From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932709AbdJYKYz (ORCPT ); Wed, 25 Oct 2017 06:24:55 -0400 Received: from terminus.zytor.com ([65.50.211.136]:57739 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932495AbdJYKYu (ORCPT ); Wed, 25 Oct 2017 06:24:50 -0400 Date: Wed, 25 Oct 2017 03:20:16 -0700 From: tip-bot for Mark Rutland Message-ID: Cc: torvalds@linux-foundation.org, peterz@infradead.org, mingo@kernel.org, tj@kernel.org, jiangshanlai@gmail.com, hpa@zytor.com, linux-kernel@vger.kernel.org, paulmck@linux.vnet.ibm.com, tglx@linutronix.de, mark.rutland@arm.com Reply-To: linux-kernel@vger.kernel.org, mark.rutland@arm.com, tglx@linutronix.de, paulmck@linux.vnet.ibm.com, tj@kernel.org, mingo@kernel.org, peterz@infradead.org, torvalds@linux-foundation.org, hpa@zytor.com, jiangshanlai@gmail.com In-Reply-To: <1508792849-3115-12-git-send-email-paulmck@linux.vnet.ibm.com> References: <1508792849-3115-12-git-send-email-paulmck@linux.vnet.ibm.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:locking/core] locking/atomics, workqueue: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE() Git-Commit-ID: c95491ed6d6a958743d82bea1d053819988da418 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: c95491ed6d6a958743d82bea1d053819988da418 Gitweb: https://git.kernel.org/tip/c95491ed6d6a958743d82bea1d053819988da418 Author: Mark Rutland AuthorDate: Mon, 23 Oct 2017 14:07:22 -0700 Committer: Ingo Molnar CommitDate: Wed, 25 Oct 2017 11:01:03 +0200 locking/atomics, workqueue: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE() 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 Signed-off-by: Paul E. McKenney Acked-by: Tejun Heo Cc: Lai Jiangshan Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: davem@davemloft.net Cc: linux-arch@vger.kernel.org Cc: mpe@ellerman.id.au Cc: shuah@kernel.org Cc: snitzer@redhat.com Cc: thor.thayer@linux.intel.com Cc: viro@zeniv.linux.org.uk Cc: will.deacon@arm.com Link: http://lkml.kernel.org/r/1508792849-3115-12-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar --- kernel/workqueue.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) 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);