Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754578Ab3JKXRp (ORCPT ); Fri, 11 Oct 2013 19:17:45 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:45794 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754220Ab3JKXRm (ORCPT ); Fri, 11 Oct 2013 19:17:42 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, "Paul E. McKenney" Subject: [PATCH v3 tip/core/rcu 02/14] notifiers: Apply ACCESS_ONCE() to avoid sparse false positive Date: Fri, 11 Oct 2013 16:17:19 -0700 Message-Id: <1381533451-29018-2-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1381533451-29018-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20131011231659.GA28062@linux.vnet.ibm.com> <1381533451-29018-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13101123-0928-0000-0000-00000277C7E7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1457 Lines: 41 From: "Paul E. McKenney" 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 ACCESS_ONCE() as suggested by Eric Dumazet and Josh Triplett. Reported-by: kbuild test robot Signed-off-by: Paul E. McKenney --- kernel/notifier.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/notifier.c b/kernel/notifier.c index 2d5cc4ccff7f..197eb70805a4 100644 --- a/kernel/notifier.c +++ b/kernel/notifier.c @@ -51,7 +51,8 @@ static int notifier_chain_unregister(struct notifier_block **nl, { while ((*nl) != NULL) { if ((*nl) == n) { - rcu_assign_pointer(*nl, n->next); + /* Both --rcu and visible, so ACCESS_ONCE() is OK. */ + ACCESS_ONCE(*nl) = n->next; return 0; } nl = &((*nl)->next); -- 1.8.1.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/