linux-kernel - [PATCH] documentation: ACQUIRE applies to loads, RELEASE applies to stores

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Date:	Fri, 22 Apr 2016 11:41:49 +0100
From:	Will Deacon <will.deacon@....com>
To:	linux-kernel@...r.kernel.org
Cc:	Will Deacon <will.deacon@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH] documentation: ACQUIRE applies to loads, RELEASE applies to stores

For compound atomics performing both a load and a store operation, make
it clear that _acquire and _release variants refer only to the load and
store portions of compound atomic. For example, xchg_acquire is an xchg
operation where the load takes on ACQUIRE semantics.

Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Will Deacon <will.deacon@....com>
---
 Documentation/memory-barriers.txt | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index 3729cbe60e41..05f8011011be 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -464,6 +464,11 @@ And a couple of implicit varieties:
      This means that ACQUIRE acts as a minimal "acquire" operation and
      RELEASE acts as a minimal "release" operation.
 
+A subset of the atomic operations described in atomic_ops.txt have ACQUIRE
+and RELEASE variants in addition to fully-ordered and relaxed (no barrier
+semantics) definitions.  For compound atomics performing both a load and a
+store, ACQUIRE semantics apply only to the load and RELEASE semantics apply
+only to the store portion of the operation.
 
 Memory barriers are only required where there's a possibility of interaction
 between two CPUs or between a CPU and a device.  If it can be guaranteed that
-- 
2.1.4