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Date: Sat, 17 Aug 2013 18:25:53 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: linux-kernel@...r.kernel.org Cc: mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, darren@...art.com, fweisbec@...il.com, sbw@....edu, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Subject: [PATCH tip/core/rcu 3/3] doc: Fix memory-barrier control-dependency example From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Each control-dependency example needs its barriers between the "if" condition and the body of the "if" because a control dependency is a dependency induced by a branch. This commit makes the needed adjustment. Reported-by: Yongming Shen <symingz@...il.com> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> --- Documentation/memory-barriers.txt | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index fa5d8a9..c8c42e6 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -531,9 +531,10 @@ dependency barrier to make it work correctly. Consider the following bit of code: q = &a; - if (p) + if (p) { + <data dependency barrier> q = &b; - <data dependency barrier> + } x = *q; This will not have the desired effect because there is no actual data @@ -542,9 +543,10 @@ attempting to predict the outcome in advance. In such a case what's actually required is: q = &a; - if (p) + if (p) { + <read barrier> q = &b; - <read barrier> + } x = *q; -- 1.8.1.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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