From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755429AbdJISbO (ORCPT ); Mon, 9 Oct 2017 14:31:14 -0400 Received: from foss.arm.com ([217.140.101.70]:33848 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754216AbdJISbB (ORCPT ); Mon, 9 Oct 2017 14:31:01 -0400 From: Mark Rutland To: linux-kernel@vger.kernel.org Cc: Mark Rutland , "Paul E. McKenney" Subject: [PATCH 13/13] rcutorture: formal: prepare for ACCESS_ONCE() removal Date: Mon, 9 Oct 2017 19:28:50 +0100 Message-Id: <1507573730-8083-14-git-send-email-mark.rutland@arm.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1507573730-8083-1-git-send-email-mark.rutland@arm.com> References: <1507573730-8083-1-git-send-email-mark.rutland@arm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org For several reasons, it is desirable to use {READ,WRITE}_ONCE() in preference to ACCESS_ONCE(), and new code is expected to use one of the former. So far, there's been no reason to change most existing uses of ACCESS_ONCE(), as these aren't currently harmful. However, for some features it is necessary to instrument reads and writes separately, which is not possible with ACCESS_ONCE(). This distinction is critical to correct operation. The bulk of the kernel code can be transformed via Coccinelle to use {READ,WRITE}_ONCE(), though this only modifies users of ACCESS_ONCE(), and not the implementation itself. As such, it has the potential to break homebrew ACCESS_ONCE() macros seen in some user code in the kernel tree (e.g. the virtio code, as fixed in commit ea9156fb3b71d9f7). To avoid fragility if/when that transformation occurs, this patch reworks the rcutorture formal tests to use an intermediate __ACCESS_ONCE() helper, which will avoid {READ,WRITE}_ONCE() being turned into tautological definitions. There should be no functional change as a result of this patch. Cc: Paul E. McKenney Signed-off-by: Mark Rutland --- tools/testing/selftests/rcutorture/formal/srcu-cbmc/src/barriers.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/tools/testing/selftests/rcutorture/formal/srcu-cbmc/src/barriers.h b/tools/testing/selftests/rcutorture/formal/srcu-cbmc/src/barriers.h index 6687acc..ee4e4f8 100644 --- a/tools/testing/selftests/rcutorture/formal/srcu-cbmc/src/barriers.h +++ b/tools/testing/selftests/rcutorture/formal/srcu-cbmc/src/barriers.h @@ -34,8 +34,9 @@ #define rs_smp_mb() do {} while (0) #endif -#define ACCESS_ONCE(x) (*(volatile typeof(x) *) &(x)) -#define READ_ONCE(x) ACCESS_ONCE(x) -#define WRITE_ONCE(x, val) (ACCESS_ONCE(x) = (val)) +#define __ACCESS_ONCE(x) (*(volatile typeof(x) *) &(x)) +#define ACCESS_ONCE(x) __ACCESS_ONCE(x) +#define READ_ONCE(x) __ACCESS_ONCE(x) +#define WRITE_ONCE(x, val) (__ACCESS_ONCE(x) = (val)) #endif -- 1.9.1