Re: [PATCH v4 3/5] locking: Add contended_release tracepoint to sleepable locks

[Usama Arif <usama.arif@linux.dev>]

On Thu, 26 Mar 2026 15:10:02 +0000 Dmitry Ilvokhin <d@ilvokhin.com> 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 <d@ilvokhin.com>
> ---
>  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);
> +

This won't compile? waiter is declared in the if block, so you are using
it outside scope here.