From nobody Sun Apr 13 18:17:55 2025 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 14882141743881023.7287738360837; Mon, 27 Feb 2017 08:49:34 -0800 (PST) Received: from localhost ([::1]:54256 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ciOUO-0003M0-Lp for importer@patchew.org; Mon, 27 Feb 2017 11:49:32 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45921) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ciOGK-0007rg-7f for qemu-devel@nongnu.org; Mon, 27 Feb 2017 11:35:01 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ciOGH-0008Q8-PN for qemu-devel@nongnu.org; Mon, 27 Feb 2017 11:35:00 -0500 Received: from mx1.redhat.com ([209.132.183.28]:58056) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ciOGH-0008Q1-Jk for qemu-devel@nongnu.org; Mon, 27 Feb 2017 11:34:57 -0500 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) (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 C175A7E9D8; Mon, 27 Feb 2017 16:34:57 +0000 (UTC) Received: from localhost (ovpn-117-188.ams2.redhat.com [10.36.117.188]) by int-mx11.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id v1RGYu1x020020; Mon, 27 Feb 2017 11:34:57 -0500 From: Stefan Hajnoczi To: Date: Mon, 27 Feb 2017 16:34:47 +0000 Message-Id: <20170227163447.20428-5-stefanha@redhat.com> In-Reply-To: <20170227163447.20428-1-stefanha@redhat.com> References: <20170227163447.20428-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.68 on 10.5.11.24 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Mon, 27 Feb 2017 16:34:57 +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] [PULL 4/4] 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: Peter Maydell , Stefan Hajnoczi , Paolo Bonzini 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" From: Paolo Bonzini 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 Message-id: 20170227111726.9237-1-pbonzini@redhat.com Signed-off-by: Stefan Hajnoczi --- 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