From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52967) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bm0sR-0005AE-2w for qemu-devel@nongnu.org; Mon, 19 Sep 2016 11:53:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bm0sN-0005A7-LA for qemu-devel@nongnu.org; Mon, 19 Sep 2016 11:53:03 -0400 Received: from mail-lf0-f41.google.com ([209.85.215.41]:33751) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bm0sN-00059k-Dh for qemu-devel@nongnu.org; Mon, 19 Sep 2016 11:52:59 -0400 Received: by mail-lf0-f41.google.com with SMTP id h127so117158447lfh.0 for ; Mon, 19 Sep 2016 08:52:59 -0700 (PDT) From: =?UTF-8?q?Alex=20Benn=C3=A9e?= Date: Mon, 19 Sep 2016 16:51:36 +0100 Message-Id: <20160919155139.28371-6-alex.bennee@linaro.org> In-Reply-To: <20160919155139.28371-1-alex.bennee@linaro.org> References: <20160919155139.28371-1-alex.bennee@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: [Qemu-devel] [RFC 5/8] qom/object: update class cache atomically List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org, pbonzini@redhat.com, cota@braap.org, stefanha@redhat.com, kwolf@redhat.com Cc: mttcg@listserver.greensocs.com, fred.konrad@greensocs.com, a.rigo@virtualopensystems.com, bobby.prani@gmail.com, nikunj@linux.vnet.ibm.com, mark.burton@greensocs.com, jan.kiszka@siemens.com, serge.fdrv@gmail.com, rth@twiddle.net, peter.maydell@linaro.org, claudio.fontana@huawei.com, =?UTF-8?q?Alex=20Benn=C3=A9e?= , =?UTF-8?q?Andreas=20F=C3=A4rber?= The idiom CPU_GET_CLASS(cpu) is fairly extensively used in various threads and trips of ThreadSanitizer due to the fact it updates obj->class->object_cast_cache behind the scenes. As this is just a fast-path cache there is no need to lock updates just ensure that we don't get torn-updates from two racing lookups. While this is unlikely on x86 we use the plain atomic_read/set primitives to make this explicit and keep the sanitizer happy. Signed-off-by: Alex Bennée --- qom/object.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/qom/object.c b/qom/object.c index 8166b7d..7a05e35 100644 --- a/qom/object.c +++ b/qom/object.c @@ -614,7 +614,7 @@ Object *object_dynamic_cast_assert(Object *obj, const char *typename, Object *inst; for (i = 0; obj && i < OBJECT_CLASS_CAST_CACHE; i++) { - if (obj->class->object_cast_cache[i] == typename) { + if (atomic_read(&obj->class->object_cast_cache[i]) == typename) { goto out; } } @@ -631,10 +631,10 @@ Object *object_dynamic_cast_assert(Object *obj, const char *typename, if (obj && obj == inst) { for (i = 1; i < OBJECT_CLASS_CAST_CACHE; i++) { - obj->class->object_cast_cache[i - 1] = - obj->class->object_cast_cache[i]; + atomic_set(&obj->class->object_cast_cache[i - 1], + atomic_read(&obj->class->object_cast_cache[i])); } - obj->class->object_cast_cache[i - 1] = typename; + atomic_set(&obj->class->object_cast_cache[i - 1], typename); } out: @@ -704,7 +704,7 @@ ObjectClass *object_class_dynamic_cast_assert(ObjectClass *class, int i; for (i = 0; class && i < OBJECT_CLASS_CAST_CACHE; i++) { - if (class->class_cast_cache[i] == typename) { + if (atomic_read(&class->class_cast_cache[i]) == typename) { ret = class; goto out; } @@ -725,9 +725,10 @@ ObjectClass *object_class_dynamic_cast_assert(ObjectClass *class, #ifdef CONFIG_QOM_CAST_DEBUG if (class && ret == class) { for (i = 1; i < OBJECT_CLASS_CAST_CACHE; i++) { - class->class_cast_cache[i - 1] = class->class_cast_cache[i]; + atomic_set(&class->class_cast_cache[i - 1], + atomic_read(&class->class_cast_cache[i])); } - class->class_cast_cache[i - 1] = typename; + atomic_set(&class->class_cast_cache[i - 1], typename); } out: #endif -- 2.9.3