Re: [PATCH RFC 3/3] locking: Wire up contended_release tracepoint

[Steven Rostedt <rostedt@goodmis.org>]

On Wed,  4 Mar 2026 16:56:17 +0000
Dmitry Ilvokhin <d@ilvokhin.com> wrote:

> @@ -204,6 +206,8 @@ static inline void rwbase_write_unlock(struct rwbase_rt *rwb)
>  	unsigned long flags;
>  
>  	raw_spin_lock_irqsave(&rtm->wait_lock, flags);
> +	if (rt_mutex_has_waiters(rtm))
> +		trace_contended_release(rwb);

Hmm, if statements should never be used just for tracepoints without a
static branch. The above should be:

	if (trace_contended_release_enabled() && rt_mutex_has_waiters(rtm))
		trace_contended_release(rwb);

The above "trace_contened_release_enabled()" is a static_branch where it
turns the if statement into a nop when the tracepoint is not enabled, and a
jmp when it is.


>  	__rwbase_write_unlock(rwb, WRITER_BIAS, flags);
>  }
>  
> @@ -213,6 +217,8 @@ static inline void rwbase_write_downgrade(struct rwbase_rt *rwb)
>  	unsigned long flags;
>  
>  	raw_spin_lock_irqsave(&rtm->wait_lock, flags);
> +	if (rt_mutex_has_waiters(rtm))
> +		trace_contended_release(rwb);

Same here.

-- Steve

>  	/* 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 24df4d98f7d2..4e61dc0bb045 100644
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -1360,6 +1360,7 @@ 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();
> @@ -1383,8 +1384,10 @@ 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();
>  }
>  
> @@ -1407,8 +1410,10 @@ 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 3ef032e22f7e..3cef5ba88f7e 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);
>