From patchwork Mon Oct 9 18:28:49 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Rutland X-Patchwork-Id: 115286 Delivered-To: patch@linaro.org Received: by 10.140.22.163 with SMTP id 32csp2862611qgn; Mon, 9 Oct 2017 11:31:04 -0700 (PDT) X-Google-Smtp-Source: AOwi7QBeIfRN4hS/iPiD8lNo20laXdT74XpW+NDTMyfzgVAjtTUiZdl0FezFjk8IcAcWwN6YTgpE X-Received: by 10.99.107.73 with SMTP id g70mr9705426pgc.279.1507573864795; Mon, 09 Oct 2017 11:31:04 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1507573864; cv=none; d=google.com; s=arc-20160816; b=I8Ynu0yPtahEGChw9OBKijBwVnMlkJFekqjNRpn0aPlPGsV3AYP9KH3H9JORS70VpF ZtGenvvtv2oBMdA+oSNRuNRevwkoMCZDdrg5RZLpJcGDeeXcdQDstMf0Ro4vYdQapIcP /EJ3o/Ff/cmQbKlnAe70MD2gsEJdHSr9YBWbsgZ2ZQmC4btlql5AjMG5/TBqE+v/By0+ bMTi05WgOdoufN4mHeckwG0+8WYujGEjjEf2N9T4njltIozms7KgIhSnZxqiZhmI4LRi YRpAgT8d6LNxvQX7Nxxt0d7mdKYKUEe9YoParJxMpDOsxuKsd8EHdoO+1wWPK4dLq+AG 2Ayw== 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=/YRTTht65u4X6k6ScfrE4pfLraxmdN18u1G14kcQvj8=; b=q/36qA+aGhgiXIFg75geNc/n63KXTlLe7hMuN+nM4w6RFpJeA+okI+4RgUgLgao1GL dQ4Ol7o+fksjuu0zpjL4XOtp5gHiwgjVEDRopu+JUW+OzUfMQTKNnXX0x2zvyz89VmK2 sVHERNXeHa9NzlCsKEvvb3QL3kt7+CLwhziHB4rY/MXVSjgv/KW01DGOD0xxEXS4I3Xh FEPdnhJvYqqCvLp+GmOHfpnXVGYROIv/h5JADP4PUSJN+8xdnXIdRGyiE6PfTSGsE2LA NZwn9kmhw+puSnJc7cyQS5ye+Bi8EY2C8BAGycY44jYoZGZ6AXpp2Z27x/K2+4NXGHT6 LG6A== 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 e72si7432058pfm.35.2017.10.09.11.31.04; Mon, 09 Oct 2017 11:31:04 -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 S1755418AbdJISbC (ORCPT + 26 others); Mon, 9 Oct 2017 14:31:02 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:33840 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755176AbdJISbA (ORCPT ); Mon, 9 Oct 2017 14:31:00 -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 B9296165D; Mon, 9 Oct 2017 11:30:59 -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 CE44B3F483; Mon, 9 Oct 2017 11:30:58 -0700 (PDT) From: Mark Rutland To: linux-kernel@vger.kernel.org Cc: Mark Rutland , Lai Jiangshan , Tejun Heo Subject: [PATCH 12/13] workqueue: kill off ACCESS_ONCE() Date: Mon, 9 Oct 2017 19:28:49 +0100 Message-Id: <1507573730-8083-13-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. It's possible to transform the bulk of kernel code using the Coccinelle script below. However, this doesn't handle comments, leaving references to ACCESS_ONCE() instances which have been removed. As a preparatory step, this patch converts the workqueue code and comments to use {READ,WRITE}_ONCE() consistently. ---- virtual patch @ depends on patch @ expression E1, E2; @@ - ACCESS_ONCE(E1) = E2 + WRITE_ONCE(E1, E2) @ depends on patch @ expression E; @@ - ACCESS_ONCE(E) + READ_ONCE(E) ---- Signed-off-by: Mark Rutland Cc: Lai Jiangshan Cc: Tejun Heo --- kernel/workqueue.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) -- 1.9.1 Acked-by: Tejun Heo diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 64d0edf..39831b2 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -4647,7 +4647,7 @@ static void rebind_workers(struct worker_pool *pool) * concurrency management. Note that when or whether * @worker clears REBOUND doesn't affect correctness. * - * ACCESS_ONCE() is necessary because @worker->flags may be + * WRITE_ONCE() is necessary because @worker->flags may be * tested without holding any lock in * wq_worker_waking_up(). Without it, NOT_RUNNING test may * fail incorrectly leading to premature concurrency @@ -4656,7 +4656,7 @@ static void rebind_workers(struct worker_pool *pool) WARN_ON_ONCE(!(worker_flags & WORKER_UNBOUND)); worker_flags |= WORKER_REBOUND; worker_flags &= ~WORKER_UNBOUND; - ACCESS_ONCE(worker->flags) = worker_flags; + WRITE_ONCE(worker->flags, worker_flags); } spin_unlock_irq(&pool->lock);