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authorWill Deacon <will.deacon@arm.com>2016-04-26 10:22:07 -0700
committerIngo Molnar <mingo@kernel.org>2016-04-28 10:57:51 +0200
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locking/Documentation: Clarify that 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. Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: corbet@lwn.net Cc: dave@stgolabs.net Cc: dhowells@redhat.com Cc: linux-doc@vger.kernel.org Link: http://lkml.kernel.org/r/1461691328-5429-3-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index 8b11e54238bf..147ae8ec836f 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -498,6 +498,11 @@ 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