From mboxrd@z Thu Jan 1 00:00:00 1970 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) From: Paolo Bonzini Date: Mon, 27 Feb 2017 12:17:26 +0100 Message-Id: <20170227111726.9237-1-pbonzini@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: [Qemu-devel] [PATCH] tests-aio-multithread: use atomic_read properly List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: stefanha@redhat.com 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 --- 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