linux-kernel - [PATCH tip/core/rcu 02/13] notifiers: Apply rcu_access

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Message-Id: <1380072916-31557-2-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Tue, 24 Sep 2013 18:35:05 -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,
	sbw@....edu, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 02/13] notifiers: Apply rcu_access_pointer() to avoid sparse false positive

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

The sparse checking for rcu_assign_pointer() was recently upgraded
to reject non-__kernel address spaces.  This also rejects __rcu,
which is almost always the right thing to do.  However, the use in
notifier_chain_unregister() is legitimate: It is deleting an element
from an RCU-protected list, and all elements of this list are already
visible to caller.

This commit therefore silences this false positive by laundering the
pointer using rcu_access_pointer() as suggested by Josh Triplett.

Reported-by: kbuild test robot <fengguang.wu@...el.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/notifier.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/notifier.c b/kernel/notifier.c
index 2d5cc4c..1857c71 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -51,7 +51,7 @@ static int notifier_chain_unregister(struct notifier_block **nl,
 {
 	while ((*nl) != NULL) {
 		if ((*nl) == n) {
-			rcu_assign_pointer(*nl, n->next);
+			rcu_assign_pointer(*nl, rcu_access_pointer(n->next));
 			return 0;
 		}
 		nl = &((*nl)->next);
-- 
1.8.1.5

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