QObject: fix memory order on load/store of signal spy callback set

QSignalSpyCallbackSet is a set of pointers, so when we store a pointer
to it for later dereferencing, we need to use a release fence for the
store and a corresponding acquire on load, lest the two don't
synchronize with each other and we end up with a data race.

Amends a65752c71bd25bbb66bf33d3a82f7901419c5d95.

Change-Id: Ic2983d76237c5c5b00eb2a3575b10beb84d57190
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

1 files changed, 2 insertions, 2 deletions

diff --git a/src/corelib/kernel/qobject.cpp b/src/corelib/kernel/qobject.cpp
index 7eba9b05ff..8f80be30bd 100644
--- a/src/corelib/kernel/qobject.cpp
+++ b/src/corelib/kernel/qobject.cpp
@@ -82,7 +82,7 @@ Q_CORE_EXPORT QBasicAtomicPointer<QSignalSpyCallbackSet> qt_signal_spy_callback_
 
 void qt_register_signal_spy_callbacks(QSignalSpyCallbackSet *callback_set)
 {
-    qt_signal_spy_callback_set.store(callback_set);
+    qt_signal_spy_callback_set.storeRelease(callback_set);
 }
 
 QDynamicMetaObjectData::~QDynamicMetaObjectData()
@@ -3696,7 +3696,7 @@ void doActivate(QObject *sender, int signal_index, void **argv)
                                                 signal_index, argv);
     }
 
-    const QSignalSpyCallbackSet *signal_spy_set = callbacks_enabled ? qt_signal_spy_callback_set.load() : nullptr;
+    const QSignalSpyCallbackSet *signal_spy_set = callbacks_enabled ? qt_signal_spy_callback_set.loadAcquire() : nullptr;
 
     void *empty_argv[] = { nullptr };
     if (!argv)