Fix two data races in QThread/QThreadData

* theMainThread is written by the main thread and read by
   QThreadData::~QThreadData() (any managed thread)

* QThreadData::thread is written by QThread::~QThread (in the parent thread)
  and read+written by QThreadData::~QThreadData (in the managed thread).
  This can happen because QThreadData is refcounted so the managed
  thread (which derefs it) races with the parent thread (which sets it to 0).

Change-Id: I72de793716391a0937254cda6b4328fcad5060c7
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

4 files changed, 6 insertions, 6 deletions

diff --git a/src/corelib/thread/qthread_p.h b/src/corelib/thread/qthread_p.h
index 1ecd682ad1..8331816729 100644
--- a/src/corelib/thread/qthread_p.h
+++ b/src/corelib/thread/qthread_p.h
@@ -269,7 +269,7 @@ public:
 
     QStack<QEventLoop *> eventLoops;
     QPostEventList postEventList;
-    QThread *thread;
+    QAtomicPointer<QThread> thread;
     Qt::HANDLE threadId;
     QAtomicPointer<QAbstractEventDispatcher> eventDispatcher;
     QVector<void *> tls;
diff --git a/src/corelib/thread/qthread_unix.cpp b/src/corelib/thread/qthread_unix.cpp
index 77093c9cf1..5698a61326 100644
--- a/src/corelib/thread/qthread_unix.cpp
+++ b/src/corelib/thread/qthread_unix.cpp
@@ -225,7 +225,7 @@ QThreadData *QThreadData::current(bool createIfNecessary)
         data->isAdopted = true;
         data->threadId = (Qt::HANDLE)pthread_self();
         if (!QCoreApplicationPrivate::theMainThread)
-            QCoreApplicationPrivate::theMainThread = data->thread;
+            QCoreApplicationPrivate::theMainThread = data->thread.load();
     }
     return data;
 }
diff --git a/src/corelib/thread/qthread_win.cpp b/src/corelib/thread/qthread_win.cpp
index c16a2e958c..a4b853d62e 100644
--- a/src/corelib/thread/qthread_win.cpp
+++ b/src/corelib/thread/qthread_win.cpp
@@ -121,7 +121,7 @@ QThreadData *QThreadData::current(bool createIfNecessary)
         threadData->threadId = reinterpret_cast<Qt::HANDLE>(GetCurrentThreadId());
 
         if (!QCoreApplicationPrivate::theMainThread) {
-            QCoreApplicationPrivate::theMainThread = threadData->thread;
+            QCoreApplicationPrivate::theMainThread = threadData->thread.load();
             // TODO: is there a way to reflect the branch's behavior using
             // WinRT API?
         } else {
diff --git a/src/corelib/thread/qthreadstorage.cpp b/src/corelib/thread/qthreadstorage.cpp
index 05ab01cc54..37892233f3 100644
--- a/src/corelib/thread/qthreadstorage.cpp
+++ b/src/corelib/thread/qthreadstorage.cpp
@@ -121,7 +121,7 @@ void **QThreadStorageData::get() const
     DEBUG_MSG("QThreadStorageData: Returning storage %d, data %p, for thread %p",
           id,
           *v,
-          data->thread);
+          data->thread.load());
 
     return *v ? v : 0;
 }
@@ -143,7 +143,7 @@ void **QThreadStorageData::set(void *p)
         DEBUG_MSG("QThreadStorageData: Deleting previous storage %d, data %p, for thread %p",
                 id,
                 value,
-                data->thread);
+                data->thread.load());
 
         QMutexLocker locker(&destructorsMutex);
         DestructorMap *destr = destructors();
@@ -159,7 +159,7 @@ void **QThreadStorageData::set(void *p)
 
     // store new data
     value = p;
-    DEBUG_MSG("QThreadStorageData: Set storage %d for thread %p to %p", id, data->thread, p);
+    DEBUG_MSG("QThreadStorageData: Set storage %d for thread %p to %p", id, data->thread.load(), p);
     return &value;
 }