestore(&sem->lock, flags); > if (!wake_q_empty(&wake_q)) > wake_up_q(&wake_q); > -- > 2.52.0 >
