From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: [PATCH 11/19] selftests/powerpc: Kill off ACCESS_ONCE() Date: Mon, 23 Oct 2017 14:07:21 -0700 Message-ID: <1508792849-3115-11-git-send-email-paulmck@linux.vnet.ibm.com> References: <20171023210408.GA2930@linux.vnet.ibm.com> Return-path: In-Reply-To: <20171023210408.GA2930@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org To: mingo@kernel.org Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, will.deacon@arm.com, mark.rutland@arm.com, snitzer@redhat.com, thor.thayer@linux.intel.com, viro@zeniv.linux.org.uk, davem@davemloft.net, shuah@kernel.org, mpe@ellerman.id.au, tj@kernel.org, torvalds@linux-foundation.org, Benjamin Herrenschmidt , Paul Mackerras List-Id: linux-arch.vger.kernel.org From: Mark Rutland 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, and to align with the preferred usage of {READ,WRITE}_ONCE(), this patch updates the DSCR selftest code to use READ_ONCE() rather than ACCESS_ONCE(). There should be no functional change as a result of this patch. Signed-off-by: Mark Rutland Acked-by: Michael Ellerman Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Shuah Khan --- tools/testing/selftests/powerpc/dscr/dscr.h | 2 +- tools/testing/selftests/powerpc/dscr/dscr_default_test.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/powerpc/dscr/dscr.h b/tools/testing/selftests/powerpc/dscr/dscr.h index 18ea223bd398..cdb840bc54f2 100644 --- a/tools/testing/selftests/powerpc/dscr/dscr.h +++ b/tools/testing/selftests/powerpc/dscr/dscr.h @@ -39,7 +39,7 @@ #define rmb() asm volatile("lwsync":::"memory") #define wmb() asm volatile("lwsync":::"memory") -#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) +#define READ_ONCE(x) (*(volatile typeof(x) *)&(x)) /* Prilvilege state DSCR access */ inline unsigned long get_dscr(void) diff --git a/tools/testing/selftests/powerpc/dscr/dscr_default_test.c b/tools/testing/selftests/powerpc/dscr/dscr_default_test.c index df17c3bab0a7..9e1a37e93b63 100644 --- a/tools/testing/selftests/powerpc/dscr/dscr_default_test.c +++ b/tools/testing/selftests/powerpc/dscr/dscr_default_test.c @@ -27,7 +27,7 @@ static void *do_test(void *in) unsigned long d, cur_dscr, cur_dscr_usr; unsigned long s1, s2; - s1 = ACCESS_ONCE(sequence); + s1 = READ_ONCE(sequence); if (s1 & 1) continue; rmb(); -- 2.5.2 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:40048 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751576AbdJWVHl (ORCPT ); Mon, 23 Oct 2017 17:07:41 -0400 Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v9NL7Oqd124686 for ; Mon, 23 Oct 2017 17:07:41 -0400 Received: from e11.ny.us.ibm.com (e11.ny.us.ibm.com [129.33.205.201]) by mx0a-001b2d01.pphosted.com with ESMTP id 2dskcm4tsx-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 23 Oct 2017 17:07:41 -0400 Received: from localhost by e11.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 23 Oct 2017 17:07:39 -0400 From: "Paul E. McKenney" Subject: [PATCH 11/19] selftests/powerpc: Kill off ACCESS_ONCE() Date: Mon, 23 Oct 2017 14:07:21 -0700 In-Reply-To: <20171023210408.GA2930@linux.vnet.ibm.com> References: <20171023210408.GA2930@linux.vnet.ibm.com> Message-ID: <1508792849-3115-11-git-send-email-paulmck@linux.vnet.ibm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: mingo@kernel.org Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, will.deacon@arm.com, mark.rutland@arm.com, snitzer@redhat.com, thor.thayer@linux.intel.com, viro@zeniv.linux.org.uk, davem@davemloft.net, shuah@kernel.org, mpe@ellerman.id.au, tj@kernel.org, torvalds@linux-foundation.org, Benjamin Herrenschmidt , Paul Mackerras Message-ID: <20171023210721.pIZLZODpsVZbaTSBxH1piqvKlIH6r-v3RoMppYVWcdg@z> From: Mark Rutland 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, and to align with the preferred usage of {READ,WRITE}_ONCE(), this patch updates the DSCR selftest code to use READ_ONCE() rather than ACCESS_ONCE(). There should be no functional change as a result of this patch. Signed-off-by: Mark Rutland Acked-by: Michael Ellerman Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Shuah Khan --- tools/testing/selftests/powerpc/dscr/dscr.h | 2 +- tools/testing/selftests/powerpc/dscr/dscr_default_test.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/powerpc/dscr/dscr.h b/tools/testing/selftests/powerpc/dscr/dscr.h index 18ea223bd398..cdb840bc54f2 100644 --- a/tools/testing/selftests/powerpc/dscr/dscr.h +++ b/tools/testing/selftests/powerpc/dscr/dscr.h @@ -39,7 +39,7 @@ #define rmb() asm volatile("lwsync":::"memory") #define wmb() asm volatile("lwsync":::"memory") -#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) +#define READ_ONCE(x) (*(volatile typeof(x) *)&(x)) /* Prilvilege state DSCR access */ inline unsigned long get_dscr(void) diff --git a/tools/testing/selftests/powerpc/dscr/dscr_default_test.c b/tools/testing/selftests/powerpc/dscr/dscr_default_test.c index df17c3bab0a7..9e1a37e93b63 100644 --- a/tools/testing/selftests/powerpc/dscr/dscr_default_test.c +++ b/tools/testing/selftests/powerpc/dscr/dscr_default_test.c @@ -27,7 +27,7 @@ static void *do_test(void *in) unsigned long d, cur_dscr, cur_dscr_usr; unsigned long s1, s2; - s1 = ACCESS_ONCE(sequence); + s1 = READ_ONCE(sequence); if (s1 & 1) continue; rmb(); -- 2.5.2