linux-kernel - [PATCH tip/core/rcu 14/19] rcu: Document RCU_INIT

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Message-Id: <1398729392-15087-14-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Mon, 28 Apr 2014 16:56:27 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	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,
	oleg@...hat.com, sbw@....edu,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 14/19] rcu: Document RCU_INIT_POINTER()'s lack of ordering guarantees

From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>

Although rcu_assign_pointer() provides ordering guarantees,
RCU_INIT_POINTER() does not.  This commit makes that explicit
in the docbook comment header.

Reported-by: Lai Jiangshan <laijs@...fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 include/linux/rcupdate.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index fdc422f3d61d..3c5ef02ea580 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -949,6 +949,9 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  * pointers, but you must use rcu_assign_pointer() to initialize the
  * external-to-structure pointer -after- you have completely initialized
  * the reader-accessible portions of the linked structure.
+ *
+ * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
+ * ordering guarantees for either the CPU or the compiler.
  */
 #define RCU_INIT_POINTER(p, v) \
 	do { \
-- 
1.8.1.5

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