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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com,
	bobby.prani@gmail.com, Chris Metcalf <cmetcalf@ezchip.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH v2 tip/core/rcu 8/8] Documentation/memory-barriers.txt: Fix ACCESS_ONCE thinko
Date: Wed,  9 Dec 2015 15:15:02 -0800	[thread overview]
Message-ID: <1449702902-2520-8-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <20151209231426.GA2241@linux.vnet.ibm.com>

From: Chris Metcalf <cmetcalf@ezchip.com>

In commit 2ecf810121c7 ("Documentation/memory-barriers.txt: Add
needed ACCESS_ONCE() calls to memory-barriers.txt") the statement
"Q = P" was converted to "ACCESS_ONCE(Q) = P".  This should have
been "Q = ACCESS_ONCE(P)".  It later became "WRITE_ONCE(Q, P)".
This doesn't match the following text, which is "Q = LOAD P".
Change the statement to be "Q = READ_ONCE(P)".

Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 Documentation/memory-barriers.txt | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index aef9487303d0..85304ebd187c 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -194,7 +194,7 @@ There are some minimal guarantees that may be expected of a CPU:
  (*) On any given CPU, dependent memory accesses will be issued in order, with
      respect to itself.  This means that for:
 
-	WRITE_ONCE(Q, P); smp_read_barrier_depends(); D = READ_ONCE(*Q);
+	Q = READ_ONCE(P); smp_read_barrier_depends(); D = READ_ONCE(*Q);
 
      the CPU will issue the following memory operations:
 
@@ -202,9 +202,9 @@ There are some minimal guarantees that may be expected of a CPU:
 
      and always in that order.  On most systems, smp_read_barrier_depends()
      does nothing, but it is required for DEC Alpha.  The READ_ONCE()
-     and WRITE_ONCE() are required to prevent compiler mischief.  Please
-     note that you should normally use something like rcu_dereference()
-     instead of open-coding smp_read_barrier_depends().
+     is required to prevent compiler mischief.  Please note that you
+     should normally use something like rcu_dereference() instead of
+     open-coding smp_read_barrier_depends().
 
  (*) Overlapping loads and stores within a particular CPU will appear to be
      ordered within that CPU.  This means that for:
-- 
2.5.2


      parent reply	other threads:[~2015-12-09 23:15 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-12-09 23:14 [PATCH v2 tip/core/rcu 0/8] Documentation updates for 4.5 Paul E. McKenney
2015-12-09 23:14 ` [PATCH v2 tip/core/rcu 1/8] documentation: Record RCU requirements Paul E. McKenney
2015-12-09 23:14 ` [PATCH v2 tip/core/rcu 2/8] Documentation: Record bottom-bit-zero guarantee for ->next Paul E. McKenney
2015-12-09 23:14 ` [PATCH v2 tip/core/rcu 3/8] documentation: Cover requirements controlling stall warnings Paul E. McKenney
2015-12-09 23:14 ` [PATCH v2 tip/core/rcu 4/8] documentation: Composability analogies Paul E. McKenney
2015-12-09 23:14 ` [PATCH v2 tip/core/rcu 5/8] documentation: Expand on scheduler/RCU deadlock requirements Paul E. McKenney
2015-12-09 23:15 ` [PATCH v2 tip/core/rcu 6/8] documentation: Clarify RCU memory barriers and requirements Paul E. McKenney
2015-12-09 23:15 ` [PATCH v2 tip/core/rcu 7/8] documentation: Update RCU requirements based on expedited changes Paul E. McKenney
2015-12-09 23:15 ` Paul E. McKenney [this message]

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