linux-kernel - Re: [RFC PATCH v3 1/1] mmap_lock: add tracepoints around mmap

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Date:   Fri, 19 Jun 2020 10:30:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Michel Lespinasse <walken@...gle.com>,
        David Howells <dhowells@...hat.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Jonathan Adams <jwadams@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Ying Han <yinghan@...gle.com>
Subject: Re: [RFC PATCH v3 1/1] mmap_lock: add tracepoints around mmap_lock
 acquisition

On Thu, Jun 18, 2020 at 03:22:25PM -0700, Axel Rasmussen wrote:
> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
> index f11b9bd3431d..6aabea1cbc5d 100644
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -1495,6 +1495,20 @@ void __sched down_read(struct rw_semaphore *sem)
>  }
>  EXPORT_SYMBOL(down_read);
> 
> +/*
> + * lock for reading
> + */
> +void __sched down_read_contended_hook(struct rw_semaphore *sem,
> +				      void (*pre)(void *),
> +				      void (*post)(void *), void *arg)
> +{
> +	might_sleep();
> +	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
> +	LOCK_CONTENDED_HOOK(sem, __down_read_trylock, __down_read, pre, post,
> +			    arg);
> +}
> +EXPORT_SYMBOL(down_read_contended_hook);
> +
>  int __sched down_read_killable(struct rw_semaphore *sem)
>  {
>  	might_sleep();
> @@ -1509,6 +1523,24 @@ int __sched down_read_killable(struct rw_semaphore *sem)
>  }
>  EXPORT_SYMBOL(down_read_killable);
> 
> +int __sched down_read_killable_contended_hook(struct rw_semaphore *sem,
> +					      void (*pre)(void *),
> +					      void (*post)(void *, int),
> +					      void *arg)
> +{
> +	might_sleep();
> +	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
> +
> +	if (LOCK_CONTENDED_HOOK_RETURN(sem, __down_read_trylock,
> +				       __down_read_killable, pre, post, arg)) {
> +		rwsem_release(&sem->dep_map, _RET_IP_);
> +		return -EINTR;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(down_read_killable_contended_hook);
> +
>  /*
>   * trylock for reading -- returns 1 if successful, 0 if contention
>   */
> @@ -1533,6 +1565,20 @@ void __sched down_write(struct rw_semaphore *sem)
>  }
>  EXPORT_SYMBOL(down_write);
> 
> +/*
> + * lock for writing
> + */
> +void __sched down_write_contended_hook(struct rw_semaphore *sem,
> +				       void (*pre)(void *),
> +				       void (*post)(void *), void *arg)
> +{
> +	might_sleep();
> +	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
> +	LOCK_CONTENDED_HOOK(sem, __down_write_trylock, __down_write, pre, post,
> +			    arg);
> +}
> +EXPORT_SYMBOL(down_write_contended_hook);
> +
>  /*
>   * lock for writing
>   */
> @@ -1551,6 +1597,24 @@ int __sched down_write_killable(struct rw_semaphore *sem)
>  }
>  EXPORT_SYMBOL(down_write_killable);
> 
> +int __sched down_write_killable_contended_hook(struct rw_semaphore *sem,
> +					       void (*pre)(void *),
> +					       void (*post)(void *, int),
> +					       void *arg)
> +{
> +	might_sleep();
> +	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
> +
> +	if (LOCK_CONTENDED_HOOK_RETURN(sem, __down_write_trylock,
> +				       __down_write_killable, pre, post, arg)) {
> +		rwsem_release(&sem->dep_map, _RET_IP_);
> +		return -EINTR;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(down_write_killable_contended_hook);
> +
>  /*
>   * trylock for writing -- returns 1 if successful, 0 if contention
>   */

NAK, absolutely not going to happen. This is an atrocious API to expose,
worse you're exporting.