linux-kernel - Re: [PATCH tip/core/rcu 9/9] rcu: Provide counterpart to rcu

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Date:	Wed, 29 Oct 2014 11:57:04 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.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 9/9] rcu: Provide counterpart to
 rcu_dereference() for non-RCU situations

On Tue, Oct 28, 2014 at 03:10:02PM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> 
> Although rcu_dereference() and friends can be used in situations where
> object lifetimes are being managed by something other than RCU, the
> resulting sparse and lockdep-RCU noise can be annoying.  This commit
> therefore supplies a lockless_dereference(), which provides the
> protection for dereferences without the RCU-related debugging noise.
> 
> Reported-by: Al Viro <viro@...IV.linux.org.uk>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---

> +#define lockless_dereference(p) \
> +({ \
> +	typeof(p) _________p1 = ACCESS_ONCE(p); \
> +	smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
> +	(_________p1); \
> +})

Should we not have at least a single user along with this?
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