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 <[email protected]> --- 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
