linux-kernel - [PATCH tip/core/rcu 08/14] documentation: Add alternative release-acquire outcome

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Message-Id: <1456290047-16654-8-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Tue, 23 Feb 2016 21:00:41 -0800
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 08/14] documentation:  Add alternative release-acquire outcome

The memory-barriers.txt discussion of local transitivity and
release-acquire chains leaves out discussion of the outcome of
the read from "u".  This commit therefore adds an outcome showing
that you can get a "1" from this read even if the release-acquire
pairs don't line up.

Reported-by: Will Deacon <will.deacon@....com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 Documentation/memory-barriers.txt | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index ae9d306725ba..57e4a4b053c5 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1372,6 +1372,10 @@ is possible:
 
 	r0 == 0 && r1 == 1 && r2 == 1 && r3 == 0 && r4 == 0
 
+As an aside, the following outcome is also possible:
+
+	r0 == 0 && r1 == 1 && r2 == 1 && r3 == 0 && r4 == 0 && r5 == 1
+
 Although cpu0(), cpu1(), and cpu2() will see their respective reads and
 writes in order, CPUs not involved in the release-acquire chain might
 well disagree on the order.  This disagreement stems from the fact that
-- 
2.5.2