linux-kernel - Re: [PATCH] locking/percpu_rwsem: Rewrite to not use rwsem

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Date:   Mon, 5 Aug 2019 22:43:18 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Oleg Nesterov <oleg@...hat.com>, Will Deacon <will@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, bigeasy@...utronix.de,
        juri.lelli@...hat.com, williams@...hat.com, bristot@...hat.com,
        longman@...hat.com, dave@...olabs.net, jack@...e.com
Subject: Re: [PATCH] locking/percpu_rwsem: Rewrite to not use rwsem

On Mon, Aug 05, 2019 at 04:02:41PM +0200, Peter Zijlstra wrote:
[...]
>  
>  static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
>  {
> +	rwsem_release(&sem->dep_map, 1, _RET_IP_);
> +
>  	preempt_disable();
>  	/*
>  	 * Same as in percpu_down_read().
>  	 */
> -	if (likely(rcu_sync_is_idle(&sem->rss)))
> +	if (likely(rcu_sync_is_idle(&sem->rss))) {
>  		__this_cpu_dec(*sem->read_count);
> -	else
> -		__percpu_up_read(sem); /* Unconditional memory barrier */
> -	preempt_enable();
> +		preempt_enable();
> +		return;
> +	}
>  
> -	rwsem_release(&sem->rw_sem.dep_map, 1, _RET_IP_);

Missing a preempt_enable() here?

Regards,
Boqun

> +	__percpu_up_read(sem); /* Unconditional memory barrier */
>  }
>  
[...]

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