Commit 3cfe2e8b authored Apr 26, 2016 by Will Deacon Committed by Ingo Molnar Apr 28, 2016

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>

parent 8d4840e8

Documentation/memory-barriers.txt

+5 −0

Original line number	Diff line number	Diff line
		@@ -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