From patchwork Tue Sep 6 18:00:26 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 3895 Return-Path: X-Original-To: patchwork@peony.canonical.com Delivered-To: patchwork@peony.canonical.com Received: from fiordland.canonical.com (fiordland.canonical.com [91.189.94.145]) by peony.canonical.com (Postfix) with ESMTP id F221723F9F for ; Wed, 7 Sep 2011 06:20:36 +0000 (UTC) Received: from mail-fx0-f52.google.com (mail-fx0-f52.google.com [209.85.161.52]) by fiordland.canonical.com (Postfix) with ESMTP id E2211A181E3 for ; Wed, 7 Sep 2011 06:20:36 +0000 (UTC) Received: by mail-fx0-f52.google.com with SMTP id 18so398726fxd.11 for ; Tue, 06 Sep 2011 23:20:36 -0700 (PDT) Received: by 10.223.88.214 with SMTP id b22mr2929383fam.5.1315376436811; Tue, 06 Sep 2011 23:20:36 -0700 (PDT) X-Forwarded-To: linaro-patchwork@canonical.com X-Forwarded-For: patch@linaro.org linaro-patchwork@canonical.com Delivered-To: patches@linaro.org Received: by 10.152.11.8 with SMTP id m8cs127754lab; Tue, 6 Sep 2011 23:20:36 -0700 (PDT) Received: by 10.101.53.11 with SMTP id f11mr4331855ank.72.1315376434572; Tue, 06 Sep 2011 23:20:34 -0700 (PDT) Received: from e3.ny.us.ibm.com (e3.ny.us.ibm.com [32.97.182.143]) by mx.google.com with ESMTPS id w20si5495456anf.73.2011.09.06.23.20.33 (version=TLSv1/SSLv3 cipher=OTHER); Tue, 06 Sep 2011 23:20:33 -0700 (PDT) Received-SPF: pass (google.com: domain of paulmck@linux.vnet.ibm.com designates 32.97.182.143 as permitted sender) client-ip=32.97.182.143; Authentication-Results: mx.google.com; spf=pass (google.com: domain of paulmck@linux.vnet.ibm.com designates 32.97.182.143 as permitted sender) smtp.mail=paulmck@linux.vnet.ibm.com Received: from d01relay01.pok.ibm.com (d01relay01.pok.ibm.com [9.56.227.233]) by e3.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id p875tjOu022478 for ; Wed, 7 Sep 2011 01:55:45 -0400 Received: from d01av01.pok.ibm.com (d01av01.pok.ibm.com [9.56.224.215]) by d01relay01.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p876KWHM237200 for ; Wed, 7 Sep 2011 02:20:32 -0400 Received: from d01av01.pok.ibm.com (loopback [127.0.0.1]) by d01av01.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p876KUpY004335 for ; Wed, 7 Sep 2011 02:20:32 -0400 Received: from paulmck-ThinkPad-W500 (dyn9050016039.mts.ibm.com [9.50.16.39] (may be forged)) by d01av01.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id p876KR7P004233; Wed, 7 Sep 2011 02:20:29 -0400 Received: by paulmck-ThinkPad-W500 (Postfix, from userid 1000) id 8A7FF13F888; Tue, 6 Sep 2011 11:00:52 -0700 (PDT) From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, patches@linaro.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 32/55] rcu: Make rcu_assign_pointer() unconditionally insert a memory barrier Date: Tue, 6 Sep 2011 11:00:26 -0700 Message-Id: <1315332049-2604-32-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.3.2 In-Reply-To: <20110906180015.GA2560@linux.vnet.ibm.com> References: <20110906180015.GA2560@linux.vnet.ibm.com> From: Eric Dumazet Recent changes to gcc give warning messages on rcu_assign_pointers()'s checks that allow it to determine when it is OK to omit the memory barrier. Stephen Hemminger tried a number of gcc tricks to silence this warning, but #pragmas and CPP macros do not work together in the way that would be required to make this work. However, we now have RCU_INIT_POINTER(), which already omits this memory barrier, and which therefore may be used when assigning NULL to an RCU-protected pointer that is accessible to readers. This commit therefore makes rcu_assign_pointer() unconditionally emit the memory barrier. Reported-by: Stephen Hemminger Signed-off-by: Eric Dumazet Acked-by: David S. Miller Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 4 +--- 1 files changed, 1 insertions(+), 3 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index ea80396..b2e5fe8 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -443,9 +443,7 @@ extern int rcu_my_thread_group_empty(void); }) #define __rcu_assign_pointer(p, v, space) \ ({ \ - if (!__builtin_constant_p(v) || \ - ((v) != NULL)) \ - smp_wmb(); \ + smp_wmb(); \ (p) = (typeof(*v) __force space *)(v); \ })