linux-kernel - Re: [PATCH tip/core/rcu 10/13] rcu: Add rcu_pointer

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Message-ID: <20151006202741.GW3604@twins.programming.kicks-ass.net>
Date:	Tue, 6 Oct 2015 22:27:41 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	jiangshanlai@...il.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH tip/core/rcu 10/13] rcu: Add rcu_pointer_handoff()

On Tue, Oct 06, 2015 at 09:13:45AM -0700, Paul E. McKenney wrote:
>  /**
> + * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
> + * @p: The pointer to hand off
> + *
> + * This is simply an identity function, but it documents where a pointer
> + * is handed off from RCU to some other synchronization mechanism, for
> + * example, reference counting or locking.  In C11, it would map to
> + * kill_dependency().  It could be used as follows:
> + *
> + *	rcu_read_lock();
> + *	p = rcu_dereference(gp);
> + *	long_lived = is_long_lived(p);
> + *	if (long_lived) {
> + *		if (!atomic_inc_not_zero(p->refcnt))
> + *			long_lived = false;
> + *		else
> + *			p = rcu_pointer_handoff(p);
> + *	}
> + *	rcu_read_unlock();
> + */
> +#define rcu_pointer_handoff(p) (p)

Will you actually be using this? It seems a tad pointless to add if you
don't.
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