linux-kernel - Re: [RFC][PATCH 06/13] percpu-rwsem: Provide percpu_down_read

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Date:	Tue, 23 Jun 2015 01:08:32 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	paulmck@...ux.vnet.ibm.com, tj@...nel.org, mingo@...hat.com,
	linux-kernel@...r.kernel.org, der.herr@...r.at, dave@...olabs.net,
	riel@...hat.com, viro@...IV.linux.org.uk,
	torvalds@...ux-foundation.org
Subject: Re: [RFC][PATCH 06/13] percpu-rwsem: Provide
	percpu_down_read_trylock()

On 06/22, Peter Zijlstra wrote:
>
> +static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
> +{
> +	bool ret = true;
> +
> +	preempt_disable();
> +	__this_cpu_inc(*sem->refcount);
> +	if (unlikely(!rcu_sync_is_idle(&sem->rss)))
> +		ret = __percpu_down_read_trylock(sem);
> +	preempt_enable();
> +
> +	if (ret)
> +		rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 1, _RET_IP_);
> +
> +	return ret;
> +}
...
> +bool __percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
> +{
> +	smp_mb(); /* A matches D */
> +
> +	if (likely(smp_load_acquire(&sem->state) != readers_block))
> +		return true;
> +
> +	__percpu_up_read(sem);
> +
> +	return false;
> +}

Looks like we can slightly refactor this code to avoid the code
duplication. But this is minor too and we can do this later.

Reviewed-by: Oleg Nesterov <oleg@...hat.com>

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