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qom/object: update class cache atomically

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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.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20160930213106.20186-7-alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Alex Bennée 2016-09-30 22:30:57 +01:00 committed by Paolo Bonzini
parent f96a8cc3c6
commit b6b3ccfda0
1 changed files with 8 additions and 7 deletions
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15
qom/object.c
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@ -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