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Subject: Re: [PATCH v3] rwsem: Support optimistic spinning
From: Tim Chen <tim.c.chen@linux.intel.com>
To: Davidlohr Bueso <davidlohr@hp.com>
Cc: Ingo Molnar <mingo@kernel.org>, Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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Date: Thu, 01 May 2014 09:39:16 -0700
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On Wed, 2014-04-30 at 20:21 -0700, Davidlohr Bueso wrote:

> +
> +static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
> +{
> +	struct task_struct *owner;
> +	bool on_cpu = true;
> +
> +	if (need_resched())
> +		return 0;
> +
> +	rcu_read_lock();
> +	owner = ACCESS_ONCE(sem->owner);
> +	if (owner)
> +		on_cpu = owner->on_cpu;
> +	rcu_read_unlock();
> +
> +	/*
> +	 * If lock->owner is not set, the mutex owner may have
> +	 * just acquired it and not set the owner yet or the mutex

Nitpick. Change the above 2 mutex in comment to rwsem.

> +	 * has been released.
> +	 */
> +	return on_cpu;
> +}
> +

Tim