From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755437AbdJISbs (ORCPT ); Mon, 9 Oct 2017 14:31:48 -0400 Received: from foss.arm.com ([217.140.101.70]:33820 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755341AbdJISa4 (ORCPT ); Mon, 9 Oct 2017 14:30:56 -0400 From: Mark Rutland To: linux-kernel@vger.kernel.org Cc: Mark Rutland , Shuah Khan Subject: [PATCH 10/13] samples: mic/mpssd/mpssd.c: kill off ACCESS_ONCE() Date: Mon, 9 Oct 2017 19:28:47 +0100 Message-Id: <1507573730-8083-11-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, and to align with the preferred usage of {READ,WRITE}_ONCE(), this patch updates the MPSSD sample 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 Cc: Shuah Khan --- samples/mic/mpssd/mpssd.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/samples/mic/mpssd/mpssd.c b/samples/mic/mpssd/mpssd.c index 49db1de..f42ce55 100644 --- a/samples/mic/mpssd/mpssd.c +++ b/samples/mic/mpssd/mpssd.c @@ -65,7 +65,7 @@ /* to align the pointer to the (next) page boundary */ #define PAGE_ALIGN(addr) _ALIGN(addr, PAGE_SIZE) -#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) +#define READ_ONCE(x) (*(volatile typeof(x) *)&(x)) #define GSO_ENABLED 1 #define MAX_GSO_SIZE (64 * 1024) @@ -382,7 +382,7 @@ static inline void verify_out_len(struct mic_info *mic, static inline __u16 read_avail_idx(struct mic_vring *vr) { - return ACCESS_ONCE(vr->info->avail_idx); + return READ_ONCE(vr->info->avail_idx); } static inline void txrx_prepare(int type, bool tx, struct mic_vring *vr, @@ -523,7 +523,7 @@ static inline unsigned _vring_size(unsigned int num, unsigned long align) { __u16 avail_idx = read_avail_idx(vr); - while (avail_idx == le16toh(ACCESS_ONCE(vr->vr.avail->idx))) { + while (avail_idx == le16toh(READ_ONCE(vr->vr.avail->idx))) { #ifdef DEBUG mpsslog("%s %s waiting for desc avail %d info_avail %d\n", mic->name, __func__, -- 1.9.1