linux-kernel - [PATCH tip/core/rcu 5/5] documentation: Add lockless

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Message-Id: <1444149262-14966-5-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Tue,  6 Oct 2015 09:34:22 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	bobby.prani@...il.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 5/5] documentation: Add lockless_dereference()

The recently added lockless_dereference() macro is not present in the
Documentation/ directory, so this commit fixes that.

Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 Documentation/memory-barriers.txt | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index d336e4d42029..8e7cf9ad3db1 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1710,6 +1710,17 @@ There are some more advanced barrier functions:
      operations" subsection for information on where to use these.
 
 
+ (*) lockless_dereference();
+     This can be thought of as a pointer-fetch wrapper around the
+     smp_read_barrier_depends() data-dependency barrier.
+
+     This is also similar to rcu_dereference(), but in cases where
+     object lifetime is handled by some mechanism other than RCU, for
+     example, when the objects removed only when the system goes down.
+     In addition, lockless_dereference() is used in some data structures
+     that can be used both with and without RCU.
+
+
  (*) dma_wmb();
  (*) dma_rmb();
 
-- 
2.5.2

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