linux-kernel - Re: [PATCH] locking/rwsem: Add up_write_non_owner() for percpu_up

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Date:   Mon, 9 Apr 2018 13:20:13 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        "Theodore Y. Ts'o" <tytso@....edu>
Subject: Re: [PATCH] locking/rwsem: Add up_write_non_owner() for
 percpu_up_write()

On 04/04, Waiman Long wrote:
>
> --- a/kernel/locking/percpu-rwsem.c
> +++ b/kernel/locking/percpu-rwsem.c
> @@ -179,8 +179,10 @@ void percpu_up_write(struct percpu_rw_semaphore *sem)
>  
>  	/*
>  	 * Release the write lock, this will allow readers back in the game.
> +	 * percpu_up_write() may be called from a task different from the one
> +	 * taking the lock.
>  	 */
> -	up_write(&sem->rw_sem);
> +	up_write_non_owner(&sem->rw_sem);
>  
>  	/*
>  	 * Once this completes (at least one RCU-sched grace period hence) the
> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
> index 30465a2..140d5ef 100644
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -222,4 +222,17 @@ void up_read_non_owner(struct rw_semaphore *sem)
>  
>  #endif
>  
> +#ifdef CONFIG_DEBUG_RWSEMS
> +/*
> + * release a write lock from a different task
> + */
> +void up_write_non_owner(struct rw_semaphore *sem)
> +{
> +	rwsem_release(&sem->dep_map, 1, _RET_IP_);
> +	DEBUG_RWSEMS_WARN_ON(!sem->owner || (sem->owner == RWSEM_READER_OWNED));
>  
> +	rwsem_clear_owner(sem);
> +	__up_write(sem);
> +}

Hmm. Can you look at lockdep_sb_freeze_release() and lockdep_sb_freeze_acquire()?

At first glance, it would be much better to set sem->owner = current in
percpu_rwsem_acquire(), no?

Oleg.