From patchwork Mon Oct 9 18:28:47 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Rutland X-Patchwork-Id: 115289 Delivered-To: patch@linaro.org Received: by 10.140.22.163 with SMTP id 32csp2863308qgn; Mon, 9 Oct 2017 11:31:51 -0700 (PDT) X-Google-Smtp-Source: AOwi7QCRvdePDRV3EuSXqLSKnkJwbs9RQSwIrRiD+icwhJn6ga7V7K56VlnQ+NARENvE+zMMjrUC X-Received: by 10.101.88.142 with SMTP id d14mr9696715pgu.36.1507573911178; Mon, 09 Oct 2017 11:31:51 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1507573911; cv=none; d=google.com; s=arc-20160816; b=swWm5ezcHqoMZL7cj1gNX7guTY0QxpohceXLvhU7p0cKRtvVUeT6w+iY8wPnQbVqDB Ht+p6X/06fmh8zZOLadyXiee3RQllnH9W0S67Kce+wSsr0UvfD15d/qA8mtuJDTBHLxQ QrAT3WzhpwiZtpz8MoJR58quuhrWKnhCjrQqYqsMsQSHiLzrZbt5GEVZIl1ytkUNYVCN u3LvvxwtbtnqIKhtq/M+zYqFS8Rx9sC+uKVT/5pR18w9eisJss5/MloRA18Fz4SFgdwo FodlDnP4QivQg5zFR3P3GlWqq7d5wIycnnMo0JXDRCBK7exIzXwWRSvz3bCH4rXZ1JAJ zQ/w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:references:in-reply-to:message-id:date :subject:cc:to:from:arc-authentication-results; bh=E/QFAxyDk0C/AxXreYU9Z1KKgYA+uJV2mfT6BN6hn6Q=; b=VM1jkfu0gNknJFm6BYgGB6oGcpBv5tFXRU+nfhK+rQ0Dgme/ED9V9vfKen3fPOPKVK szZuA9iT2KztxXt6xV9Z4id7DtYn9BMwbzYPMMP+iA9jwPVvjrJKTAbrRTPzgx2YltZ8 h/yhPGMQGQS6dxkyGUTZQggZkCjs93D4FcUCkcp0gVu2v8nspBCZ1mahecfSyzDeGza7 rUOA+rHE3XpnPFChqM2G+a88QrUFai6s1bUklZghy9yTBGpchIi2qFRTFL+vB8xnlQ7h X4rie8ADwGzaPr3uA5t/R/OGUVxmKyuC1ySPJFWVgXJdVKUgp4F6maO6cq+g5Esbgnzs jccg== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id o29si3658752pfi.90.2017.10.09.11.31.50; Mon, 09 Oct 2017 11:31:51 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755438AbdJISbs (ORCPT + 26 others); 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 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 49146165C; Mon, 9 Oct 2017 11:30:56 -0700 (PDT) Received: from leverpostej.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id A53923F483; Mon, 9 Oct 2017 11:30:55 -0700 (PDT) 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 Precedence: bulk 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(-) -- 1.9.1 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__,