From 12d7e946a18c1040df21c95ceaaca88923206690 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Alex=20Benn=C3=A9e?= Date: Mon, 26 Feb 2018 05:06:37 -0500 Subject: [PATCH] qom/object: update class cache atomically 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. However to ensure defined C11 behaviour across threads we need to use the plain atomic_read/set primitives and keep the sanitizer happy. Backports commit b6b3ccfda015dcd5ab50f70c189ee5cc6c622e91 from qemu --- qemu/qom/object.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/qemu/qom/object.c b/qemu/qom/object.c index eb2e5dc5..4a3152cc 100644 --- a/qemu/qom/object.c +++ b/qemu/qom/object.c @@ -498,7 +498,7 @@ Object *object_dynamic_cast_assert(struct uc_struct *uc, Object *obj, const char 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; } } @@ -515,10 +515,10 @@ Object *object_dynamic_cast_assert(struct uc_struct *uc, Object *obj, const char 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: @@ -585,7 +585,7 @@ ObjectClass *object_class_dynamic_cast_assert(struct uc_struct *uc, ObjectClass 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; } @@ -606,9 +606,10 @@ ObjectClass *object_class_dynamic_cast_assert(struct uc_struct *uc, ObjectClass #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