linux-kernel - [RESEND PATCH] documentation: memory-barriers: fix smp_mb__before

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Message-Id: <1427791181-21952-1-git-send-email-will.deacon@arm.com>
Date:	Tue, 31 Mar 2015 09:39:41 +0100
From:	Will Deacon <will.deacon@....com>
To:	linux-kernel@...r.kernel.org
Cc:	Will Deacon <will.deacon@....com>, Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: [RESEND PATCH] documentation: memory-barriers: fix smp_mb__before_spinlock() semantics

Our current documentation claims that, when followed by an ACQUIRE,
smp_mb__before_spinlock() orders prior loads against subsequent loads
and stores, which isn't actually true.

Fix the documentation to state that this sequence orders only prior
stores against subsequent loads and stores.

Cc: Oleg Nesterov <oleg@...hat.com>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Will Deacon <will.deacon@....com>
---

Could somebody pick this up please? I guess I could route it via the arm64
tree with an Ack, but I'd rather it went through Paul or -tip.

 Documentation/memory-barriers.txt | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index ca2387ef27ab..fa28a0c1e2b1 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1768,10 +1768,9 @@ for each construct.  These operations all imply certain barriers:
 
      Memory operations issued before the ACQUIRE may be completed after
      the ACQUIRE operation has completed.  An smp_mb__before_spinlock(),
-     combined with a following ACQUIRE, orders prior loads against
-     subsequent loads and stores and also orders prior stores against
-     subsequent stores.  Note that this is weaker than smp_mb()!  The
-     smp_mb__before_spinlock() primitive is free on many architectures.
+     combined with a following ACQUIRE, orders prior stores against
+     subsequent loads and stores. Note that this is weaker than smp_mb()!
+     The smp_mb__before_spinlock() primitive is free on many architectures.
 
  (2) RELEASE operation implication:
 
-- 
2.1.4

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