From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759962AbbIDNWh (ORCPT ); Fri, 4 Sep 2015 09:22:37 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:50319 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933030AbbIDNKK (ORCPT ); Fri, 4 Sep 2015 09:10:10 -0400 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: "Paul E. McKenney" , Al Viro , Luis Henriques Subject: [PATCH 3.16.y-ckt 097/130] rcu: Provide counterpart to rcu_dereference() for non-RCU situations Date: Fri, 4 Sep 2015 14:08:05 +0100 Message-Id: <1441372118-5933-98-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1441372118-5933-1-git-send-email-luis.henriques@canonical.com> References: <1441372118-5933-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.16 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.7-ckt17 -stable review patch. If anyone has any objections, please let me know. ------------------ From: "Paul E. McKenney" commit 54ef6df3f3f1353d99c80c437259d317b2cd1cbd upstream. Although rcu_dereference() and friends can be used in situations where object lifetimes are being managed by something other than RCU, the resulting sparse and lockdep-RCU noise can be annoying. This commit therefore supplies a lockless_dereference(), which provides the protection for dereferences without the RCU-related debugging noise. Reported-by: Al Viro Signed-off-by: Paul E. McKenney Signed-off-by: Al Viro [ luis: 3.16 prereq for: 37868fe113ff "x86/ldt: Make modify_ldt synchronous" ] Signed-off-by: Luis Henriques --- include/linux/rcupdate.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 6a94cc8b1ca0..53ea8bed34bc 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -593,6 +593,21 @@ static inline void rcu_preempt_sleep_check(void) #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v) /** + * lockless_dereference() - safely load a pointer for later dereference + * @p: The pointer to load + * + * Similar to rcu_dereference(), but for situations where the pointed-to + * object's lifetime is managed by something other than RCU. That + * "something other" might be reference counting or simple immortality. + */ +#define lockless_dereference(p) \ +({ \ + typeof(p) _________p1 = ACCESS_ONCE(p); \ + smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ + (_________p1); \ +}) + +/** * rcu_assign_pointer() - assign to RCU-protected pointer * @p: pointer to assign to * @v: value to assign (publish)