Date: Wed, 29 Oct 2014 05:42:03 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com,
        dipankar@in.ibm.com, akpm@linux-foundation.org,
        mathieu.desnoyers@efficios.com, josh@joshtriplett.org,
        tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com,
        edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com,
        oleg@redhat.com, bobby.prani@gmail.com
Subject: Re: [PATCH tip/core/rcu 9/9] rcu: Provide counterpart to
 rcu_dereference() for non-RCU situations
Message-ID: <20141029124203.GK5718@linux.vnet.ibm.com>
Reply-To: paulmck@linux.vnet.ibm.com
References: <20141028220944.GA26114@linux.vnet.ibm.com>
 <1414534202-27312-1-git-send-email-paulmck@linux.vnet.ibm.com>
 <1414534202-27312-9-git-send-email-paulmck@linux.vnet.ibm.com>
 <20141029105704.GY3337@twins.programming.kicks-ass.net>
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On Wed, Oct 29, 2014 at 11:57:04AM +0100, Peter Zijlstra wrote:
> On Tue, Oct 28, 2014 at 03:10:02PM -0700, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paulmck@linux.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@ZenIV.linux.org.uk>
> > Signed-off-by: Paul E. McKenney <paulmck@linux.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?

And we do.  In fact, Al Viro has pulled this into his vfs.git tree and
so I will be dropping this patch in favor of his.

							Thanx, Paul

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