From nobody Thu May 2 04:30:54 2024 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zoho.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1488194311425243.7644151108343; Mon, 27 Feb 2017 03:18:31 -0800 (PST) Received: from localhost ([::1]:51731 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ciJJz-0004xz-MF for importer@patchew.org; Mon, 27 Feb 2017 06:18:27 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43754) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ciJJ7-0004fm-Er for qemu-devel@nongnu.org; Mon, 27 Feb 2017 06:17:34 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ciJJ2-0000Eb-MF for qemu-devel@nongnu.org; Mon, 27 Feb 2017 06:17:33 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46872) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ciJJ2-0000EN-G1 for qemu-devel@nongnu.org; Mon, 27 Feb 2017 06:17:28 -0500 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 55C633A76A4 for ; Mon, 27 Feb 2017 11:17:28 +0000 (UTC) Received: from donizetti.redhat.com (ovpn-117-118.ams2.redhat.com [10.36.117.118]) by int-mx14.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id v1RBHQDr017274; Mon, 27 Feb 2017 06:17:27 -0500 From: Paolo Bonzini To: qemu-devel@nongnu.org Date: Mon, 27 Feb 2017 12:17:26 +0100 Message-Id: <20170227111726.9237-1-pbonzini@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.68 on 10.5.11.27 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Mon, 27 Feb 2017 11:17:28 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH] tests-aio-multithread: use atomic_read properly X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: stefanha@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Type: text/plain; charset="utf-8" nodes[id].next is written by other threads. If atomic_read is not used (matching atomic_set in mcs_mutex_lock!) the compiler can optimize the whole "if" away! Reported-by: Alex Benn=C3=A9e Signed-off-by: Paolo Bonzini Tested-by: Greg Kurz --- tests/test-aio-multithread.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/tests/test-aio-multithread.c b/tests/test-aio-multithread.c index f11e990..8b0b40e 100644 --- a/tests/test-aio-multithread.c +++ b/tests/test-aio-multithread.c @@ -309,7 +309,7 @@ static void mcs_mutex_lock(void) static void mcs_mutex_unlock(void) { int next; - if (nodes[id].next =3D=3D -1) { + if (atomic_read(&nodes[id].next) =3D=3D -1) { if (atomic_read(&mutex_head) =3D=3D id && atomic_cmpxchg(&mutex_head, id, -1) =3D=3D id) { /* Last item in the list, exit. */ @@ -323,7 +323,7 @@ static void mcs_mutex_unlock(void) } =20 /* Wake up the next in line. */ - next =3D nodes[id].next; + next =3D atomic_read(&nodes[id].next); nodes[next].locked =3D 0; qemu_futex_wake(&nodes[next].locked, 1); } --=20 2.9.3