Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933248AbbHXJPn (ORCPT ); Mon, 24 Aug 2015 05:15:43 -0400 Received: from mx2.suse.de ([195.135.220.15]:58181 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932827AbbHXJKP (ORCPT ); Mon, 24 Aug 2015 05:10:15 -0400 X-Amavis-Alert: BAD HEADER SECTION, Duplicate header field: "References" From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, "Paul E. McKenney" , Al Viro , Jiri Slaby Subject: [PATCH 3.12 61/82] rcu: Provide counterpart to rcu_dereference() for non-RCU situations Date: Mon, 24 Aug 2015 11:09:21 +0200 Message-Id: X-Mailer: git-send-email 2.5.0 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1969 Lines: 55 From: "Paul E. McKenney" 3.12-stable review patch. If anyone has any objections, please let me know. =============== 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 Signed-off-by: Jiri Slaby --- include/linux/rcupdate.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index f1f1bc39346b..4912c953cab7 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -554,6 +554,20 @@ static inline void rcu_preempt_sleep_check(void) (p) = (typeof(*v) __force space *)(v); \ } while (0) +/** + * 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_access_pointer() - fetch RCU pointer with no dereferencing -- 2.5.0 -- 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/