From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753967Ab3KPAYW (ORCPT ); Fri, 15 Nov 2013 19:24:22 -0500 Received: from e31.co.us.ibm.com ([32.97.110.149]:43716 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753865Ab3KPAX4 (ORCPT ); Fri, 15 Nov 2013 19:23:56 -0500 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, "Michael S. Tsirkin" , "Paul E. McKenney" Subject: [PATCH tip/core/rcu 12/16] srcu: Add API for barrier after srcu_read_unlock() Date: Fri, 15 Nov 2013 16:23:34 -0800 Message-Id: <1384561418-30575-12-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1384561418-30575-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20131116002316.GA29049@linux.vnet.ibm.com> <1384561418-30575-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13111600-8236-0000-0000-000003D80E55 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Michael S. Tsirkin" The srcu_read_unlock() implementation currently contains a full memory barrier, but that has not always been the case and it someday again might not be the case. However, given that the memory barrier is there, it is useful to be able to rely on it. This commit therefore adds a new smp_mb__after_srcu_read_unlock() API that, together with a preceding srcu_read_unlock(), is guaranteed to provide a full barrier. Signed-off-by: Michael S. Tsirkin Acked-by: "Lai Jiangshan" Signed-off-by: Paul E. McKenney --- include/linux/srcu.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/include/linux/srcu.h b/include/linux/srcu.h index c114614ed172..9b058eecd403 100644 --- a/include/linux/srcu.h +++ b/include/linux/srcu.h @@ -237,4 +237,18 @@ static inline void srcu_read_unlock(struct srcu_struct *sp, int idx) __srcu_read_unlock(sp, idx); } +/** + * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock + * + * Converts the preceding srcu_read_unlock into a two-way memory barrier. + * + * Call this after srcu_read_unlock, to guarantee that all memory operations + * that occur after smp_mb__after_srcu_read_unlock will appear to happen after + * the preceding srcu_read_unlock. + */ +static inline void smp_mb__after_srcu_read_unlock(void) +{ + /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */ +} + #endif -- 1.8.1.5